Crate phf

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.

Usage

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. If you prefer macros, you can easily use them by enabling the macros feature of the phf crate, like:

 [dependencies]
 phf = { version = "0.10", features = ["macros"] }

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 }

Example (with the macros feature enabled)

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()
}

Alternatively, you can use the phf_codegen crate to generate PHF datatypes in a build script.

Note

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

Modules

• map
  An immutable map constructed at compile time.
• ordered_map
  An order-preserving immutable map constructed at compile time.
• ordered_set
  An order-preserving immutable set constructed at compile time.
• set
  An immutable set constructed at compile time.

Macros

• phf_map
  Macro to create a static (compile-time) Map.
• phf_ordered_map
  Macro to create a static (compile-time) OrderedMap.
• phf_ordered_set
  Macro to create a static (compile-time) OrderedSet.
• phf_set
  Macro to create a static (compile-time) Set.

Structs

• Map
  An immutable map constructed at compile time.
• OrderedMap
  An order-preserving immutable map constructed at compile time.
• OrderedSet
  An order-preserving immutable set constructed at compile time.
• Set
  An immutable set constructed at compile time.

Traits

• PhfHash
  A trait implemented by types which can be used in PHF data structures.