• d-bugmail puremagic.com (53/53) Mar 24 2011 http://d.puremagic.com/issues/show_bug.cgi?id=5784

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=5784

           Summary: Template instantiation with enum constant as
                    parameter, missing implicit cast
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: pszturmaj tlen.pl


--- Comment #0 from Piotr Szturmaj <pszturmaj tlen.pl> 2011-03-24 22:42:41 PDT
---
When template is instantiated for the first time, using integral literal,
everything is ok. But if the same template is instantiated for the first time,
using enum constant as its parameter then instantiation can't be matched using
is expression.

struct A(int n)
{
    bool[n] nBooleans;
}

template isA(T)
{
    static if (is(T X == A!N, int N))
        enum isA = true;
    else
        enum isA = false;
}

enum int boolCount = 5;

Now, when first instantiation is using integer literal, it works ok:

alias A!5 fromLiteral;
alias A!boolCount fromEnum;

static assert(isA!(A!5)); // pass
static assert(isA!(A!boolCount)); // pass
static assert(is(A!5 == A!boolCount)); // pass

But, when first instantiation is using enum constant, the is expression fails:

alias A!boolCount fromEnum;
alias A!5 fromLiteral;

static assert(isA!(A!5)); // fail
static assert(isA!(A!boolCount)); // fail
static assert(is(A!5 == A!boolCount)); // pass

Note that only difference is order of alias declarations.

The cause of this bug is enum constant which is not implicitly casted to its
base type (int). With explicit casting everything is ok:

alias A!(cast(int)boolCount) fromEnum;
alias A!5 fromLiteral;

static assert(isA!(A!5)); // pass
static assert(isA!(A!boolCount)); // pass
static assert(is(A!5 == A!boolCount)); // pass

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