diff --git a/lib/src/store/numeric_encoder.rs b/lib/src/store/numeric_encoder.rs
index 6b639d3f..2cd18cad 100644
--- a/lib/src/store/numeric_encoder.rs
+++ b/lib/src/store/numeric_encoder.rs
@@ -12,7 +12,7 @@ use siphasher::sip128::{Hasher128, SipHasher24};
 use std::collections::HashMap;
 use std::hash::Hash;
 use std::hash::Hasher;
-use std::io::Read;
+use std::io::{Cursor, Read};
 use std::mem::size_of;
 use std::str;
 
@@ -800,6 +800,30 @@ pub fn write_gosp_quad(sink: &mut Vec<u8>, quad: &EncodedQuad) {
     write_term(sink, quad.predicate);
 }
 
+#[derive(Clone, Copy)]
+pub enum QuadEncoding {
+    SPOG,
+    POSG,
+    OSPG,
+    GSPO,
+    GPOS,
+    GOSP,
+}
+
+impl QuadEncoding {
+    pub fn decode(self, buffer: &[u8]) -> Result<EncodedQuad> {
+        let mut cursor = Cursor::new(&buffer);
+        match self {
+            QuadEncoding::SPOG => cursor.read_spog_quad(),
+            QuadEncoding::POSG => cursor.read_posg_quad(),
+            QuadEncoding::OSPG => cursor.read_ospg_quad(),
+            QuadEncoding::GSPO => cursor.read_gspo_quad(),
+            QuadEncoding::GPOS => cursor.read_gpos_quad(),
+            QuadEncoding::GOSP => cursor.read_gosp_quad(),
+        }
+    }
+}
+
 pub trait StrLookup {
     fn get_str(&self, id: StrHash) -> Result<Option<String>>;
 }
diff --git a/lib/src/store/rocksdb.rs b/lib/src/store/rocksdb.rs
index 42b98470..1aea566d 100644
--- a/lib/src/store/rocksdb.rs
+++ b/lib/src/store/rocksdb.rs
@@ -2,10 +2,9 @@ use crate::model::*;
 use crate::sparql::{GraphPattern, PreparedQuery, QueryOptions, SimplePreparedQuery};
 use crate::store::numeric_encoder::*;
 use crate::store::{load_dataset, load_graph, ReadableEncodedStore, WritableEncodedStore};
-use crate::{DatasetSyntax, Error, GraphSyntax, Result};
+use crate::{DatasetSyntax, GraphSyntax, Result};
 use rocksdb::*;
-use std::io::{BufRead, Cursor};
-use std::iter::{empty, once};
+use std::io::BufRead;
 use std::mem::take;
 use std::path::Path;
 use std::str;
@@ -91,7 +90,7 @@ impl RocksDbStore {
             db: Arc::new(DB::open_cf(&options, path, &COLUMN_FAMILIES)?),
         };
 
-        let mut transaction = new.handle()?.auto_transaction();
+        let mut transaction = new.handle().auto_transaction();
         transaction.set_first_strings()?;
         transaction.commit()?;
 
@@ -128,7 +127,7 @@ impl RocksDbStore {
         predicate: Option<&NamedNode>,
         object: Option<&Term>,
         graph_name: Option<Option<&NamedOrBlankNode>>,
-    ) -> Box<dyn Iterator<Item = Result<Quad>> + 'a>
+    ) -> impl Iterator<Item = Result<Quad>> + 'a
     where
         Self: 'a,
     {
@@ -136,16 +135,15 @@ impl RocksDbStore {
         let predicate = predicate.map(|p| p.into());
         let object = object.map(|o| o.into());
         let graph_name = graph_name.map(|g| g.map_or(ENCODED_DEFAULT_GRAPH, |g| g.into()));
-        Box::new(
-            self.encoded_quads_for_pattern(subject, predicate, object, graph_name)
-                .map(move |quad| self.decode_quad(&quad?)),
-        )
+        self.handle()
+            .encoded_quads_for_pattern(subject, predicate, object, graph_name)
+            .map(move |quad| self.decode_quad(&quad?))
     }
 
