Request: Auto string mixin templates

[nazriel]

On Monday, 29 July 2013 at 10:54:37 UTC, JS wrote:
>
> I have a template t that returns a string that is always to be 
> used as a mixin.
>
> It is quite annoying to have to use mixin() on the template.
>
> e.g.,
>
> mixin(t!());
>
> It would be nice to be able to specify that the template is 
> mixed in at the call site.
>
> e.g.,
>
> string mixin template t() { ... }
>
>
> then
>
> t!(); // is equivalent to mixin(t!()); and no scope issues
>
> The post at
>
> http://forum.dlang.org/thread/wqmngajgejxreyzftrdw@forum.dlang.org#post-wqmngajgejxreyzftrdw:40forum.dlang.org
>
> Has an example case where I have to call mixin(tJoin!(...)) to 
> generate the code to join the strings. This statement can't be 
> wrapped in way to simplify it without defeating the purpose of 
> the optimization it gives.
>
> The problem is that when you use variables in a string mixin 
> that are outside the template definition and try to string 
> mixin(to hide the explicit mixin call), then those variables 
> are outside the scope making the call fail.
>
>
> In the code above, tJoin takes a variadic set of arguments and 
> forms a string that concatenates all of them(just as if you 
> typed it by hand) but also deals with string arrays by 
> inserting a call to a RT function that joins the array.
>
> so the output of tJoin is a code string that can be used to 
> concatenate all the arguments passed to it... e.g.,
>
> tJoin!(":", a, b, "c") ==> `a~b~"c"`; if a and b are strings.
>
> mixing in that string, e.g., mixin(tJoin!(":", a, b, "c")), 
> will concatenate a with b with c... but only if in the scope of 
> a and b. Hence, trying to wrap the mixin statement will change 
> it's scope and a and b will either be unknown or wrong.
>
> Having someway to specify that the template should 
> automatically be mixed in would help solve these sorts of 
> problems(I've ran across it before when trying to generate code 
> using a template and avoid the mixin statement).
>
> A few possible options are:
>
> string mixin template t() { ... }
>
> string template t() { ... }
>
> auto mixin template t() { ... }
>
> template t() { ... mixin enum t = ...; }
>
> template t() { ... mixin t = ...; }
>
> etc...


You already have mixin templates.

Eg:

http://dpaste.dzfl.pl/e4b2e17a

import core.stdc.stdio;

mixin template Test()
{
	class Meh
	{
		this()
		{
			printf("In Meh");
		}
	}
}

void main()
{	
     mixin Test;
	
     Meh m = new Meh();
}