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// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// An "interner" is a data structure that associates values with uint tags and
// allows bidirectional lookup; i.e. given a value, one can easily find the
// type, and vice versa.
// allow the interner_key macro to escape this module:
#[macro_escape];
use core::cmp::Equiv;
use core::hashmap::HashMap;
pub struct Interner<T> {
priv map: @mut HashMap<T, uint>,
priv vect: @mut ~[T],
}
// when traits can extend traits, we should extend index<uint,T> to get []
pub impl<T:Eq + IterBytes + Hash + Const + Copy> Interner<T> {
fn new() -> Interner<T> {
Interner {
map: @mut HashMap::new(),
vect: @mut ~[],
}
}
fn prefill(init: &[T]) -> Interner<T> {
let rv = Interner::new();
for init.each() |v| { rv.intern(*v); }
rv
}
fn intern(&self, val: T) -> uint {
match self.map.find(&val) {
Some(&idx) => return idx,
None => (),
}
let vect = &*self.vect;
let new_idx = vect.len();
self.map.insert(val, new_idx);
self.vect.push(val);
new_idx
}
fn gensym(&self, val: T) -> uint {
let new_idx = {
let vect = &*self.vect;
vect.len()
};
// leave out of .map to avoid colliding
self.vect.push(val);
new_idx
}
// this isn't "pure" in the traditional sense, because it can go from
// failing to returning a value as items are interned. But for typestate,
// where we first check a pred and then rely on it, ceasing to fail is ok.
fn get(&self, idx: uint) -> T { self.vect[idx] }
fn len(&self) -> uint { let vect = &*self.vect; vect.len() }
fn find_equiv<Q:Hash + IterBytes + Equiv<T>>(&self, val: &Q)
-> Option<uint> {
match self.map.find_equiv(val) {
Some(v) => Some(*v),
None => None,
}
}
}
/* Key for thread-local data for sneaking interner information to the
* encoder/decoder. It sounds like a hack because it is one.
* Bonus ultra-hack: functions as keys don't work across crates,
* so we have to use a unique number. See taskgroup_key! in task.rs
* for another case of this. */
macro_rules! interner_key (
() => (cast::transmute::<(uint, uint),
&fn(+v: @@::parse::token::ident_interner)>(
(-3 as uint, 0u)))
)
#[cfg(test)]
mod tests {
use super::*;
#[test]
#[should_fail]
fn i1 () {
let i : Interner<@~str> = Interner::new();
i.get(13);
}
#[test]
fn i2 () {
let i : Interner<@~str> = Interner::new();
// first one is zero:
assert_eq!(i.intern (@~"dog"), 0);
// re-use gets the same entry:
assert_eq!(i.intern (@~"dog"), 0);
// different string gets a different #:
assert_eq!(i.intern (@~"cat"), 1);
assert_eq!(i.intern (@~"cat"), 1);
// dog is still at zero
assert_eq!(i.intern (@~"dog"), 0);
// gensym gets 3
assert_eq!(i.gensym (@~"zebra" ), 2);
// gensym of same string gets new number :
assert_eq!(i.gensym (@~"zebra" ), 3);
// gensym of *existing* string gets new number:
assert_eq!(i.gensym (@~"dog"), 4);
assert_eq!(i.get(0), @~"dog");
assert_eq!(i.get(1), @~"cat");
assert_eq!(i.get(2), @~"zebra");
assert_eq!(i.get(3), @~"zebra");
assert_eq!(i.get(4), @~"dog");
}
#[test]
fn i3 () {
let i : Interner<@~str> = Interner::prefill([@~"Alan",@~"Bob",@~"Carol"]);
assert_eq!(i.get(0), @~"Alan");
assert_eq!(i.get(1), @~"Bob");
assert_eq!(i.get(2), @~"Carol");
assert_eq!(i.intern(@~"Bob"), 1);
}
}
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