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54 lines
2.1 KiB
54 lines
2.1 KiB
# wee_alloc
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1. [What is `wee_alloc`?](#what-is-wee_alloc)
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2. [Enabling `wee_alloc`](#enabling-wee_alloc)
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3. [Rust nightly](#rust-nightly)
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## What is `wee_alloc`?
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Reducing the size of compiled WebAssembly code is important, since it is often transmitted over the Internet or placed on embedded devices.
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> `wee_alloc` is a tiny allocator designed for WebAssembly that has a (pre-compression) code-size footprint of only a single kilobyte.
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[An analysis](http://fitzgeraldnick.com/2018/02/09/wee-alloc.html) suggests that over half of the bare minimum WebAssembly memory footprint is required by Rust's default memory allocator. Yet, WebAssembly code often does not require a sophisticated allocator, since it often just requests a couple of large initial allocations.
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`wee_alloc` trades off size for speed. Although it has a tiny code-size footprint, it is relatively slow if additional allocations are needed.
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For even more details, see the [`wee_alloc` repository](https://github.com/rustwasm/wee_alloc).
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## Enabling `wee_alloc`
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In `lib.rs`, we have the configuration for `wee_alloc` inside a `cfg_if!` macro:
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```rust
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cfg_if! {
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if #[cfg(feature = "wee_alloc")] {
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extern crate wee_alloc;
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#[global_allocator]
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static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;
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}
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}
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```
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This code block is intended to initialize `wee_alloc` as the global memory allocator, but only if the `wee_alloc` feature is enabled in `Cargo.toml`.
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To do so we need to append `"wee_alloc"` to the `default` vector in `Cargo.toml`. Then, the `cfg_if!` block is replaced with the contents of the `if` block, shown above.
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```toml
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[features]
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default = ["console_error_panic_hook", "wee_alloc"]
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```
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## Rust nightly
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`wee_alloc` currently relies on features only available in Rust nightly. As such it requires you to use the nightly toolchain for compilation. If you have [Rustup](https://rustup.rs/) set up, you can install the nightly toolchain as follows:
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```
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rustup toolchain add nightly
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```
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To use `wasm-pack` with Rust nightly run:
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```
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rustup run nightly wasm-pack build
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```
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