[Issue 14756] cannot deduce function with template constraint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14756

Kenji Hara  changed:

   What|Removed |Added

 CC||marco.le...@gmx.de

--- Comment #2 from Kenji Hara  ---
*** Issue 15042 has been marked as a duplicate of this issue. ***

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[Issue 14756] cannot deduce function with template constraint

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14756

Kenji Hara k.hara...@gmail.com changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 Resolution|--- |INVALID

--- Comment #1 from Kenji Hara k.hara...@gmail.com ---
(In reply to Tim from comment #0)

This behavior change is an intentional bug fix. See issue 14290.

 enum bool isInstanceOf(alias S, T) = is(T == S!Args, Args...);
 
 struct Test(size_t id)
 {
 static void from(Other)(Other other)
 if (isInstanceOf!(Test, Other))

In here, 'Test' represents an instantiated struct, not a template. By fixing
issue 14290, is-expression won't match to the instantiation form S!Args when S
is a struct.

 If the template constraint uses the is-expression directly, the error goes
 away.

When you rewrite the condition as follows:

static void from(Other)(Other other)
if (is(Other == Test!Args, Args...))

'Test' is still a struct, but in here, the is-expression can recognize it may
also represent the outer template Test(size_t id) because it's accessible
through the lexical scope.

To fix the issue, you need to pass explicitly the template 'Test' to the
isInstanceOf.

struct Test(size_t id)
{
static void from(Other)(Other other)
if (isInstanceOf!(.Test, Other))
// -- Use Module Scope Operator (http://dlang.org/module)
{}
}

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