oxigraph/lib/oxrdf/src/triple.rs

use crate::blank_node::BlankNode;
use crate::cast_error::TripleConstructionError;
use crate::literal::Literal;
use crate::named_node::NamedNode;
use crate::{BlankNodeRef, LiteralRef, NamedNodeRef, TryFromTermError};
use std::fmt;

/// The owned union of [IRIs](https://www.w3.org/TR/rdf11-concepts/#dfn-iri) and [blank nodes](https://www.w3.org/TR/rdf11-concepts/#dfn-blank-node).
#[derive(Eq, PartialEq, Debug, Clone, Hash)]
pub enum NamedOrBlankNode {
    NamedNode(NamedNode),
    BlankNode(BlankNode),
}

impl NamedOrBlankNode {
    #[inline]
    pub fn is_named_node(&self) -> bool {
        self.as_ref().is_named_node()
    }

    #[inline]
    pub fn is_blank_node(&self) -> bool {
        self.as_ref().is_blank_node()
    }

    #[inline]
    pub fn as_ref(&self) -> NamedOrBlankNodeRef<'_> {
        match self {
            Self::NamedNode(node) => NamedOrBlankNodeRef::NamedNode(node.as_ref()),
            Self::BlankNode(node) => NamedOrBlankNodeRef::BlankNode(node.as_ref()),
        }
    }
}

impl fmt::Display for NamedOrBlankNode {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.as_ref().fmt(f)
    }
}

impl From<NamedNode> for NamedOrBlankNode {
    #[inline]
    fn from(node: NamedNode) -> Self {
        Self::NamedNode(node)
    }
}

impl From<NamedNodeRef<'_>> for NamedOrBlankNode {
    #[inline]
    fn from(node: NamedNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

impl From<BlankNode> for NamedOrBlankNode {
    #[inline]
    fn from(node: BlankNode) -> Self {
        Self::BlankNode(node)
    }
}

impl From<BlankNodeRef<'_>> for NamedOrBlankNode {
    #[inline]
    fn from(node: BlankNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

/// The borrowed union of [IRIs](https://www.w3.org/TR/rdf11-concepts/#dfn-iri) and [blank nodes](https://www.w3.org/TR/rdf11-concepts/#dfn-blank-node).
#[derive(Eq, PartialEq, Debug, Clone, Copy, Hash)]
pub enum NamedOrBlankNodeRef<'a> {
    NamedNode(NamedNodeRef<'a>),
    BlankNode(BlankNodeRef<'a>),
}

impl<'a> NamedOrBlankNodeRef<'a> {
    #[inline]
    pub fn is_named_node(&self) -> bool {
        match self {
            Self::NamedNode(_) => true,
            Self::BlankNode(_) => false,
        }
    }

    #[inline]
    pub fn is_blank_node(&self) -> bool {
        match self {
            Self::NamedNode(_) => false,
            Self::BlankNode(_) => true,
        }
    }

    #[inline]
    pub fn into_owned(self) -> NamedOrBlankNode {
        match self {
            Self::NamedNode(node) => NamedOrBlankNode::NamedNode(node.into_owned()),
            Self::BlankNode(node) => NamedOrBlankNode::BlankNode(node.into_owned()),
        }
    }
}

impl fmt::Display for NamedOrBlankNodeRef<'_> {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::NamedNode(node) => node.fmt(f),
            Self::BlankNode(node) => node.fmt(f),
        }
    }
}

impl<'a> From<NamedNodeRef<'a>> for NamedOrBlankNodeRef<'a> {
    #[inline]
    fn from(node: NamedNodeRef<'a>) -> Self {
        Self::NamedNode(node)
    }
}

impl<'a> From<&'a NamedNode> for NamedOrBlankNodeRef<'a> {
    #[inline]
    fn from(node: &'a NamedNode) -> Self {
        node.as_ref().into()
    }
}

impl<'a> From<BlankNodeRef<'a>> for NamedOrBlankNodeRef<'a> {
    #[inline]
    fn from(node: BlankNodeRef<'a>) -> Self {
        Self::BlankNode(node)
    }
}

impl<'a> From<&'a BlankNode> for NamedOrBlankNodeRef<'a> {
    #[inline]
    fn from(node: &'a BlankNode) -> Self {
        node.as_ref().into()
    }
}

impl<'a> From<&'a NamedOrBlankNode> for NamedOrBlankNodeRef<'a> {
    #[inline]
    fn from(node: &'a NamedOrBlankNode) -> Self {
        node.as_ref()
    }
}

impl<'a> From<NamedOrBlankNodeRef<'a>> for NamedOrBlankNode {
    #[inline]
    fn from(node: NamedOrBlankNodeRef<'a>) -> Self {
        node.into_owned()
    }
}

/// The owned union of [IRIs](https://www.w3.org/TR/rdf11-concepts/#dfn-iri), [blank nodes](https://www.w3.org/TR/rdf11-concepts/#dfn-blank-node)  and [triples](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple) (if the `rdf-star` feature is enabled).
#[derive(Eq, PartialEq, Debug, Clone, Hash)]
pub enum Subject {
    NamedNode(NamedNode),
    BlankNode(BlankNode),
    #[cfg(feature = "rdf-star")]
    Triple(Box<Triple>),
}

impl Subject {
    #[inline]
    pub fn is_named_node(&self) -> bool {
        self.as_ref().is_named_node()
    }

    #[inline]
    pub fn is_blank_node(&self) -> bool {
        self.as_ref().is_blank_node()
    }

    #[cfg(feature = "rdf-star")]
    #[inline]
    pub fn is_triple(&self) -> bool {
        self.as_ref().is_triple()
    }