     /// Checks if this store contains a given quad
     pub fn contains(&self, quad: &Quad) -> Result<bool> {
         let quad = quad.into();
-        self.handle()?.contains(&quad)
+        self.handle().contains(&quad)
     }
 
     /// Executes a transaction.
@@ -158,7 +156,7 @@ impl RocksDbStore {
         &'a self,
         f: impl FnOnce(&mut RocksDbTransaction<'a>) -> Result<()>,
     ) -> Result<()> {
-        let mut transaction = self.handle()?.transaction();
+        let mut transaction = self.handle().transaction();
         f(&mut transaction)?;
         transaction.commit()
     }
@@ -176,7 +174,7 @@ impl RocksDbStore {
         to_graph_name: Option<&NamedOrBlankNode>,
         base_iri: Option<&str>,
     ) -> Result<()> {
-        let mut transaction = self.handle()?.auto_transaction();
+        let mut transaction = self.handle().auto_transaction();
         load_graph(&mut transaction, reader, syntax, to_graph_name, base_iri)?;
         transaction.commit()
     }
@@ -193,14 +191,14 @@ impl RocksDbStore {
         syntax: DatasetSyntax,
         base_iri: Option<&str>,
     ) -> Result<()> {
-        let mut transaction = self.handle()?.auto_transaction();
+        let mut transaction = self.handle().auto_transaction();
         load_dataset(&mut transaction, reader, syntax, base_iri)?;
         transaction.commit()
     }
 
     /// Adds a quad to this store.
     pub fn insert(&self, quad: &Quad) -> Result<()> {
-        let mut transaction = self.handle()?.auto_transaction();
+        let mut transaction = self.handle().auto_transaction();
         let quad = transaction.encode_quad(quad)?;
         transaction.insert_encoded(&quad)?;
         transaction.commit()
@@ -208,23 +206,23 @@ impl RocksDbStore {
 
     /// Removes a quad from this store.
     pub fn remove(&self, quad: &Quad) -> Result<()> {
-        let mut transaction = self.handle()?.auto_transaction();
+        let mut transaction = self.handle().auto_transaction();
         let quad = quad.into();
         transaction.remove_encoded(&quad)?;
         transaction.commit()
     }
 
-    fn handle<'a>(&'a self) -> Result<RocksDbStoreHandle<'a>> {
-        Ok(RocksDbStoreHandle {
+    fn handle(&self) -> RocksDbStoreHandle<'_> {
+        RocksDbStoreHandle {
             db: &self.db,
-            id2str_cf: get_cf(&self.db, ID2STR_CF)?,
-            spog_cf: get_cf(&self.db, SPOG_CF)?,
-            posg_cf: get_cf(&self.db, POSG_CF)?,
-            ospg_cf: get_cf(&self.db, OSPG_CF)?,
-            gspo_cf: get_cf(&self.db, GSPO_CF)?,
-            gpos_cf: get_cf(&self.db, GPOS_CF)?,
-            gosp_cf: get_cf(&self.db, GOSP_CF)?,
-        })
+            id2str_cf: get_cf(&self.db, ID2STR_CF),
+            spog_cf: get_cf(&self.db, SPOG_CF),
+            posg_cf: get_cf(&self.db, POSG_CF),
+            ospg_cf: get_cf(&self.db, OSPG_CF),
+            gspo_cf: get_cf(&self.db, GSPO_CF),
+            gpos_cf: get_cf(&self.db, GPOS_CF),
+            gosp_cf: get_cf(&self.db, GOSP_CF),
+        }
     }
 }
 
