3 unstable releases
Uses old Rust 2015
0.2.0-beta | Jul 29, 2017 |
---|---|
0.1.1 | Jul 17, 2017 |
0.1.0 | Jul 16, 2017 |
#69 in #hashmap
220KB
170 lines
Static Map
A static round-robin hashmap implementation, using the same hasher found in rustc. This is currently written using a bang variant of procedural macros that is only avialable in nightly at the moment. Procedural macros are currently in active development, so I woulnd't expect any kind of stability here for the moment. This was just an exercise to gain experience for how procedural macro development may become.
Example
#[macro_use]
extern crate static_map;
#[macro_use]
extern crate static_map_macros;
use static_map::Map;
#[derive(Clone, Copy)]
struct RGB(u8, u8, u8);
static CSS_COLORS: Map<&'static str, RGB> = static_map! {
Default: RGB(0x00,0x00,0x00),
"black" => RGB(0x00,0x00,0x00),
"silver" => RGB(0xc0,0xc0,0xc0),
"gray" => RGB(0x80,0x80,0x80),
"white" => RGB(0xff,0xff,0xff),
"maroon" => RGB(0x80,0x00,0x00),
"red" => RGB(0xff,0x00,0x00),
"purple" => RGB(0x80,0x00,0x80),
"fuchsia" => RGB(0xff,0x00,0xff),
"green" => RGB(0x00,0x80,0x00),
};
pub fn rgb_from_str(color: &str) -> Option<RGB> {
CSS_COLORS.get(color).cloned()
}
Notice that Default: RGB(0, 0, 0),
. This is required since we are initializing an array which will contain empty slots.
We need a default value for those slots and you declare it as such. PHF maps do not require this since they are, well, perfect.
Also note that #[macro_use]
is required for both static_map
and static_map_macros
. This is because proc_macros
are not
allowed to export items, so the static_map!
macro lives in the static_map
crate. (Note: This is not entirely true, and may be fixed soon).
Benchmarks
The idea is that a static round-robin hashmap maybe more efficient than PHF for certain datasets. The trade-off is that a PHF hashmap
implementation is nearly optimal with respect to memory efficiency; static_map!
may use upto 2x as much memory in the worst case scenario.
Keep that in mind, here are some benchmarks (found in static_map_macro/benches
).
CSS Colors
This contains about 150 &str -> RGB(u8, u8, u8)
entries (like in the example above).
test bench_phf ... bench: 2,027 ns/iter (+/- 224)
test bench_static_map ... bench: 935 ns/iter (+/- 90)
Codepoints
This benchmark contains about 4500 u32 -> GlyphMetrics
entries.
test bench_phf ... bench: 44,502 ns/iter (+/- 3,971)
test bench_static_map ... bench: 13,097 ns/iter (+/- 2,768)
TeX Symbols
This benchmark contains about 1500 &str -> Symbol
entries, mapping tex symbols to codepoints.
test bench_phf ... bench: 20,382 ns/iter (+/- 133)
test bench_static_map ... bench: 24,589 ns/iter (+/- 188)
Dependencies
~2MB
~43K SLoC