Multiple Template Specialization Types (in D1)?

Wed Jul 2 10:56:50 PDT 2008

"Jarrett Billingsley" <kb3ctd2 at yahoo.com> wrote in message 
news:g4g81l$n9b$1 at digitalmars.com...
> "Nick Sabalausky" <a at a.a> wrote in message
> news:g4g69h$j7v$1 at digitalmars.com...
>>
>> I can't decide if this is better of worse. Leaning towards worse ;)
>>
>> char[] Bar(char[] retType, char[] publicName, char[] privateName,
>>                char[] argsDecl, char[] argsCall, char[][] types)
>> {
>>    char[] ret;
>>    foreach(char[] type; types)
>>    {
>>        ret ~= "public "~retType~" 
>> "~publicName~"(T:"~type~")("~argsDecl~")
>> {"~privateName~"!(T)("~argsCall~");}";
>>    }
>>    return ret;
>> }
>>
>> mixin(Bar("void", "Foo", "Foo_dwc", "T arg", "arg", ["char", "wchar",
>> "dchar"]));
>>
>> void main(char[][] args)
>> {
>>    Foo('a');
>> }
>
> Now it's just getting silly.
>
> template MakeFunctions(RetType, char[] PublicName,
>    char[] PrivateName, Types...)
> {
>    static if(Types.length == 0)
>        const char[] MakeFunctions = "";
>    else
>        const char[] MakeFunctions =
>    "public " ~ RetType.stringof ~ " " ~ PublicName ~ "(T : " ~
>        Types[0].stringof ~ ")(T arg)\n"
>    "{\n"
>    "   return " ~ PrivateName ~ "(arg);\n"
>    "}\n"
>    ~ MakeFunctions!(RetType, PublicName, PrivateName, Types[1 .. $]);
> }
>
> public template NameOfFunc(alias f)
> {
>    // weirdness in dmdfe.
>    const char[] NameOfFunc = (&f).stringof[2 .. $];
> }
>
> private template BarImpl(char[] PublicName, alias PrivateFunc, Types...)
> {
>    alias typeof(&PrivateFunc!(Types[0])) FuncType;
>    alias ReturnTypeOf!(FuncType) RetType;
>
>    const ret = MakeFunctions!(RetType, PublicName,
>        NameOfFunc!(PrivateFunc!(Types[0])), Types);
> }
>
> public template Bar(char[] PublicName, alias PrivateFunc, Types...)
> {
>    static assert(Types.length > 0, "must have at least one type");
>    const Bar = BarImpl!(PublicName, PrivateFunc, Types).ret;
> }
>
> mixin(Bar!("Foo", Foo_dwc, char, wchar, dchar));
>
> Template-foo to the rescue, you can extract the return type directly from
> the alias to the private function.  :)
>
>

I turned that into a working compileable source file (attached, test5.d), 
and made notes of a few bits of weirdness that I noticed when getting it to 
compile.

I do actually like the end result though. Put it into a utility module, and 
it's a nicely DRY approach to the original problem that works around D1's 
lack of template constraints. (I'm a DRY junkie.)

I have a few other utility mixins I've been using. When I wrote them, I was 
having trouble getting template mixins to work without using the "CTFE that 
returns char[] and takes all-char[] paramaters" approach you saw in my 
original version of Bar. Studying that code above, I think I understand D's 
templates well enough now to maybe improve some of those other utility 
mixins I have. 

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`
end