@@ -232,7 +230,7 @@ impl StrLookup for RocksDbStore {
     fn get_str(&self, id: StrHash) -> Result<Option<String>> {
         Ok(self
             .db
-            .get_cf(get_cf(&self.db, ID2STR_CF)?, &id.to_be_bytes())?
+            .get_cf(get_cf(&self.db, ID2STR_CF), &id.to_be_bytes())?
             .map(String::from_utf8)
             .transpose()?)
     }
@@ -246,116 +244,108 @@ impl ReadableEncodedStore for RocksDbStore {
         object: Option<EncodedTerm>,
         graph_name: Option<EncodedTerm>,
     ) -> Box<dyn Iterator<Item = Result<EncodedQuad>> + 'a> {
-        let handle = match self.handle() {
-            Ok(handle) => handle,
-            Err(error) => return Box::new(once(Err(error))),
-        };
+        Box::new(
+            self.handle()
+                .encoded_quads_for_pattern(subject, predicate, object, graph_name),
+        )
+    }
+}
+
+impl<'a> RocksDbStoreHandle<'a> {
+    fn transaction(&self) -> RocksDbTransaction<'a> {
+        RocksDbTransaction {
+            inner: RocksDbInnerTransaction {
+                handle: self.clone(),
+                batch: WriteBatch::default(),
+                buffer: Vec::default(),
+            },
+        }
+    }
+
+    fn auto_transaction(&self) -> RocksDbAutoTransaction<'a> {
+        RocksDbAutoTransaction {
+            inner: RocksDbInnerTransaction {
+                handle: self.clone(),
+                batch: WriteBatch::default(),
+                buffer: Vec::default(),
+            },
+        }
+    }
+
+    fn contains(&self, quad: &EncodedQuad) -> Result<bool> {
+        let mut buffer = Vec::with_capacity(4 * WRITTEN_TERM_MAX_SIZE);
+        write_spog_quad(&mut buffer, quad);
+        Ok(self.db.get_pinned_cf(self.spog_cf, &buffer)?.is_some())
+    }
+
+    fn encoded_quads_for_pattern(
+        &self,
+        subject: Option<EncodedTerm>,
+        predicate: Option<EncodedTerm>,
+        object: Option<EncodedTerm>,
+        graph_name: Option<EncodedTerm>,
+    ) -> DecodingIndexIterator<'a> {
         match subject {
             Some(subject) => match predicate {
                 Some(predicate) => match object {
                     Some(object) => match graph_name {
-                        Some(graph_name) => {
-                            let quad = EncodedQuad::new(subject, predicate, object, graph_name);
-                            match handle.contains(&quad) {
-                                Ok(true) => Box::new(once(Ok(quad))),
-                                Ok(false) => Box::new(empty()),
-                                Err(error) => Box::new(once(Err(error))),
-                            }
-                        }
-                        None => Box::new(
-                            handle.quads_for_subject_predicate_object(subject, predicate, object),
-                        ),
+                        Some(graph_name) => self
+                            .spog_quads(encode_term_quad(subject, predicate, object, graph_name)),
+                        None => self.quads_for_subject_predicate_object(subject, predicate, object),
                     },
                     None => match graph_name {
-                        Some(graph_name) => Box::new(
-                            handle
-                                .quads_for_subject_predicate_graph(subject, predicate, graph_name),
-                        ),
-                        None => Box::new(handle.quads_for_subject_predicate(subject, predicate)),
+                        Some(graph_name) => {
+                            self.quads_for_subject_predicate_graph(subject, predicate, graph_name)
+                        }
+                        None => self.quads_for_subject_predicate(subject, predicate),
                     },
                 },
                 None => match object {
                     Some(object) => match graph_name {
-                        Some(graph_name) => Box::new(
-                            handle.quads_for_subject_object_graph(subject, object, graph_name),
-                        ),
-                        None => Box::new(handle.quads_for_subject_object(subject, object)),
-                    },
-                    None => match graph_name {
                         Some(graph_name) => {
-                            Box::new(handle.quads_for_subject_graph(subject, graph_name))
+                            self.quads_for_subject_object_graph(subject, object, graph_name)
                         }
-                        None => Box::new(handle.quads_for_subject(subject)),
+                        None => self.quads_for_subject_object(subject, object),
+                    },
+                    None => match graph_name {
+                        Some(graph_name) => self.quads_for_subject_graph(subject, graph_name),
+                        None => self.quads_for_subject(subject),
                     },
                 },
             },
             None => match predicate {
                 Some(predicate) => match object {
                     Some(object) => match graph_name {
-                        Some(graph_name) => Box::new(
-                            handle.quads_for_predicate_object_graph(predicate, object, graph_name),
-                        ),
-                        None => Box::new(handle.quads_for_predicate_object(predicate, object)),
-                    },
-                    None => match graph_name {
                         Some(graph_name) => {
-                            Box::new(handle.quads_for_predicate_graph(predicate, graph_name))
+                            self.quads_for_predicate_object_graph(predicate, object, graph_name)
                         }
-                        None => Box::new(handle.quads_for_predicate(predicate)),
+
+                        None => self.quads_for_predicate_object(predicate, object),
+                    },
+                    None => match graph_name {
+                        Some(graph_name) => self.quads_for_predicate_graph(predicate, graph_name),
+                        None => self.quads_for_predicate(predicate),
                     },
                 },
                 None => match object {
                     Some(object) => match graph_name {
-                        Some(graph_name) => {
-                            Box::new(handle.quads_for_object_graph(object, graph_name))
-                        }
-                        None => Box::new(handle.quads_for_object(object)),
+                        Some(graph_name) => self.quads_for_object_graph(object, graph_name),
+                        None => self.quads_for_object(object),
                     },
                     None => match graph_name {
-                        Some(graph_name) => Box::new(handle.quads_for_graph(graph_name)),
-                        None => Box::new(handle.quads()),
+                        Some(graph_name) => self.quads_for_graph(graph_name),
+                        None => self.quads(),
                     },
                 },
             },
         }
     }
-}
 
