Still exploring what D has to offer but this blew my mind:

import std.stdio;

struct Base
{
  void print(string text)
  {
    writeln("Base : " ~ text);
  }
  int add(int a, int b)
  {
    return a + b;
  }
}

struct Wrap
{
  auto opDispatch(string op, Args...)(Args args)
  {
    enum name = op;
    return __traits(getMember, base, name)(args);
  }
  Base base;
}

int main(string[] argv)
{
  Wrap wrap;
  wrap.print("wrapped call, magic!");
  auto res = wrap.add(1, 5);
  return 0;
}

I don't quite understand why "enum name" part is necessary (as my understanding is that "op" is compile-time constant anyway) but since I am crap at D that is what worked for me. I was thinking for log time how great something like that would be in C++ and I just tried this id D... Mind blown... std::reference_wrapper<> would be a zillion times more usable with equivalent of opDispatch() this powerful.

On Wednesday, 8 January 2014 at 23:20:06 UTC, Szymon Gatner wrote:
> I don't quite understand why "enum name" part is necessary

It isn't!

On Wednesday, 8 January 2014 at 23:20:06 UTC, Szymon Gatner wrote:
> Still exploring what D has to offer but this blew my mind:
>
> <snip>
>
> I don't quite understand why "enum name" part is necessary (as my understanding is that "op" is compile-time constant anyway) but since I am crap at D that is what worked for me. I was thinking for log time how great something like that would be in C++ and I just tried this id D... Mind blown... std::reference_wrapper<> would be a zillion times more usable with equivalent of opDispatch() this powerful.

There is also `alias this` for subtyping.

	import std.stdio;
	
	struct Base
	{
	  void print(string text)
	  {
		writeln("Base : " ~ text);
	  }
	  int add(int a, int b)
	  {
		return a + b;
	  }
	}
	
	struct Wrap
	{
	  Base base;
	  alias base this;
	}
	
	void baseOnly(Base b)
	{
		b.print("passed in a Wrap!");
	}
	
	int main(string[] argv)
	{
	  Wrap wrap;
	  wrap.print("wrapped call, magic!");
	  baseOnly(wrap);
	  auto res = wrap.add(1, 5);
	  return 0;
	}

Szymon Gatner:

Two small improvements in your code:

>     writeln("Base : " ~ text);

=>

     writeln("Base : ", text);


> int main(string[] argv)
> {
> ...
>   return 0;
> }

=>

> void main(string[] argv)
> {
> ...
> }

Or even:

> void main()
> {
> ...
> }

Bye,
bearophile

On Wednesday, 8 January 2014 at 23:26:26 UTC, Adam D. Ruppe wrote:
> On Wednesday, 8 January 2014 at 23:20:06 UTC, Szymon Gatner wrote:
>> I don't quite understand why "enum name" part is necessary
>
> It isn't!

Indeed, I don't know why it didn't compile for me the first time.

On Wednesday, 8 January 2014 at 23:27:37 UTC, Brad Anderson wrote:
> On Wednesday, 8 January 2014 at 23:20:06 UTC, Szymon Gatner wrote:
>> Still exploring what D has to offer but this blew my mind:
>>
>> <snip>
>>
>> I don't quite understand why "enum name" part is necessary (as my understanding is that "op" is compile-time constant anyway) but since I am crap at D that is what worked for me. I was thinking for log time how great something like that would be in C++ and I just tried this id D... Mind blown... std::reference_wrapper<> would be a zillion times more usable with equivalent of opDispatch() this powerful.
>
> There is also `alias this` for subtyping.
>
> 	import std.stdio;
> 	
> 	struct Base
> 	{
> 	  void print(string text)
> 	  {
> 		writeln("Base : " ~ text);
> 	  }
> 	  int add(int a, int b)
> 	  {
> 		return a + b;
> 	  }
> 	}
> 	
> 	struct Wrap
> 	{
> 	  Base base;
> 	  alias base this;
> 	}
> 	
> 	void baseOnly(Base b)
> 	{
> 		b.print("passed in a Wrap!");
> 	}
> 	
> 	int main(string[] argv)
> 	{
> 	  Wrap wrap;
> 	  wrap.print("wrapped call, magic!");
> 	  baseOnly(wrap);
> 	  auto res = wrap.add(1, 5);
> 	  return 0;
> 	}

I was actually thinking about subtyping too but I don't know how to do alias this with opDispatch() call forwarding to Base from Wrap

On Wednesday, 8 January 2014 at 23:46:28 UTC, bearophile wrote:
> Szymon Gatner:
>
> Two small improvements in your code:
>
>>    writeln("Base : " ~ text);
>
> =>
>
>      writeln("Base : ", text);
>
>
>> int main(string[] argv)
>> {
>> ...
>>  return 0;
>> }
>
> =>
>
>> void main(string[] argv)
>> {
>> ...
>> }
>
> Or even:
>
>> void main()
>> {
>> ...
>> }
>
> Bye,
> bearophile

Thanks, was not aware, main() was actually generated by VisualD

On Thursday, 9 January 2014 at 00:02:00 UTC, Szymon Gatner wrote:
> On Wednesday, 8 January 2014 at 23:46:28 UTC, bearophile wrote:
>> Or even:
>>
>>> void main()
>>> {
>>> ...
>>> }
>>
>> Bye,
>> bearophile
>
> Thanks, was not aware, main() was actually generated by VisualD

Yeah, VisualD was guilty of propagating that poor template for a long time. It's now fixed.

http://d.puremagic.com/issues/show_bug.cgi?id=11277