    #[inline]
    pub fn as_ref(&self) -> SubjectRef<'_> {
        match self {
            Self::NamedNode(node) => SubjectRef::NamedNode(node.as_ref()),
            Self::BlankNode(node) => SubjectRef::BlankNode(node.as_ref()),
            #[cfg(feature = "rdf-star")]
            Self::Triple(triple) => SubjectRef::Triple(triple),
        }
    }
}

impl fmt::Display for Subject {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.as_ref().fmt(f)
    }
}

impl From<NamedNode> for Subject {
    #[inline]
    fn from(node: NamedNode) -> Self {
        Self::NamedNode(node)
    }
}

impl From<NamedNodeRef<'_>> for Subject {
    #[inline]
    fn from(node: NamedNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

impl From<BlankNode> for Subject {
    #[inline]
    fn from(node: BlankNode) -> Self {
        Self::BlankNode(node)
    }
}

impl From<BlankNodeRef<'_>> for Subject {
    #[inline]
    fn from(node: BlankNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

impl TryFrom<Term> for Subject {
    type Error = TryFromTermError;

    #[inline]
    fn try_from(term: Term) -> Result<Self, Self::Error> {
        match term {
            Term::NamedNode(node) => Ok(Subject::NamedNode(node)),
            Term::BlankNode(node) => Ok(Subject::BlankNode(node)),
            #[cfg(feature = "rdf-star")]
            Term::Triple(triple) => Ok(Subject::Triple(triple)),
            Term::Literal(_) => Err(TryFromTermError {
                term,
                target: "Subject",
            }),
        }
    }
}

#[cfg(feature = "rdf-star")]
impl From<Triple> for Subject {
    #[inline]
    fn from(node: Triple) -> Self {
        Self::Triple(Box::new(node))
    }
}

#[cfg(feature = "rdf-star")]
impl From<Box<Triple>> for Subject {
    #[inline]
    fn from(node: Box<Triple>) -> Self {
        Self::Triple(node)
    }
}

#[cfg(feature = "rdf-star")]
impl From<TripleRef<'_>> for Subject {
    #[inline]
    fn from(node: TripleRef<'_>) -> Self {
        node.into_owned().into()
    }
}

impl From<NamedOrBlankNode> for Subject {
    #[inline]
    fn from(node: NamedOrBlankNode) -> Self {
        match node {
            NamedOrBlankNode::NamedNode(node) => node.into(),
            NamedOrBlankNode::BlankNode(node) => node.into(),
        }
    }
}

impl From<NamedOrBlankNodeRef<'_>> for Subject {
    #[inline]
    fn from(node: NamedOrBlankNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

/// The borrowed union of [IRIs](https://www.w3.org/TR/rdf11-concepts/#dfn-iri), [blank nodes](https://www.w3.org/TR/rdf11-concepts/#dfn-blank-node) and [triples](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple) (if the `rdf-star` feature is enabled).
#[derive(Eq, PartialEq, Debug, Clone, Copy, Hash)]
pub enum SubjectRef<'a> {
    NamedNode(NamedNodeRef<'a>),
    BlankNode(BlankNodeRef<'a>),
    #[cfg(feature = "rdf-star")]
    Triple(&'a Triple),
}

impl<'a> SubjectRef<'a> {
    #[inline]
    pub fn is_named_node(&self) -> bool {
        matches!(self, Self::NamedNode(_))
    }

    #[inline]
    pub fn is_blank_node(&self) -> bool {
        matches!(self, Self::BlankNode(_))
    }

    #[cfg(feature = "rdf-star")]
    #[inline]
    pub fn is_triple(&self) -> bool {
        matches!(self, Self::Triple(_))
    }

    #[inline]
    pub fn into_owned(self) -> Subject {
        match self {
            Self::NamedNode(node) => Subject::NamedNode(node.into_owned()),
            Self::BlankNode(node) => Subject::BlankNode(node.into_owned()),
            #[cfg(feature = "rdf-star")]
            Self::Triple(triple) => Subject::Triple(Box::new(triple.clone())),
        }
    }
}

impl fmt::Display for SubjectRef<'_> {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::NamedNode(node) => node.fmt(f),
            Self::BlankNode(node) => node.fmt(f),
            #[cfg(feature = "rdf-star")]
            Self::Triple(triple) => write!(f, "<<{triple}>>"),
        }
    }
}

impl<'a> From<NamedNodeRef<'a>> for SubjectRef<'a> {
    #[inline]
    fn from(node: NamedNodeRef<'a>) -> Self {
        Self::NamedNode(node)
    }
}

impl<'a> From<&'a NamedNode> for SubjectRef<'a> {
    #[inline]
    fn from(node: &'a NamedNode) -> Self {
        node.as_ref().into()
    }
}

impl<'a> From<BlankNodeRef<'a>> for SubjectRef<'a> {
    #[inline]
    fn from(node: BlankNodeRef<'a>) -> Self {
        Self::BlankNode(node)
    }
}

impl<'a> From<&'a BlankNode> for SubjectRef<'a> {
    #[inline]
    fn from(node: &'a BlankNode) -> Self {
        node.as_ref().into()
    }
}

#[cfg(feature = "rdf-star")]
impl<'a> From<&'a Triple> for SubjectRef<'a> {
    #[inline]
    fn from(node: &'a Triple) -> Self {
        Self::Triple(node)
    }
}

impl<'a> From<&'a Subject> for SubjectRef<'a> {
    #[inline]
    fn from(node: &'a Subject) -> Self {
        node.as_ref()
    }
}

impl<'a> From<SubjectRef<'a>> for Subject {
    #[inline]
    fn from(node: SubjectRef<'a>) -> Self {
        node.into_owned()
    }
}

impl<'a> From<NamedOrBlankNodeRef<'a>> for SubjectRef<'a> {
    #[inline]
    fn from(node: NamedOrBlankNodeRef<'a>) -> Self {
        match node {
            NamedOrBlankNodeRef::NamedNode(node) => node.into(),
            NamedOrBlankNodeRef::BlankNode(node) => node.into(),
        }
    }
}

impl<'a> From<&'a NamedOrBlankNode> for SubjectRef<'a> {
    #[inline]
    fn from(node: &'a NamedOrBlankNode) -> Self {
        node.as_ref().into()
    }
}

