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.
PHF data structures can be constucted via either the compiler plugins in the
phf_macros crate or code generation supported by the phf_codegen crate.
Compiler plugins are not a stable part of Rust at the moment, so phf_macros
can only be used with nightlies.
The phf/core feature will compile the phf crate with a dependency on libcore instead of libstd, enabling use in environments where libstd will not work.
#![feature(proc_macro_hygiene)]
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 = "0.7", features = ["macros"] }build.rs
extern crate phf_codegen;
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
extern crate phf;
#[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()
}