My template tuple code does not compile

[Q. Schroll]

On Tuesday, 26 February 2019 at 21:43:31 UTC, Victor Porton wrote:
> Compilation of unittest at the bottom of this file fails with 
> an error. What is my error?

I cannot tell you, why exactly you get these error messages. I 
can explain you the probable cause of the errors. I have not 
tested anything of what I tell you, as it is very vague.

You have the line

    ProviderParams("S", ((int, "x"), (float, "y")));

Why do you even expect it to compile?
First, ProviderParams is a mixin template, so you'd need to 
instantiate it with the ! operator. Then, the expressions (int, 
"x") and so on do not make sense in D. You could have 
compile-time tuples (using AliasSeq from std.meta) containing 
types and other compile-time known stuff, but it wouldn't help 
directly.
You'd use the mixin template like this:

    mixin ProviderParams!("S", int, "x", float, "y");
    ^-- necessary       ^-- necessary

Grouping arguments could be done, but from my experience, it does 
not buy you anything; rather it makes it worse. Better just deal 
with heterogeneous stuff just like std.typecons.Tuple does.

You should definitely comment your code. Explain what you intend 
to do. It helps people helping you.