/// An owned RDF [term](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-term)
/// It is the union of [IRIs](https://www.w3.org/TR/rdf11-concepts/#dfn-iri), [blank nodes](https://www.w3.org/TR/rdf11-concepts/#dfn-blank-node), [literals](https://www.w3.org/TR/rdf11-concepts/#dfn-literal) and [triples](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple) (if the `rdf-star` feature is enabled).
#[derive(Eq, PartialEq, Debug, Clone, Hash)]
pub enum Term {
    NamedNode(NamedNode),
    BlankNode(BlankNode),
    Literal(Literal),
    #[cfg(feature = "rdf-star")]
    Triple(Box<Triple>),
}

impl Term {
    #[inline]
    pub fn is_named_node(&self) -> bool {
        self.as_ref().is_named_node()
    }

    #[inline]
    pub fn is_blank_node(&self) -> bool {
        self.as_ref().is_blank_node()
    }

    #[inline]
    pub fn is_literal(&self) -> bool {
        self.as_ref().is_literal()
    }

    #[cfg(feature = "rdf-star")]
    #[inline]
    pub fn is_triple(&self) -> bool {
        self.as_ref().is_triple()
    }

    #[inline]
    pub fn as_ref(&self) -> TermRef<'_> {
        match self {
            Self::NamedNode(node) => TermRef::NamedNode(node.as_ref()),
            Self::BlankNode(node) => TermRef::BlankNode(node.as_ref()),
            Self::Literal(literal) => TermRef::Literal(literal.as_ref()),
            #[cfg(feature = "rdf-star")]
            Self::Triple(triple) => TermRef::Triple(triple),
        }
    }
}

impl fmt::Display for Term {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.as_ref().fmt(f)
    }
}

impl From<NamedNode> for Term {
    #[inline]
    fn from(node: NamedNode) -> Self {
        Self::NamedNode(node)
    }
}

impl From<NamedNodeRef<'_>> for Term {
    #[inline]
    fn from(node: NamedNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

impl From<BlankNode> for Term {
    #[inline]
    fn from(node: BlankNode) -> Self {
        Self::BlankNode(node)
    }
}

impl From<BlankNodeRef<'_>> for Term {
    #[inline]
    fn from(node: BlankNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

impl From<Literal> for Term {
    #[inline]
    fn from(literal: Literal) -> Self {
        Self::Literal(literal)
    }
}

impl From<LiteralRef<'_>> for Term {
    #[inline]
    fn from(literal: LiteralRef<'_>) -> Self {
        literal.into_owned().into()
    }
}

#[cfg(feature = "rdf-star")]
impl From<Triple> for Term {
    #[inline]
    fn from(triple: Triple) -> Self {
        Self::Triple(Box::new(triple))
    }
}

#[cfg(feature = "rdf-star")]
impl From<Box<Triple>> for Term {
    #[inline]
    fn from(node: Box<Triple>) -> Self {
        Self::Triple(node)
    }
}

#[cfg(feature = "rdf-star")]
impl From<TripleRef<'_>> for Term {
    #[inline]
    fn from(triple: TripleRef<'_>) -> Self {
        triple.into_owned().into()
    }
}

impl From<NamedOrBlankNode> for Term {
    #[inline]
    fn from(node: NamedOrBlankNode) -> Self {
        match node {
            NamedOrBlankNode::NamedNode(node) => node.into(),
            NamedOrBlankNode::BlankNode(node) => node.into(),
        }
    }
}

impl From<NamedOrBlankNodeRef<'_>> for Term {
    #[inline]
    fn from(node: NamedOrBlankNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

impl From<Subject> for Term {
    #[inline]
    fn from(node: Subject) -> Self {
        match node {
            Subject::NamedNode(node) => node.into(),
            Subject::BlankNode(node) => node.into(),
            #[cfg(feature = "rdf-star")]
            Subject::Triple(triple) => Self::Triple(triple),
        }
    }
}

impl From<SubjectRef<'_>> for Term {
    #[inline]
    fn from(node: SubjectRef<'_>) -> Self {
        node.into_owned().into()
    }
}

/// A borrowed RDF [term](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-term)
/// It is the union of [IRIs](https://www.w3.org/TR/rdf11-concepts/#dfn-iri), [blank nodes](https://www.w3.org/TR/rdf11-concepts/#dfn-blank-node), [literals](https://www.w3.org/TR/rdf11-concepts/#dfn-literal) and [triples](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple) (if the `rdf-star` feature is enabled).
#[derive(Eq, PartialEq, Debug, Clone, Copy, Hash)]
pub enum TermRef<'a> {
    NamedNode(NamedNodeRef<'a>),
    BlankNode(BlankNodeRef<'a>),
    Literal(LiteralRef<'a>),
    #[cfg(feature = "rdf-star")]
    Triple(&'a Triple),
}

impl<'a> TermRef<'a> {
    #[inline]
    pub fn is_named_node(&self) -> bool {
        matches!(self, Self::NamedNode(_))
    }

    #[inline]
    pub fn is_blank_node(&self) -> bool {
        matches!(self, Self::BlankNode(_))
    }

    #[inline]
    pub fn is_literal(&self) -> bool {
        matches!(self, Self::Literal(_))
    }

    #[cfg(feature = "rdf-star")]
    #[inline]
    pub fn is_triple(&self) -> bool {
        matches!(self, Self::Triple(_))
    }

