Discussion Thread: DIP 1039--Static Arrays with Inferred Length--Community Review Round 1

jmh530 john.michael.hall at gmail.com
Wed Jan 6 19:04:14 UTC 2021


On Wednesday, 6 January 2021 at 18:34:31 UTC, Nick Treleaven 
wrote:
> On Wednesday, 6 January 2021 at 18:29:05 UTC, Nick Treleaven 
> wrote:
>> Can be fixed (probably with another name):
>>
>> //import std.array;
>
> Actually template overloading seems to work fine:
>
> template staticArray(T) {
>     T[n] staticArray(ulong n) (auto ref T[n] a) {return a;}
> }
>
> T[n] staticArray(T, ulong n) (auto ref T[n] a) {return a;}
>
> void main(){
>     auto a = [1,2,3].staticArray!float;
>     pragma(msg, typeof(a)); // float[3]
>     a.writeln();
>     [1,2,3].staticArray.writeln();
> }

What about something like below to handle any user-defined type.

import std.stdio: writeln;

template staticArray(T) {
     T[n] staticArray(ulong n) (auto ref T[n] a) {return a;}

     T[n] staticArray(U, ulong n) (auto ref U[n] a)
         if (!is(T == U))
     {
         T[n] output;
         for(size_t i = 0; i < n; i++) {
             output[i] = cast(T) a[i];
         }
         return output;
     }
}

T[n] staticArray(T, ulong n) (auto ref T[n] a) {return a;}

struct Foo {
     float x;
     T opCast(T)() {
         return cast(T) x;
     }
}

void main(){
     auto a = [1,2,3].staticArray!float;
     pragma(msg, typeof(a)); // float[3]
     a.writeln();
     [1,2,3].staticArray.writeln();

     auto b = [1,2,3].staticArray!Foo;
     b.writeln();
}



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