Append to 'map' result

[Ali Çehreli via Digitalmars-d-learn]

On 07/04/2017 05:52 PM, Jean-Louis Leroy wrote:
> On Wednesday, 5 July 2017 at 00:28:01 UTC, Ali Çehreli wrote:
>> On 07/04/2017 04:57 PM, Jean-Louis Leroy wrote:
>>> [...]
>> No time to dig deeper but this is because the two ranges that chain()
>> receives do not have a common type. (Rather, that type is 'void'):
>>
>> [...]
>
> I suspect that that is the reason, although I checked in several ways
> that I had ClassInfo elements on both sides. Ok, I'll keep looking
> tomorrow with a fresh eye...

This is related to TypeInfo.init, which unfortunately is *not* the .init 
property in this case. :( Luckily, it will be fixed in 2.075. This is 
what object.d has:

class TypeInfo
{
// ...

     /**
      * Return default initializer.  If the type should be initialized 
to all
      * zeros, an array with a null ptr and a length equal to the type 
size will
      * be returned. For static arrays, this returns the default 
initializer for
      * a single element of the array, use `tsize` to get the correct size.
      */
     abstract const(void)[] initializer() nothrow pure const @safe @nogc;

     /// $(RED Removed.) Please use `initializer` instead.
     @disable static const(void)[] init(); // since 2.074
     /* Planned for 2.075: Remove init, making way for the init type 
property,
     fixing issue 12233. */
}

The problem is, ElementType relies on .init, which works on most other 
type but not TypeInfo:

template ElementType(R)
{
     static if (is(typeof(R.init.front.init) T))
         alias ElementType = T;
     else
         alias ElementType = void;
}

So, unfortunately, most Phobos range functions cannot be used with 
TypeInfo as they would invariably touch ElementType. Here is a halfway 
workaround that uses each() instead of map(): :/

import std.algorithm;

class C {
}

void main() {
     auto k = C.classinfo;

     TypeInfo_Class[] arr;

     each!(i => arr ~= i.classinfo)(k.interfaces);
     arr ~= k.base;
}

Ali