[Issue 21891] Cannot alias every kind that can be passed via variadic templates

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21891

--- Comment #3 from Andrei Alexandrescu <andrei at erdani.com> ---
(In reply to Paul Backus from comment #2)
> (In reply to Andrei Alexandrescu from comment #0)
> > So in fact 1 is bindable to an alias but somehow not in all contexts!
> 
> Specifically: an expression can bind to a template alias parameter, but is
> not allowed on the right-hand side of an alias declaration.
> 
> The reason `alias Y = X;` works but `alias Y = X[0];` doesn't is that `X` by
> itself on the right-hand side is parsed as a symbol, not an expression. The
> variadic parameter is a distraction.

Very interesting, thank you!

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