    #[inline]
    pub fn into_owned(self) -> Term {
        match self {
            Self::NamedNode(node) => Term::NamedNode(node.into_owned()),
            Self::BlankNode(node) => Term::BlankNode(node.into_owned()),
            Self::Literal(literal) => Term::Literal(literal.into_owned()),
            #[cfg(feature = "rdf-star")]
            Self::Triple(triple) => Term::Triple(Box::new(triple.clone())),
        }
    }
}

impl fmt::Display for TermRef<'_> {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::NamedNode(node) => node.fmt(f),
            Self::BlankNode(node) => node.fmt(f),
            Self::Literal(literal) => literal.fmt(f),
            #[cfg(feature = "rdf-star")]
            Self::Triple(triple) => {
                write!(f, "<<{triple}>>")
            }
        }
    }
}

impl<'a> From<NamedNodeRef<'a>> for TermRef<'a> {
    #[inline]
    fn from(node: NamedNodeRef<'a>) -> Self {
        Self::NamedNode(node)
    }
}

impl<'a> From<&'a NamedNode> for TermRef<'a> {
    #[inline]
    fn from(node: &'a NamedNode) -> Self {
        node.as_ref().into()
    }
}

impl<'a> From<BlankNodeRef<'a>> for TermRef<'a> {
    #[inline]
    fn from(node: BlankNodeRef<'a>) -> Self {
        Self::BlankNode(node)
    }
}

impl<'a> From<&'a BlankNode> for TermRef<'a> {
    #[inline]
    fn from(node: &'a BlankNode) -> Self {
        node.as_ref().into()
    }
}

impl<'a> From<LiteralRef<'a>> for TermRef<'a> {
    #[inline]
    fn from(literal: LiteralRef<'a>) -> Self {
        Self::Literal(literal)
    }
}

impl<'a> From<&'a Literal> for TermRef<'a> {
    #[inline]
    fn from(literal: &'a Literal) -> Self {
        literal.as_ref().into()
    }
}

#[cfg(feature = "rdf-star")]
impl<'a> From<&'a Triple> for TermRef<'a> {
    #[inline]
    fn from(node: &'a Triple) -> Self {
        Self::Triple(node)
    }
}

impl<'a> From<NamedOrBlankNodeRef<'a>> for TermRef<'a> {
    #[inline]
    fn from(node: NamedOrBlankNodeRef<'a>) -> Self {
        match node {
            NamedOrBlankNodeRef::NamedNode(node) => node.into(),
            NamedOrBlankNodeRef::BlankNode(node) => node.into(),
        }
    }
}

impl<'a> From<&'a NamedOrBlankNode> for TermRef<'a> {
    #[inline]
    fn from(node: &'a NamedOrBlankNode) -> Self {
        node.as_ref().into()
    }
}

impl<'a> From<SubjectRef<'a>> for TermRef<'a> {
    #[inline]
    fn from(node: SubjectRef<'a>) -> Self {
        match node {
            SubjectRef::NamedNode(node) => node.into(),
            SubjectRef::BlankNode(node) => node.into(),
            #[cfg(feature = "rdf-star")]
            SubjectRef::Triple(triple) => triple.into(),
        }
    }
}

impl<'a> From<&'a Subject> for TermRef<'a> {
    #[inline]
    fn from(node: &'a Subject) -> Self {
        node.as_ref().into()
    }
}

impl<'a> From<&'a Term> for TermRef<'a> {
    #[inline]
    fn from(node: &'a Term) -> Self {
        node.as_ref()
    }
}

impl<'a> From<TermRef<'a>> for Term {
    #[inline]
    fn from(node: TermRef<'a>) -> Self {
        node.into_owned()
    }
}

/// An owned [RDF triple](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple).
///
/// The default string formatter is returning an N-Triples, Turtle, and SPARQL compatible representation:
/// ```
/// use oxrdf::{NamedNode, Triple};
///
/// assert_eq!(
///     "<http://example.com/s> <http://example.com/p> <http://example.com/o>",
///     Triple {
///         subject: NamedNode::new("http://example.com/s")?.into(),
///         predicate: NamedNode::new("http://example.com/p")?,
///         object: NamedNode::new("http://example.com/o")?.into(),
///     }
///     .to_string()
/// );
/// # Result::<_,oxrdf::IriParseError>::Ok(())
/// ```
#[derive(Eq, PartialEq, Debug, Clone, Hash)]
pub struct Triple {
    /// The [subject](https://www.w3.org/TR/rdf11-concepts/#dfn-subject) of this triple.
    pub subject: Subject,

    /// The [predicate](https://www.w3.org/TR/rdf11-concepts/#dfn-predicate) of this triple.
    pub predicate: NamedNode,

    /// The [object](https://www.w3.org/TR/rdf11-concepts/#dfn-object) of this triple.
    pub object: Term,
}

impl Triple {
    /// Builds an RDF [triple](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple).
    #[inline]
    pub fn new(
        subject: impl Into<Subject>,
        predicate: impl Into<NamedNode>,
        object: impl Into<Term>,
    ) -> Self {
        Self {
            subject: subject.into(),
            predicate: predicate.into(),
            object: object.into(),
        }
    }

    /// Builds an RDF [triple](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple).
    #[inline]
    pub fn new_from_terms(
        subject: impl Into<Term>,
        predicate: impl Into<Term>,
        object: impl Into<Term>,
    ) -> Result<Self, TripleConstructionError> {
        let subject: Result<Subject, TryFromTermError> = subject.into().try_into();
        let predicate: Result<NamedNode, TryFromTermError> = predicate.into().try_into();
        if let (Ok(subject), Ok(predicate)) = (subject.clone(), predicate.clone()) {
            Ok(Self {
                subject,
                predicate,
                object: object.into(),
            })
        } else {
            Err(TripleConstructionError {
                subject,
                predicate,
                object: object.into(),
            })
        }
    }

    /// Encodes that this triple is in an [RDF dataset](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-dataset).
    #[inline]
    pub fn in_graph(self, graph_name: impl Into<GraphName>) -> Quad {
        Quad {
            subject: self.subject,
            predicate: self.predicate,
            object: self.object,
            graph_name: graph_name.into(),
        }
    }

