56 lines
1.8 KiB
Rust
56 lines
1.8 KiB
Rust
//! # Performance
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//!
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//! ## Runtime Performance
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//!
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//! See also the general Rust [Performance Book](https://nnethercote.github.io/perf-book/)
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//!
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//! Tips
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//! - Try `cargo add winnow -F simd`. For some it offers significant performance improvements
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//! - When enough cases of an [`alt`] have unique prefixes, prefer [`dispatch`]
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//! - When parsing text, try to parse as bytes (`u8`) rather than `char`s ([`BStr`] can make
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//! debugging easier)
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//! - Find simplified subsets of the grammar to parse, falling back to the full grammar when it
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//! doesn't work. For example, when parsing json strings, parse them without support for escapes,
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//! falling back to escape support if it fails.
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//! - Watch for large return types. A surprising place these can show up is when chaining parsers
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//! with a tuple.
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//!
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//! ## Build-time Performance
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//!
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//! Returning complex types as `impl Trait` can negatively impact build times. This can hit in
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//! surprising cases like:
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//! ```rust
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//! # use winnow::prelude::*;
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//! fn foo<I, O, E>() -> impl Parser<I, O, E>
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//! # where
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//! # I: winnow::stream::Stream<Token=O>,
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//! # I: winnow::stream::StreamIsPartial,
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//! # E: winnow::error::ParserError<I>,
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//! {
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//! // ...some chained combinators...
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//! # winnow::token::any
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//! }
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//! ```
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//!
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//! Instead, wrap the combinators in a closure to simplify the type:
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//! ```rust
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//! # use winnow::prelude::*;
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//! fn foo<I, O, E>() -> impl Parser<I, O, E>
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//! # where
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//! # I: winnow::stream::Stream<Token=O>,
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//! # I: winnow::stream::StreamIsPartial,
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//! # E: winnow::error::ParserError<I>,
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//! {
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//! move |input: &mut I| {
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//! // ...some chained combinators...
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//! # winnow::token::any
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//! .parse_next(input)
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//! }
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//! }
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//! ```
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#![allow(unused_imports)]
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use crate::combinator::alt;
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use crate::combinator::dispatch;
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use crate::stream::BStr;
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