-impl<'a> RocksDbStoreHandle<'a> {
-    fn transaction(&self) -> RocksDbTransaction<'a> {
-        RocksDbTransaction {
-            inner: RocksDbInnerTransaction {
-                handle: self.clone(),
-                batch: WriteBatch::default(),
-                buffer: Vec::default(),
-            },
-        }
-    }
-
-    fn auto_transaction(&self) -> RocksDbAutoTransaction<'a> {
-        RocksDbAutoTransaction {
-            inner: RocksDbInnerTransaction {
-                handle: self.clone(),
-                batch: WriteBatch::default(),
-                buffer: Vec::default(),
-            },
-        }
-    }
-
-    fn contains(&self, quad: &EncodedQuad) -> Result<bool> {
-        let mut buffer = Vec::with_capacity(4 * WRITTEN_TERM_MAX_SIZE);
-        write_spog_quad(&mut buffer, quad);
-        Ok(self.db.get_pinned_cf(self.spog_cf, &buffer)?.is_some())
-    }
-
-    fn quads(&self) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    fn quads(&self) -> DecodingIndexIterator<'a> {
         self.spog_quads(Vec::default())
     }
 
-    fn quads_for_subject(
-        &self,
-        subject: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    fn quads_for_subject(&self, subject: EncodedTerm) -> DecodingIndexIterator<'a> {
         self.spog_quads(encode_term(subject))
     }
 
@@ -363,7 +353,7 @@ impl<'a> RocksDbStoreHandle<'a> {
         &self,
         subject: EncodedTerm,
         predicate: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    ) -> DecodingIndexIterator<'a> {
         self.spog_quads(encode_term_pair(subject, predicate))
     }
 
@@ -372,7 +362,7 @@ impl<'a> RocksDbStoreHandle<'a> {
         subject: EncodedTerm,
         predicate: EncodedTerm,
         object: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    ) -> DecodingIndexIterator<'a> {
         self.spog_quads(encode_term_triple(subject, predicate, object))
     }
 
@@ -380,14 +370,11 @@ impl<'a> RocksDbStoreHandle<'a> {
         &self,
         subject: EncodedTerm,
         object: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    ) -> DecodingIndexIterator<'a> {
         self.ospg_quads(encode_term_pair(object, subject))
     }
 