    #[inline]
    pub fn as_ref(&self) -> TripleRef<'_> {
        TripleRef {
            subject: self.subject.as_ref(),
            predicate: self.predicate.as_ref(),
            object: self.object.as_ref(),
        }
    }
}

impl fmt::Display for Triple {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.as_ref().fmt(f)
    }
}

#[cfg(feature = "rdf-star")]
impl TryFrom<Term> for Box<Triple> {
    type Error = TryFromTermError;

    #[inline]
    fn try_from(term: Term) -> Result<Self, Self::Error> {
        if let Term::Triple(node) = term {
            Ok(node)
        } else {
            Err(TryFromTermError {
                term,
                target: "Box<Triple>",
            })
        }
    }
}

/// A borrowed [RDF triple](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple).
///
/// The default string formatter is returning an N-Triples, Turtle, and SPARQL compatible representation:
/// ```
/// use oxrdf::{NamedNodeRef, TripleRef};
///
/// assert_eq!(
///     "<http://example.com/s> <http://example.com/p> <http://example.com/o>",
///     TripleRef {
///         subject: NamedNodeRef::new("http://example.com/s")?.into(),
///         predicate: NamedNodeRef::new("http://example.com/p")?,
///         object: NamedNodeRef::new("http://example.com/o")?.into(),
///     }
///     .to_string()
/// );
/// # Result::<_,oxrdf::IriParseError>::Ok(())
/// ```

#[derive(Eq, PartialEq, Debug, Clone, Copy, Hash)]
pub struct TripleRef<'a> {
    /// The [subject](https://www.w3.org/TR/rdf11-concepts/#dfn-subject) of this triple.
    pub subject: SubjectRef<'a>,

    /// The [predicate](https://www.w3.org/TR/rdf11-concepts/#dfn-predicate) of this triple.
    pub predicate: NamedNodeRef<'a>,

    /// The [object](https://www.w3.org/TR/rdf11-concepts/#dfn-object) of this triple.
    pub object: TermRef<'a>,
}

impl<'a> TripleRef<'a> {
    /// Builds an RDF [triple](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple).
    #[inline]
    pub fn new(
        subject: impl Into<SubjectRef<'a>>,
        predicate: impl Into<NamedNodeRef<'a>>,
        object: impl Into<TermRef<'a>>,
    ) -> Self {
        Self {
            subject: subject.into(),
            predicate: predicate.into(),
            object: object.into(),
        }
    }

    /// Encodes that this triple is in an [RDF dataset](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-dataset).
    #[inline]
    pub fn in_graph(self, graph_name: impl Into<GraphNameRef<'a>>) -> QuadRef<'a> {
        QuadRef {
            subject: self.subject,
            predicate: self.predicate,
            object: self.object,
            graph_name: graph_name.into(),
        }
    }

    #[inline]
    pub fn into_owned(self) -> Triple {
        Triple {
            subject: self.subject.into_owned(),
            predicate: self.predicate.into_owned(),
            object: self.object.into_owned(),
        }
    }
}

impl fmt::Display for TripleRef<'_> {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{} {} {}", self.subject, self.predicate, self.object)
    }
}

impl<'a> From<&'a Triple> for TripleRef<'a> {
    #[inline]
    fn from(triple: &'a Triple) -> Self {
        triple.as_ref()
    }
}

impl<'a> From<TripleRef<'a>> for Triple {
    #[inline]
    fn from(triple: TripleRef<'a>) -> Self {
        triple.into_owned()
    }
}

/// A possible owned graph name.
/// It is the union of [IRIs](https://www.w3.org/TR/rdf11-concepts/#dfn-iri), [blank nodes](https://www.w3.org/TR/rdf11-concepts/#dfn-blank-node), and the [default graph name](https://www.w3.org/TR/rdf11-concepts/#dfn-default-graph).
#[derive(Eq, PartialEq, Debug, Clone, Hash, Default)]
pub enum GraphName {
    NamedNode(NamedNode),
    BlankNode(BlankNode),
    #[default]
    DefaultGraph,
}

impl GraphName {
    #[inline]
    pub fn is_named_node(&self) -> bool {
        self.as_ref().is_named_node()
    }

    #[inline]
    pub fn is_blank_node(&self) -> bool {
        self.as_ref().is_blank_node()
    }

    #[inline]
    pub fn is_default_graph(&self) -> bool {
        self.as_ref().is_default_graph()
    }

    #[inline]
    pub fn as_ref(&self) -> GraphNameRef<'_> {
        match self {
            Self::NamedNode(node) => GraphNameRef::NamedNode(node.as_ref()),
            Self::BlankNode(node) => GraphNameRef::BlankNode(node.as_ref()),
            Self::DefaultGraph => GraphNameRef::DefaultGraph,
        }
    }
}

impl fmt::Display for GraphName {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.as_ref().fmt(f)
    }
}

impl From<NamedNode> for GraphName {
    #[inline]
    fn from(node: NamedNode) -> Self {
        Self::NamedNode(node)
    }
}

impl From<NamedNodeRef<'_>> for GraphName {
    #[inline]
    fn from(node: NamedNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

impl From<BlankNode> for GraphName {
    #[inline]
    fn from(node: BlankNode) -> Self {
        Self::BlankNode(node)
    }
}

impl From<BlankNodeRef<'_>> for GraphName {
    #[inline]
    fn from(node: BlankNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

impl From<NamedOrBlankNode> for GraphName {
    #[inline]
    fn from(node: NamedOrBlankNode) -> Self {
        match node {
            NamedOrBlankNode::NamedNode(node) => node.into(),
            NamedOrBlankNode::BlankNode(node) => node.into(),
        }
    }
}

impl From<NamedOrBlankNodeRef<'_>> for GraphName {
    #[inline]
    fn from(node: NamedOrBlankNodeRef<'_>) -> Self {
        node.into_owned().into()
    }
}

