On Tue, 01 Mar 2011 18:11:00 -0500, bearophile <bearophileHUGS@lycos.com> wrote:

> http://d.puremagic.com/issues/show_bug.cgi?id=5678

I think there is a general bug where any time the compiler uses an enum, it simply replaces the expression declared for the enum.

So basically

enum TRUE = new DElement(true);

void main()
{
   auto delem1 = TRUE;
   auto delem2 = TRUE;
   assert(delem1 is delem2); // fails
}

gets morphed into this:

void main()
{
   auto delem1 = new Delement(true);
   auto delem2 = new Delement(true);
   assert(delem1 is delem2); // fails
}

Obviously this works great when the enum is a value type or a string literal (which is created at compile time).  However, it is not so great for things like AAs, array literals, objects, or structs.

I think there are a few of these bugs in bugzilla, and there should be at least a tracker, and if not, they should all be combined.  This is a serious problem in D, and really creates havoc (both performance-wise and semantically).  I don't anticipate there is an easy fix.

Essentially, I'd say enum is completely useless except for builtin types and strings.

-Steve

On 03/02/2011 02:24 PM, Steven Schveighoffer wrote:
> On Tue, 01 Mar 2011 18:11:00 -0500, bearophile <bearophileHUGS@lycos.com> wrote:
>
>> http://d.puremagic.com/issues/show_bug.cgi?id=5678
>
> I think there is a general bug where any time the compiler uses an enum, it
> simply replaces the expression declared for the enum.
>
> So basically
>
> enum TRUE = new DElement(true);
>
> void main()
> {
> auto delem1 = TRUE;
> auto delem2 = TRUE;
> assert(delem1 is delem2); // fails
> }
>
> gets morphed into this:
>
> void main()
> {
> auto delem1 = new Delement(true);
> auto delem2 = new Delement(true);
> assert(delem1 is delem2); // fails
> }
>
> Obviously this works great when the enum is a value type or a string literal
> (which is created at compile time). However, it is not so great for things like
> AAs, array literals, objects, or structs.
>
> I think there are a few of these bugs in bugzilla, and there should be at least
> a tracker, and if not, they should all be combined. This is a serious problem
> in D, and really creates havoc (both performance-wise and semantically). I
> don't anticipate there is an easy fix.
>
> Essentially, I'd say enum is completely useless except for builtin types and
> strings.

Thank you Steven & Bearophile. This solves my problem.
I first did not get Bearophile's answer about run/compile-time constants (I mean enums). I thought the time when they are created is irrelevant, isn't it?
Anyway, placing the constant defs inside a module's <static this () {...}> block does what I mean. It does, in fact, ensure *unicity*. But I don't really understand the relation with Steven's explanation above: why/how does the fact that a constant's def is inside static this() prevent the compiler to rewrite it like shown above? Also, I basically don't understand why dmd does that anyway: it's obviously un-ecological ;-)

Denis
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