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October 23, 2013 Allow illegal code in enum initialization? | ||||
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Illegal code is accepted in static if, but not in enum declarations. This leads to having three lines when one is enough. Is this just an oversight, or by design? template T(alias A) { enum T = true; } void main() { struct S { } static if(__traits(compiles, S.a) && T!(S.a)) // ok enum e1 = true; else enum e1 = false; enum e2 = __traits(compiles, S.a) && T!(S.a); // No property S.a } |
October 23, 2013 Re: Allow illegal code in enum initialization? | ||||
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Posted in reply to simendsjo | On 10/23/2013 02:55 AM, simendsjo wrote:
> Illegal code is accepted in static if, but not in enum declarations.
> This leads to having three lines when one is enough. Is this just an
> oversight, or by design?
>
> template T(alias A) {
> enum T = true;
> }
>
> void main() {
> struct S { }
> static if(__traits(compiles, S.a) && T!(S.a)) // ok
> enum e1 = true;
> else
> enum e1 = false;
> enum e2 = __traits(compiles, S.a) && T!(S.a); // No property S.a
> }
I don't know whether it is even specified but it feels like a feature to me.
Just like the shortcut behavior of runtime if helps with avoiding illegal memory accesses, this helps with avoiding illegal code altogether:
// null access avoided
if ((p !is null) && (p.member == 42))
// illegal code avoided
static if (__traits(compiles, S.a) && (S.a == 42))
Ali
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October 23, 2013 Re: Allow illegal code in enum initialization? | ||||
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Posted in reply to Ali Çehreli | On Wednesday, 23 October 2013 at 16:27:47 UTC, Ali Çehreli wrote:
> On 10/23/2013 02:55 AM, simendsjo wrote:
>> Illegal code is accepted in static if, but not in enum declarations.
>> This leads to having three lines when one is enough. Is this just an
>> oversight, or by design?
>>
>> template T(alias A) {
>> enum T = true;
>> }
>>
>> void main() {
>> struct S { }
>> static if(__traits(compiles, S.a) && T!(S.a)) // ok
>> enum e1 = true;
>> else
>> enum e1 = false;
>> enum e2 = __traits(compiles, S.a) && T!(S.a); // No property S.a
>> }
>
> I don't know whether it is even specified but it feels like a feature to me.
>
> Just like the shortcut behavior of runtime if helps with avoiding illegal memory accesses, this helps with avoiding illegal code altogether:
>
> // null access avoided
> if ((p !is null) && (p.member == 42))
>
> // illegal code avoided
> static if (__traits(compiles, S.a) && (S.a == 42))
>
> Ali
The question is if it would make sense to allow it for enum as well as static if. As enum is a compile-time constant I think it would be consistent.
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