-    fn quads_for_predicate(
-        &self,
-        predicate: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    fn quads_for_predicate(&self, predicate: EncodedTerm) -> DecodingIndexIterator<'a> {
         self.posg_quads(encode_term(predicate))
     }
 
@@ -395,21 +382,15 @@ impl<'a> RocksDbStoreHandle<'a> {
         &self,
         predicate: EncodedTerm,
         object: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    ) -> DecodingIndexIterator<'a> {
         self.posg_quads(encode_term_pair(predicate, object))
     }
 
-    fn quads_for_object(
-        &self,
-        object: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    fn quads_for_object(&self, object: EncodedTerm) -> DecodingIndexIterator<'a> {
         self.ospg_quads(encode_term(object))
     }
 
-    fn quads_for_graph(
-        &self,
-        graph_name: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    fn quads_for_graph(&self, graph_name: EncodedTerm) -> DecodingIndexIterator<'a> {
         self.gspo_quads(encode_term(graph_name))
     }
 
@@ -417,7 +398,7 @@ impl<'a> RocksDbStoreHandle<'a> {
         &self,
         subject: EncodedTerm,
         graph_name: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    ) -> DecodingIndexIterator<'a> {
         self.gspo_quads(encode_term_pair(graph_name, subject))
     }
 
@@ -426,7 +407,7 @@ impl<'a> RocksDbStoreHandle<'a> {
         subject: EncodedTerm,
         predicate: EncodedTerm,
         graph_name: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    ) -> DecodingIndexIterator<'a> {
         self.gspo_quads(encode_term_triple(graph_name, subject, predicate))
     }
 
@@ -435,7 +416,7 @@ impl<'a> RocksDbStoreHandle<'a> {
         subject: EncodedTerm,
         object: EncodedTerm,
         graph_name: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    ) -> DecodingIndexIterator<'a> {
         self.gosp_quads(encode_term_triple(graph_name, object, subject))
     }
 
@@ -443,7 +424,7 @@ impl<'a> RocksDbStoreHandle<'a> {
         &self,
         predicate: EncodedTerm,
         graph_name: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    ) -> DecodingIndexIterator<'a> {
         self.gpos_quads(encode_term_pair(graph_name, predicate))
     }
 
@@ -452,7 +433,7 @@ impl<'a> RocksDbStoreHandle<'a> {
         predicate: EncodedTerm,
         object: EncodedTerm,
         graph_name: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    ) -> DecodingIndexIterator<'a> {
         self.gpos_quads(encode_term_triple(graph_name, predicate, object))
     }
 
@@ -460,58 +441,46 @@ impl<'a> RocksDbStoreHandle<'a> {
         &self,
         object: EncodedTerm,
         graph_name: EncodedTerm,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+    ) -> DecodingIndexIterator<'a> {
         self.gosp_quads(encode_term_pair(graph_name, object))
     }
 
-    fn spog_quads(&self, prefix: Vec<u8>) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
-        self.inner_quads(self.spog_cf, prefix, |buffer| {
-            Cursor::new(buffer).read_spog_quad()
-        })
+    fn spog_quads(&self, prefix: Vec<u8>) -> DecodingIndexIterator<'a> {
+        self.inner_quads(self.spog_cf, prefix, QuadEncoding::SPOG)
     }
 
-    fn posg_quads(&self, prefix: Vec<u8>) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
-        self.inner_quads(self.posg_cf, prefix, |buffer| {
-            Cursor::new(buffer).read_posg_quad()
-        })
+    fn posg_quads(&self, prefix: Vec<u8>) -> DecodingIndexIterator<'a> {
+        self.inner_quads(self.posg_cf, prefix, QuadEncoding::POSG)
     }
 
-    fn ospg_quads(&self, prefix: Vec<u8>) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
-        self.inner_quads(self.ospg_cf, prefix, |buffer| {
-            Cursor::new(buffer).read_ospg_quad()
-        })
+    fn ospg_quads(&self, prefix: Vec<u8>) -> DecodingIndexIterator<'a> {
+        self.inner_quads(self.ospg_cf, prefix, QuadEncoding::OSPG)
     }
 