/// A possible borrowed graph name.
/// It is the union of [IRIs](https://www.w3.org/TR/rdf11-concepts/#dfn-iri), [blank nodes](https://www.w3.org/TR/rdf11-concepts/#dfn-blank-node), and the [default graph name](https://www.w3.org/TR/rdf11-concepts/#dfn-default-graph).
#[derive(Eq, PartialEq, Debug, Clone, Copy, Hash, Default)]
pub enum GraphNameRef<'a> {
    NamedNode(NamedNodeRef<'a>),
    BlankNode(BlankNodeRef<'a>),
    #[default]
    DefaultGraph,
}

impl<'a> GraphNameRef<'a> {
    #[inline]
    pub fn is_named_node(&self) -> bool {
        matches!(self, Self::NamedNode(_))
    }

    #[inline]
    pub fn is_blank_node(&self) -> bool {
        matches!(self, Self::BlankNode(_))
    }

    #[inline]
    pub fn is_default_graph(&self) -> bool {
        matches!(self, Self::DefaultGraph)
    }

    #[inline]
    pub fn into_owned(self) -> GraphName {
        match self {
            Self::NamedNode(node) => GraphName::NamedNode(node.into_owned()),
            Self::BlankNode(node) => GraphName::BlankNode(node.into_owned()),
            Self::DefaultGraph => GraphName::DefaultGraph,
        }
    }
}

impl fmt::Display for GraphNameRef<'_> {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::NamedNode(node) => node.fmt(f),
            Self::BlankNode(node) => node.fmt(f),
            Self::DefaultGraph => f.write_str("DEFAULT"),
        }
    }
}

impl<'a> From<NamedNodeRef<'a>> for GraphNameRef<'a> {
    #[inline]
    fn from(node: NamedNodeRef<'a>) -> Self {
        Self::NamedNode(node)
    }
}

impl<'a> From<&'a NamedNode> for GraphNameRef<'a> {
    #[inline]
    fn from(node: &'a NamedNode) -> Self {
        node.as_ref().into()
    }
}

impl<'a> From<BlankNodeRef<'a>> for GraphNameRef<'a> {
    #[inline]
    fn from(node: BlankNodeRef<'a>) -> Self {
        Self::BlankNode(node)
    }
}

impl<'a> From<&'a BlankNode> for GraphNameRef<'a> {
    #[inline]
    fn from(node: &'a BlankNode) -> Self {
        node.as_ref().into()
    }
}

impl<'a> From<NamedOrBlankNodeRef<'a>> for GraphNameRef<'a> {
    #[inline]
    fn from(node: NamedOrBlankNodeRef<'a>) -> Self {
        match node {
            NamedOrBlankNodeRef::NamedNode(node) => node.into(),
            NamedOrBlankNodeRef::BlankNode(node) => node.into(),
        }
    }
}

impl<'a> From<&'a NamedOrBlankNode> for GraphNameRef<'a> {
    #[inline]
    fn from(node: &'a NamedOrBlankNode) -> Self {
        node.as_ref().into()
    }
}

impl<'a> From<&'a GraphName> for GraphNameRef<'a> {
    #[inline]
    fn from(node: &'a GraphName) -> Self {
        node.as_ref()
    }
}

impl<'a> From<GraphNameRef<'a>> for GraphName {
    #[inline]
    fn from(node: GraphNameRef<'a>) -> Self {
        node.into_owned()
    }
}

/// An owned [triple](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple) in an [RDF dataset](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-dataset).
///
/// The default string formatter is returning an N-Quads compatible representation:
/// ```
/// use oxrdf::{Quad, NamedNode};
///
/// assert_eq!(
///     "<http://example.com/s> <http://example.com/p> <http://example.com/o> <http://example.com/g>",
///     Quad {
///         subject: NamedNode::new("http://example.com/s")?.into(),
///         predicate: NamedNode::new("http://example.com/p")?,
///         object: NamedNode::new("http://example.com/o")?.into(),
///         graph_name: NamedNode::new("http://example.com/g")?.into(),
///     }.to_string()
/// );
/// # Result::<_,oxrdf::IriParseError>::Ok(())
/// ```
#[derive(Eq, PartialEq, Debug, Clone, Hash)]
pub struct Quad {
    /// The [subject](https://www.w3.org/TR/rdf11-concepts/#dfn-subject) of this triple.
    pub subject: Subject,

    /// The [predicate](https://www.w3.org/TR/rdf11-concepts/#dfn-predicate) of this triple.
    pub predicate: NamedNode,

    /// The [object](https://www.w3.org/TR/rdf11-concepts/#dfn-object) of this triple.
    pub object: Term,

    /// The name of the RDF [graph](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-graph) in which the triple is.
    pub graph_name: GraphName,
}

impl Quad {
    /// Builds an RDF [triple](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple) in an [RDF dataset](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-dataset).
    #[inline]
    pub fn new(
        subject: impl Into<Subject>,
        predicate: impl Into<NamedNode>,
        object: impl Into<Term>,
        graph_name: impl Into<GraphName>,
    ) -> Self {
        Self {
            subject: subject.into(),
            predicate: predicate.into(),
            object: object.into(),
            graph_name: graph_name.into(),
        }
    }

    #[inline]
    pub fn as_ref(&self) -> QuadRef<'_> {
        QuadRef {
            subject: self.subject.as_ref(),
            predicate: self.predicate.as_ref(),
            object: self.object.as_ref(),
            graph_name: self.graph_name.as_ref(),
        }
    }
}

impl fmt::Display for Quad {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.as_ref().fmt(f)
    }
}

impl From<Quad> for Triple {
    #[inline]
    fn from(quad: Quad) -> Self {
        Self {
            subject: quad.subject,
            predicate: quad.predicate,
            object: quad.object,
        }
    }
}

