On Tuesday, 11 September 2012 at 19:07:52 UTC, Simen Kjaeraas wrote:
> On Tue, 11 Sep 2012 20:57:07 +0200, Maxim Fomin <maxim@maxim-fomin.ru> wrote:
>
>> I think it is UB rather than a bug. The spec says that return types must match exactly. AFAIK auto is a feature to infer return type, not to magically adjust to multiple incompatible types.
>
> I'd be surprised if this were not a bug. My expectation would be that the
> types be combined as with the ?: operator, just like std.traits.CommonType.
>
> If this is not a bug, it's certainly worth filing as an enhancement request.

It can do, but in compile time. At runtime it cannot know what type is returned (I suppose, but I am not expert in such things). Variant works because it does it in compile time, but buggy examples published so far do it at runtime.

With multiple alias this this should work.

int getInt() const { return this.ivalue; }
alias getInt this;
float getFloat() const { return this.fvalue; }
alias getFloat this;

Or with a class method for implicit conversion.

On 09/11/2012 08:57 PM, Maxim Fomin wrote:
>
> I think it is UB rather than a bug.

No, this is a bug.

> The spec says that return types must match exactly.

Exactly. If it was UB, the spec would say the behaviour is undefined if they don't match exactly.


> AFAIK auto is a feature to infer return type, not to
> magically adjust to multiple incompatible types.
>

On Tuesday, 11 September 2012 at 19:27:40 UTC, Timon Gehr wrote:
> On 09/11/2012 08:57 PM, Maxim Fomin wrote:
>>
>> I think it is UB rather than a bug.
>
> No, this is a bug.
>
>> The spec says that return types must match exactly.
>
> Exactly. If it was UB, the spec would say the behaviour is undefined if they don't match exactly.
>
>
>> AFAIK auto is a feature to infer return type, not to
>> magically adjust to multiple incompatible types.

So what? Should my code work or not?

On 09/11/2012 09:29 PM, Namespace wrote:
> On Tuesday, 11 September 2012 at 19:27:40 UTC, Timon Gehr wrote:
>> On 09/11/2012 08:57 PM, Maxim Fomin wrote:
>>>
>>> I think it is UB rather than a bug.
>>
>> No, this is a bug.
>>
>>> The spec says that return types must match exactly.
>>
>> Exactly. If it was UB, the spec would say the behaviour is undefined
>> if they don't match exactly.
>>
>>
>>> AFAIK auto is a feature to infer return type, not to
>>> magically adjust to multiple incompatible types.
>
> So what? Should my code work or not?

According to the spec it should fail compilation.

Ah ok. That's sad.

On Tuesday, 11 September 2012 at 19:35:58 UTC, Timon Gehr wrote:
> According to the spec it should fail compilation.

After rethinking it I agree that bug is in faulty compilation (assuming spec is correct), not in returning zero at runtime, which was thought previously.

My final implementation:
http://dpaste.dzfl.pl/4d2a045a

Any suggestions?

Namespace:

> I have this code, but it works not as expected:
> http://dpaste.dzfl.pl/6ce5b4dd

I suggest to file a bug:


auto foo(bool b) {
    final switch (b) {
        case true:
            return 10;
        case false:
            return 20.0;
    }
}
void main() {
    import std.stdio: writeln;
    writeln(foo(true));
    writeln(foo(false));
}


The acceptable results are a compile-time error for type mismatch, or a conversion of both literals to double. Probably the second is better. But a silent bit-level cast is not acceptable.

Bye,
bearophile

On Tuesday, 11 September 2012 at 21:13:02 UTC, bearophile wrote:
> Namespace:
>
>> I have this code, but it works not as expected:
>> http://dpaste.dzfl.pl/6ce5b4dd
>
> I suggest to file a bug:
>
>
> auto foo(bool b) {
>     final switch (b) {
>         case true:
>             return 10;
>         case false:
>             return 20.0;
>     }
> }
> void main() {
>     import std.stdio: writeln;
>     writeln(foo(true));
>     writeln(foo(false));
> }
>
>
> The acceptable results are a compile-time error for type mismatch, or a conversion of both literals to double. Probably the second is better. But a silent bit-level cast is not acceptable.
>
> Bye,
> bearophile

Sure that is the first i will do tomorrow.
But so far no suggestions?