I have the following code:

private string getVariableSignalWrappersName(VarType)()
{
	return VarType.stringof ~ "SignalWrappers";
}

void addVariableListener(VarType)(int variableIndex, void delegate(int, VarType))
{
	alias typeSignalWrappers = mixin(getVariableSignalWrappersName!VarType);
}

On compilation, the following error is issued:
Error: basic type expected, not mixin

Why should it be like that? I believe the compiler should not impose restrictions on what mixins can or cannot do :/

On Friday, 10 June 2016 at 22:38:29 UTC, Dechcaudron wrote:
> I have the following code:
>
> private string getVariableSignalWrappersName(VarType)()
> {
> 	return VarType.stringof ~ "SignalWrappers";
> }
>
> void addVariableListener(VarType)(int variableIndex, void delegate(int, VarType))
> {
> 	alias typeSignalWrappers = mixin(getVariableSignalWrappersName!VarType);
> }
>
> On compilation, the following error is issued:
> Error: basic type expected, not mixin
>
> Why should it be like that? I believe the compiler should not impose restrictions on what mixins can or cannot do :/

I'm no expert, but this looks like a grammar issue more than anything else. You can work around it by moving the alias declaration into the mixin.

mixin("alias typeSignalWrappers = " ~ getVariableSignalWrappersName!VarType ~ ";");

On Friday, 10 June 2016 at 22:38:29 UTC, Dechcaudron wrote:
> Error: basic type expected, not mixin
>
> Why should it be like that? I believe the compiler should not impose restrictions on what mixins can or cannot do :/

This might be a gratuitous grammar restriction. There are a few of those surrounding alias "targets". A template that simply returns its parameter might work, though, such as std.meta.Alias (alias foo = Alias!(mixin(…));).

 — David

On Friday, 10 June 2016 at 22:38:29 UTC, Dechcaudron wrote:
> I have the following code:
>
> private string getVariableSignalWrappersName(VarType)()
> {
> 	return VarType.stringof ~ "SignalWrappers";
> }
>
> void addVariableListener(VarType)(int variableIndex, void delegate(int, VarType))
> {
> 	alias typeSignalWrappers = mixin(getVariableSignalWrappersName!VarType);
> }
>
> On compilation, the following error is issued:
> Error: basic type expected, not mixin
>
> Why should it be like that? I believe the compiler should not impose restrictions on what mixins can or cannot do :/

Mixins are statements. They cannot be a part of an expression.

The other two posts have demonstrated how to get around this.

On Saturday, 11 June 2016 at 02:33:46 UTC, Alex Parrill wrote:
> Mixins are statements.

No, they're not. Well, yes they are [1], but there are also mixin expressions [2]. Not to be confused with the TemplateMixin[3], which is indeed always a statement.

1: http://dlang.org/spec/grammar.html#MixinExpression
2: http://dlang.org/spec/grammar.html#MixinStatement
3: http://dlang.org/spec/grammar.html#TemplateMixin

On Saturday, 11 June 2016 at 02:46:00 UTC, Adam D. Ruppe wrote:
> On Saturday, 11 June 2016 at 02:33:46 UTC, Alex Parrill wrote:
>> Mixins are statements.
>
> No, they're not. Well, yes they are [1], but there are also mixin expressions [2]. Not to be confused with the TemplateMixin[3], which is indeed always a statement.
>
> 1: http://dlang.org/spec/grammar.html#MixinExpression
> 2: http://dlang.org/spec/grammar.html#MixinStatement
> 3: http://dlang.org/spec/grammar.html#TemplateMixin

Huh, every time I've used mixins, I've always run into the issue in the OP, so I assumed they were statements. It definitely seems like a bug then.

On Saturday, 11 June 2016 at 01:53:10 UTC, David Nadlinger wrote:
> This might be a gratuitous grammar restriction. There are a few of those surrounding alias "targets". A template that simply returns its parameter might work, though, such as std.meta.Alias (alias foo = Alias!(mixin(…));).

It seems to be that it would be a good idea to file this in as a suggested change/fix. Do I have support?