/// A borrowed [triple](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple) in an [RDF dataset](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-dataset).
///
/// The default string formatter is returning an N-Quads compatible representation:
/// ```
/// use oxrdf::{QuadRef, NamedNodeRef};
///
/// assert_eq!(
///     "<http://example.com/s> <http://example.com/p> <http://example.com/o> <http://example.com/g>",
///     QuadRef {
///         subject: NamedNodeRef::new("http://example.com/s")?.into(),
///         predicate: NamedNodeRef::new("http://example.com/p")?,
///         object: NamedNodeRef::new("http://example.com/o")?.into(),
///         graph_name: NamedNodeRef::new("http://example.com/g")?.into(),
///     }.to_string()
/// );
/// # Result::<_,oxrdf::IriParseError>::Ok(())
/// ```
#[derive(Eq, PartialEq, Debug, Clone, Copy, Hash)]
pub struct QuadRef<'a> {
    /// The [subject](https://www.w3.org/TR/rdf11-concepts/#dfn-subject) of this triple.
    pub subject: SubjectRef<'a>,

    /// The [predicate](https://www.w3.org/TR/rdf11-concepts/#dfn-predicate) of this triple.
    pub predicate: NamedNodeRef<'a>,

    /// The [object](https://www.w3.org/TR/rdf11-concepts/#dfn-object) of this triple.
    pub object: TermRef<'a>,

    /// The name of the RDF [graph](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-graph) in which the triple is.
    pub graph_name: GraphNameRef<'a>,
}

impl<'a> QuadRef<'a> {
    /// Builds an RDF [triple](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-triple) in an [RDF dataset](https://www.w3.org/TR/rdf11-concepts/#dfn-rdf-dataset).
    #[inline]
    pub fn new(
        subject: impl Into<SubjectRef<'a>>,
        predicate: impl Into<NamedNodeRef<'a>>,
        object: impl Into<TermRef<'a>>,
        graph_name: impl Into<GraphNameRef<'a>>,
    ) -> Self {
        Self {
            subject: subject.into(),
            predicate: predicate.into(),
            object: object.into(),
            graph_name: graph_name.into(),
        }
    }

    #[inline]
    pub fn into_owned(self) -> Quad {
        Quad {
            subject: self.subject.into_owned(),
            predicate: self.predicate.into_owned(),
            object: self.object.into_owned(),
            graph_name: self.graph_name.into_owned(),
        }
    }
}

impl fmt::Display for QuadRef<'_> {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if self.graph_name.is_default_graph() {
            write!(f, "{} {} {}", self.subject, self.predicate, self.object)
        } else {
            write!(
                f,
                "{} {} {} {}",
                self.subject, self.predicate, self.object, self.graph_name
            )
        }
    }
}

impl<'a> From<QuadRef<'a>> for TripleRef<'a> {
    #[inline]
    fn from(quad: QuadRef<'a>) -> Self {
        Self {
            subject: quad.subject,
            predicate: quad.predicate,
            object: quad.object,
        }
    }
}

impl<'a> From<&'a Quad> for QuadRef<'a> {
    #[inline]
    fn from(quad: &'a Quad) -> Self {
        quad.as_ref()
    }
}

impl<'a> From<QuadRef<'a>> for Quad {
    #[inline]
    fn from(quad: QuadRef<'a>) -> Self {
        quad.into_owned()
    }
}

#[cfg(feature = "rdf-star")]
#[cfg(test)]
mod tests {
    #![allow(clippy::panic_in_result_fn)]

    use super::*;

    #[test]
    fn casting_triple() {
        let triple = Triple {
            subject: NamedNode::new("http://example.org/s").unwrap().into(),
            predicate: NamedNode::new("http://example.org/p").unwrap(),
            object: NamedNode::new("http://example.org/o").unwrap().into(),
        };
        let triple_box = Box::new(triple);

        let t: Result<Box<Triple>, TryFromTermError> = Term::Triple(triple_box.clone()).try_into();
        assert_eq!(t.unwrap(), triple_box.clone());

        let literal: Result<Box<Triple>, TryFromTermError> =
            Term::Literal(Literal::new_simple_literal("Hello World!")).try_into();
        let literal_err = literal.unwrap_err();
        assert_eq!(
            literal_err.term,
            Term::Literal(Literal::new_simple_literal("Hello World!"))
        );
        assert_eq!(literal_err.target, "Box<Triple>");
        assert_eq!(
            literal_err.to_string(),
            "\"Hello World!\" can not be converted to a Box<Triple>"
        );
        assert_eq!(
            Term::from(literal_err),
            Term::Literal(Literal::new_simple_literal("Hello World!"))
        );

        let bnode: Result<Box<Triple>, TryFromTermError> =
            Term::BlankNode(BlankNode::new_from_unique_id(0x42)).try_into();
        let bnode_err = bnode.unwrap_err();
        assert_eq!(
            bnode_err.term,
            Term::BlankNode(BlankNode::new_from_unique_id(0x42))
        );
        assert_eq!(bnode_err.target, "Box<Triple>");
        assert_eq!(
            bnode_err.to_string(),
            "_:42 can not be converted to a Box<Triple>"
        );
        assert_eq!(
            Term::from(bnode_err),
            Term::BlankNode(BlankNode::new_from_unique_id(0x42))
        );

        let named_node: Result<Box<Triple>, TryFromTermError> =
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap()).try_into();
        let named_node_err = named_node.unwrap_err();
        assert_eq!(
            named_node_err.term,
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap())
        );
        assert_eq!(named_node_err.target, "Box<Triple>");
        assert_eq!(
            named_node_err.to_string(),
            "<http://example.org/test> can not be converted to a Box<Triple>"
        );
        assert_eq!(
            Term::from(named_node_err),
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap())
        );
    }

