[Issue 20670] immutable template specialization pattern matches immutable struct, strips immutable

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20670

--- Comment #12 from Paul Backus <snarwin+bugzilla at gmail.com> ---
> Because, since you've already gained, necessarily, the ability to deal with types that cannot be turned into mutable declarations by any means, there is no point to stripping immutable from `immutable struct S` anymore. What does it buy you?

As Dennis said: fewer special cases in the type system.

Forget about Unqual. It was just meant to be an example (evidently not a very
good one). Avoiding special cases in the type system is the point.

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