Re: 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