    #[test]
    fn constructing_triple() {
        use super::*;

        let optional_triple = Triple::new_from_terms(
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap()),
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap()),
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap()),
        );

        let optional_triple_2 = Triple::new_from_terms(
            NamedNode::new("http://example.org/test").unwrap(),
            NamedNode::new("http://example.org/test").unwrap(),
            NamedNode::new("http://example.org/test").unwrap(),
        );

        let bad_triple: Result<Triple, TripleConstructionError> = Triple::new_from_terms(
            Term::Literal(Literal::new_simple_literal("abc123")),
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap()),
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap()),
        );

        let bad_triple_2 = Triple::new_from_terms(
            Term::Literal(Literal::new_simple_literal("abc123")),
            NamedNode::new("http://example.org/test").unwrap(),
            NamedNode::new("http://example.org/test").unwrap(),
        );

        let bad_triple_3 = Triple::new_from_terms(
            Term::Literal(Literal::new_simple_literal("abc123")),
            BlankNode::new_from_unique_id(0x42),
            NamedNode::new("http://example.org/test").unwrap(),
        );

        let triple: Triple = Triple::new(
            Subject::NamedNode(NamedNode::new("http://example.org/test").unwrap()),
            NamedNode::new("http://example.org/test").unwrap(),
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap()),
        );

        let triple_2: Triple = Triple::new(
            NamedNode::new("http://example.org/test").unwrap(),
            NamedNode::new("http://example.org/test").unwrap(),
            NamedNode::new("http://example.org/test").unwrap(),
        );

        let unwrapped = optional_triple.unwrap();

        assert_eq!(unwrapped, triple);
        assert_eq!(unwrapped, triple_2.clone());
        assert_eq!(optional_triple_2.unwrap(), triple_2);
        let bad_triple_err = bad_triple.unwrap_err();
        assert_eq!(
            bad_triple_err.to_string(),
            "subject: [\"abc123\" can not be converted to a Subject]"
        );
        assert_eq!(
            bad_triple_err.subject.clone().unwrap_err().clone().term,
            Term::Literal(Literal::new_simple_literal("abc123"))
        );
        assert_eq!(
            bad_triple_err.subject.clone().unwrap_err().clone().target,
            "Subject"
        );
        assert_eq!(
            bad_triple_err.subject.unwrap_err().clone().to_string(),
            "\"abc123\" can not be converted to a Subject"
        );

        assert_eq!(bad_triple_2.is_err(), true);
        let bad_triple_2_err = bad_triple_2.unwrap_err();
        assert_eq!(
            bad_triple_2_err.to_string(),
            "subject: [\"abc123\" can not be converted to a Subject]"
        );
        assert_eq!(
            bad_triple_2_err.subject.clone().unwrap_err().clone().term,
            Term::Literal(Literal::new_simple_literal("abc123"))
        );
        assert_eq!(
            bad_triple_2_err.subject.clone().unwrap_err().clone().target,
            "Subject"
        );
        assert_eq!(
            bad_triple_2_err.subject.unwrap_err().clone().to_string(),
            "\"abc123\" can not be converted to a Subject"
        );
        assert_eq!(
            bad_triple_2_err.predicate.unwrap(),
            NamedNode::new("http://example.org/test").unwrap()
        );
        assert_eq!(
            bad_triple_2_err.object,
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap())
        );

        assert_eq!(bad_triple_3.is_err(), true);
        let bad_triple_3_err = bad_triple_3.unwrap_err();
        assert_eq!(bad_triple_3_err.to_string(), "subject: [\"abc123\" can not be converted to a Subject], predicate: [_:42 can not be converted to a NamedNode]");
        assert_eq!(
            bad_triple_3_err.subject.clone().unwrap_err().clone().term,
            Term::Literal(Literal::new_simple_literal("abc123"))
        );
        assert_eq!(
            bad_triple_3_err.subject.clone().unwrap_err().clone().target,
            "Subject"
        );
        assert_eq!(
            bad_triple_3_err.subject.unwrap_err().clone().to_string(),
            "\"abc123\" can not be converted to a Subject"
        );
        assert_eq!(
            bad_triple_3_err.predicate.clone().unwrap_err().clone().term,
            Term::BlankNode(BlankNode::new_from_unique_id(0x42))
        );
        assert_eq!(
            bad_triple_3_err
                .predicate
                .clone()
                .unwrap_err()
                .clone()
                .target,
            "NamedNode"
        );
        assert_eq!(
            bad_triple_3_err.predicate.unwrap_err().clone().to_string(),
            "_:42 can not be converted to a NamedNode"
        );
    }

    #[test]
    fn casting_subject() {
        let triple = Triple {
            subject: NamedNode::new("http://example.org/s").unwrap().into(),
            predicate: NamedNode::new("http://example.org/p").unwrap(),
            object: NamedNode::new("http://example.org/o").unwrap().into(),
        };
        let triple_box = Box::new(triple);

        let t: Result<Subject, TryFromTermError> = Term::Triple(triple_box.clone()).try_into();
        assert_eq!(t.unwrap(), Subject::Triple(triple_box.clone()));

        let literal: Result<Subject, TryFromTermError> =
            Term::Literal(Literal::new_simple_literal("Hello World!")).try_into();
        assert_eq!(literal.is_err(), true);
        assert_eq!(literal.is_err(), true);

        let bnode: Result<Subject, TryFromTermError> =
            Term::BlankNode(BlankNode::new_from_unique_id(0x42)).try_into();
        assert_eq!(
            bnode.unwrap(),
            Subject::BlankNode(BlankNode::new_from_unique_id(0x42))
        );

        let named_node: Result<Subject, TryFromTermError> =
            Term::NamedNode(NamedNode::new("http://example.org/test").unwrap()).try_into();
        assert_eq!(
            named_node.unwrap(),
            Subject::NamedNode(NamedNode::new("http://example.org/test").unwrap())
        );
    }
}