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 1.46.
PHF data structures can be constructed 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 = "0.10", default-features = false }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 = "0.10", features = ["macros"] }Currently, the macro syntax has some limitations and may not work as you want. See #183 or #196 for example.
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> = {}",
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()
)
.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()
}