[Issue 8508] New: std.traits.isSomeString no longer works with enums
d-bugmail at puremagic.com
d-bugmail at puremagic.com
Sat Aug 4 14:20:32 PDT 2012
http://d.puremagic.com/issues/show_bug.cgi?id=8508
Summary: std.traits.isSomeString no longer works with enums
Product: D
Version: unspecified
Platform: All
OS/Version: All
Status: NEW
Severity: regression
Priority: P2
Component: Phobos
AssignedTo: nobody at puremagic.com
ReportedBy: jmdavisProg at gmx.com
--- Comment #0 from Jonathan M Davis <jmdavisProg at gmx.com> 2012-08-04 14:20:31 PDT ---
This code passes with 2.059 but fails with 2.060:
import std.traits;
enum E : string { a = "hello" }
static assert(isSomeString!(typeof(E.a)));
void main()
{
}
It's commit
https://github.com/D-Programming-Language/phobos/commit/52462bec6ea846f30e8dac309d63ccb4101e8f0c
which broke this. Kenji Hara argues that enums should be treated as strongly
typed by std.traits, but the language itself doesn't do this.
auto func(string s) {...}
will accept E.a just fine, but no
auto func(S)(S s) if(isSomeString!S) {...}
will not. Kenji also points out that std.traits has not been consistent with
regards to how it treats enums, and
enum U : uint { a = 0 }
static assert(isUnsigned!(typeof(U.a)));
fails with both 2.059 and 2.060. I'd argue that it should pass as well.
Needing to distinguish between an enum of a particular base type and that exact
type is quite rare AFAIK (std.conv.to and std.format care but not a lot else).
As such, I really think that we'd be better off if std.traits treats enums as
their base types and let code which cares about whether a particular template
argument is an enum or not check whether it's an enum - that's what is(T ==
enum) is for.
As it stands, it's _very_ easy to break code which uses enums when templatizing
a function which wasn't previously templatized, and std.traits is completely
inconsistent with the language with regards to enums. This needs to be fixed.
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