Going from string to identifier

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On Wednesday, 21 February 2018 at 22:11:04 UTC, Jean-Louis Leroy 
wrote:
> Here's what I am trying to do:
>
> mixin template MakeFun(string ID, int X)
> {
>   int mixin(ID)() { return X; }
> }
>
> mixin MakeFun!("one", 1); // int one() { return 1; }
>
> Alas I get:
> makefunc.d(3): Error: no identifier for declarator `int`
> makefunc.d(3): Error: found `{` when expecting `;`
> makefunc.d(3): Error: declaration expected, not `return`
> makefunc.d(4): Error: unrecognized declaration
>
> Is there a shorter way than building the entire function 
> definition as a string mixin? As in:
>
> mixin template MakeFun(string ID, int X)
> {
>   import std.format;
>   mixin(format("int %s() { return %s; }", ID, X));
> }
>
> mixin MakeFun!("one", 1);

Mixins have to be full declarations. You can't mix in bits and 
pieces... except when you can:

import std.stdio;

void main()
{
     enum teste = "asdf";
     string s = mixin("teste");
     writeln(s); //Prints "asdf"
}

It looks like a grammar error as opposed to a semantic one. D's 
grammar just doesn't support `mixin` in the function name 
position. One way you can make it a little more palateable:

mixin template MakeFun(string ID, int X)
{
     import std.format;
     mixin(q{ int %s { return %s; } }.format(ID, X));
}

`q{}` denotes a token string that must contain valid tokens (I'm 
not sure if the available compiler implementations actually 
enforce this), and I _think_ token strings will be properly 
syntax-highlighted by most tools.

https://dlang.org/spec/lex.html#token_strings