implicitly convert function pointers to delegates

[Jarrett Billingsley]

On Sun, Oct 26, 2008 at 2:11 PM, KennyTM~ <kennytm at gmail.com> wrote:
> Moritz Warning wrote:
>>
>> Hi,
>>
>> some people discovered that functions can be wrapped into delegates
>> without allocation.
>>
>> Here is one out of several similar solutions:
>>
>> R delegate(T) toDg(R, T...)(R function(T) fp) {
>>    struct dg {
>>        R opCall(T t) {
>>            return (cast(R function(T)) this) (t);
>>        }
>>    }
>>    R delegate(T) t;
>>    t.ptr = fp;
>>    t.funcptr = &dg.opCall;
>>    return t;
>> }
>>
>> I would like to ask if we can get this into the language?
>> It would make working with delegates and function pointers much more
>> easier when function pointers implicitly convert to delegates when they
>> "have to".
>
> vote++ for implicit conversion. An FP can be *safely* converted to any DGs.
>
> BTW,
>
>  alias float delegate (in float) DG;
>
>  float area (in float radius) {
>        float r2 = radius * radius;
>        return 3.1415926535 * radius;
>  }
>
>  DG x;
>  x.ptr = null;
>  x.funcptr = &area;
>  // writefln(typeof(x.funcptr).stringof); // ensure it's an FP not DG.
>  writefln(x(10)); // writes 314.159 without any error.
>
>
> Why this simpler solution is not used? The function pointer can't touch the
> frame pointer anyway (an FP cannot access stuff outside its scope).
>

The calling conventions for functions and delegates is different.
This method does not work in the general case.