-    fn gspo_quads(&self, prefix: Vec<u8>) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
-        self.inner_quads(self.gspo_cf, prefix, |buffer| {
-            Cursor::new(buffer).read_gspo_quad()
-        })
+    fn gspo_quads(&self, prefix: Vec<u8>) -> DecodingIndexIterator<'a> {
+        self.inner_quads(self.gspo_cf, prefix, QuadEncoding::GSPO)
     }
 
-    fn gpos_quads(&self, prefix: Vec<u8>) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
-        self.inner_quads(self.gpos_cf, prefix, |buffer| {
-            Cursor::new(buffer).read_gpos_quad()
-        })
+    fn gpos_quads(&self, prefix: Vec<u8>) -> DecodingIndexIterator<'a> {
+        self.inner_quads(self.gpos_cf, prefix, QuadEncoding::GPOS)
     }
 
-    fn gosp_quads(&self, prefix: Vec<u8>) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
-        self.inner_quads(self.gosp_cf, prefix, |buffer| {
-            Cursor::new(buffer).read_gosp_quad()
-        })
+    fn gosp_quads(&self, prefix: Vec<u8>) -> DecodingIndexIterator<'a> {
+        self.inner_quads(self.gosp_cf, prefix, QuadEncoding::GOSP)
     }
 
     fn inner_quads(
         &self,
         cf: &ColumnFamily,
         prefix: Vec<u8>,
-        decode: impl Fn(&[u8]) -> Result<EncodedQuad> + 'a,
-    ) -> impl Iterator<Item = Result<EncodedQuad>> + 'a {
+        encoding: QuadEncoding,
+    ) -> DecodingIndexIterator<'a> {
         let mut iter = self.db.raw_iterator_cf(cf);
         iter.seek(&prefix);
         DecodingIndexIterator {
             iter,
             prefix,
-            decode,
+            encoding,
         }
     }
 }
@@ -699,9 +668,10 @@ impl RocksDbInnerTransaction<'_> {
     }
 }
 
-fn get_cf<'a>(db: &'a DB, name: &str) -> Result<&'a ColumnFamily> {
+#[allow(clippy::option_expect_used)]
+fn get_cf<'a>(db: &'a DB, name: &str) -> &'a ColumnFamily {
     db.cf_handle(name)
-        .ok_or_else(|| Error::msg(format!("column family {} not found", name)))
+        .expect("A column family that should exists in RocksDB does not exists")
 }
 
 fn encode_term(t: EncodedTerm) -> Vec<u8> {
@@ -725,19 +695,28 @@ fn encode_term_triple(t1: EncodedTerm, t2: EncodedTerm, t3: EncodedTerm) -> Vec<
     vec
 }
 
-struct DecodingIndexIterator<'a, F: Fn(&[u8]) -> Result<EncodedQuad>> {
+fn encode_term_quad(t1: EncodedTerm, t2: EncodedTerm, t3: EncodedTerm, t4: EncodedTerm) -> Vec<u8> {
+    let mut vec = Vec::with_capacity(4 * WRITTEN_TERM_MAX_SIZE);
+    write_term(&mut vec, t1);
+    write_term(&mut vec, t2);
+    write_term(&mut vec, t3);
+    write_term(&mut vec, t4);
+    vec
+}
+
+struct DecodingIndexIterator<'a> {
     iter: DBRawIterator<'a>,
     prefix: Vec<u8>,
-    decode: F,
+    encoding: QuadEncoding,
 }
 
-impl<'a, F: Fn(&[u8]) -> Result<EncodedQuad>> Iterator for DecodingIndexIterator<'a, F> {
+impl<'a> Iterator for DecodingIndexIterator<'a> {
     type Item = Result<EncodedQuad>;
 
     fn next(&mut self) -> Option<Result<EncodedQuad>> {
         if let Some(key) = self.iter.key() {
             if key.starts_with(&self.prefix) {
-                let result = (self.decode)(key);
+                let result = self.encoding.decode(key);
                 self.iter.next();
                 Some(result)
             } else {