O(1) dictionaries

[Jari-Matti Mäkelä]

mandel wrote:

> Tim Keating Wrote:
> 
>> mandel wrote:
>> > Hi,
>> > 
>> > I have made a dictionary that way:
>> > enum Word { Hello, Bye };
>> > char[][Word] dict;
>> > 
>> > static this()
>> > {
>> >    dict = [
>> >      Word.Hello : "Hello",
>> >      Word.Bye : "Bye"
>> >    ];
>> > }
>> > 
>> > Now there are two problems I have with this:
>> > 
>> > - the dict is an AA, but an array would be much faster,
>> >   but it is not possible to assign it via an array literal
>> >   with a mixed order and supplied keys.
>> > char[][Word.max] dict = [Word.Hello : "Hello", ...]
>> 
>> Why does the array literal have to be in mixed order? You can just do
>> the enum and the array in the same order:
>> 
>> enum Word { Hello, Bye };
>> char[] dict = [ "Hello", "Bye" ];
>> 
>> The only complication there is that for a dictionary of any meaningful
>> length, it won't line up quite as nicely. Ensuring each enum value
>> matches its correct word will be a real pain. In this situation, I might
>> use code generation.
> You named the reason, it won't line up.
> The dict may also change order when words are added and quite possibly
> regrouped. The entire alignment will be hard to maintain.

That's no good excuse to not use templates :P :

template _E(T...) {
  static if (T.length>1)
    const _E = T[0] ~ "," ~ _E!(T[1..$]);
  else
    const _E = T[0] ~ "};";
}

template _A(T...) {
  static if (T.length>1)
    const _A = `"` ~ T[0] ~ `"[],` ~ _A!(T[1..$]);
  else
    const _A = `"` ~ T[0] ~ `"[]];`;
}

template RealEnum(char[] aName, char[] eName, T...) {
  const RealEnum = "enum " ~ eName ~ "{" ~ _E!(T) ~
                   "char[][] " ~ aName ~ "=[" ~ _A!(T);
}

mixin(RealEnum!("Word", "dict", "Hello", "Bye"));

CTFE would produce smaller binaries though.