https://issues.dlang.org/show_bug.cgi?id=21563
Issue ID: 21563
Summary: Make shadowing mixin template names an error
Product: D
Version: D2
Hardware: All
OS: All
Status: NEW
Severity: enhancement
Priority: P1
Component: dmd
Assignee: [email protected]
Reporter: [email protected]
If a mixin template only mixes in one name and that name is shadowed, this
should be an error. It is almost always unintended.
For mixin templates that declares multiple names, partial shadowing could be
the intended behavior, and as a corner case, full shadowing, too.
Meta-programming code would be complicated unnecessarily if it had to check
that not all members of a mixin template are shadowed. However, if the mixin
template contains one member (one name) only, shadowing is very likely to be
unintended.
Unless the mixin template name is a template parameter, the author of the mixin
statement has control over it.
Example code:
mixin template M()
{
void f() { }
}
struct S
{
int f(int x) { return x; }
mixin M; // does nothing
}
void main()
{
S s;
s.f(); // error
}
The improvement would be:
mixin template M()
{
void f() { }
}
struct S
{
int f(int x) { return x; }
mixin M; // error: only member `M().f` of `M()` shadowed.
}
The corrective action would be to give the mixin a name and alias the eponymous
member(s):
mixin template M()
{
void f() { }
}
struct S
{
int f(int x) { return x; }
mixin M m;
alias f = m.f;
}
--
