How to provide this arg or functor for algorithm?

[Ali Çehreli via Digitalmars-d-learn]

On 08/16/2015 03:36 PM, cym13 wrote:
> On Sunday, 16 August 2015 at 22:22:07 UTC, Ali Çehreli wrote:
>>
>> // HERE:
>> // Error: function deneme.func @nogc function allocates
>> //        a closure with the GC
>> @nogc auto func(uint[] arr, DelegateRef d)
>> {
>>     return arr.map!(a => d.d(a));
>> }
>
> Aren't you making another delegate in the map by using "=>" that needs
> to allocate because it uses 'd' which is out of its scope?

I did not see that at all. :) I've finally gotten it to work by stepping 
into template realm where the compiler is a master of attributes: :)

import std.stdio;
import std.range;
import std.algorithm;

struct Caller
{
     this(uint context) {
         _context = context;
     }

     // ADDED pure
     pure uint method(uint value) {
         return _context * value;
     }

     uint _context;
}

// Now the type of d is a template parameter
@nogc auto func(Func)(uint[] arr, Func d)
{
     return arr.map!(d);
}

void main(string[] args)
{
     uint[] arr = [1,2,3];
     uint context = 2;
     auto c = Caller(context);
     auto d = &c.method;

     writeln(func(arr, d));
}

Prints:

   [2, 4, 6]

Ali