Rust-PHF

Documentation

Rust-PHF is a library to generate efficient lookup tables at compile time using perfect hash functions.

It currently uses the CHD algorithm and can generate a 100,000 entry map in roughly .4 seconds. By default statistics are not produced, but if you set the environment variable PHF_STATS it will issue a compiler note about how long it took.

MSRV (minimum supported rust version) is Rust 1.41, or 1.46 if you use the uncased feature.

Usage

PHF data structures can be constucted via either the procedural macros in the phf_macros crate or code generation supported by the phf_codegen crate.

To compile the phf crate with a dependency on libcore instead of libstd, enabling use in environments where libstd will not work, set default-features = false for the dependency:

[dependencies]
# to use `phf` in `no_std` environments
phf = { version = "0.9", default-features = false }

phf_macros

use phf::phf_map;

#[derive(Clone)]
pub enum Keyword {
    Loop,
    Continue,
    Break,
    Fn,
    Extern,
}

static KEYWORDS: phf::Map<&'static str, Keyword> = phf_map! {
    "loop" => Keyword::Loop,
    "continue" => Keyword::Continue,
    "break" => Keyword::Break,
    "fn" => Keyword::Fn,
    "extern" => Keyword::Extern,
};

pub fn parse_keyword(keyword: &str) -> Option<Keyword> {
    KEYWORDS.get(keyword).cloned()
}

[dependencies]
phf = { version = "0.9", features = ["macros"] }

Note

Currently, the macro syntax has some limitations and may not work as you want. See #183 or #196 for example.

phf_codegen

build.rs:

use std::env;
use std::fs::File;
use std::io::{BufWriter, Write};
use std::path::Path;

fn main() {
    let path = Path::new(&env::var("OUT_DIR").unwrap()).join("codegen.rs");
    let mut file = BufWriter::new(File::create(&path).unwrap());

    write!(&mut file, "static KEYWORDS: phf::Map<&'static str, Keyword> = ").unwrap();
    phf_codegen::Map::new()
        .entry("loop", "Keyword::Loop")
        .entry("continue", "Keyword::Continue")
        .entry("break", "Keyword::Break")
        .entry("fn", "Keyword::Fn")
        .entry("extern", "Keyword::Extern")
        .build(&mut file)
        .unwrap();
    write!(&mut file, ";\n").unwrap();
}

lib.rs:

#[derive(Clone)]
enum Keyword {
    Loop,
    Continue,
    Break,
    Fn,
    Extern,
}

include!(concat!(env!("OUT_DIR"), "/codegen.rs"));

pub fn parse_keyword(keyword: &str) -> Option<Keyword> {
    KEYWORDS.get(keyword).cloned()
}