Would it be possible (and useful) to introduce declarations like `auto foo() if(isInputRange(auto));`
Is there anything preventing us from adding constraints on the
auto function return value? I mean, such language extension seems
to be quite useful.
For example, it would be no longer necessary to provide method
bodies for functions with auto return values.
In many cases this would eliminate the need for introducing an
interface.
interface returnsDuckTyped
{
auto foo() if(isInputRange(auto));
}
Re: Would it be possible (and useful) to introduce declarations like `auto foo() if(isInputRange(auto));`
On Thursday, 17 May 2012 at 11:49:18 UTC, Roman D. Boiko wrote:
Is there anything preventing us from adding constraints on the
auto function return value? I mean, such language extension
seems to be quite useful.
For example, it would be no longer necessary to provide method
bodies for functions with auto return values.
In many cases this would eliminate the need for introducing an
interface.
interface returnsDuckTyped
{
auto foo() if(isInputRange!auto);
}
(fixed typo)
Re: Would it be possible (and useful) to introduce declarations like `auto foo() if(isInputRange(auto));
`
To: digitalmars.D digitalmars-d@puremagic.com
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On Thursday, May 17, 2012 13:49:16 Roman D. Boiko wrote:
Is there anything preventing us from adding constraints on the
auto function return value? I mean, such language extension seems
to be quite useful.
For example, it would be no longer necessary to provide method
bodies for functions with auto return values.
In many cases this would eliminate the need for introducing an
interface.
interface returnsDuckTyped
{
auto foo() if(isInputRange(auto));
}
It would still be necessary, because the compiler needs to know what the
actual return type is. Knowing that the type implements popFront, front, and
empty isn't enough. It needs to know the actual, physical layout of the type
to generate the proper code. And when dealing with an interface, the return
type must be covariant, and unless the types are both classes and one is
derived from the other (directly or indirectly), they won't be covariant even
if they have all of the same functions.
- Jonathan M Davis
Re: Would it be possible (and useful) to introduce declarations like `auto foo() if(isInputRange(auto));
On Thursday, 17 May 2012 at 21:09:10 UTC, Jonathan M Davis wrote: It would still be necessary, because the compiler needs to know what the actual return type is. Knowing that the type implements popFront, front, and empty isn't enough. It needs to know the actual, physical layout of the type to generate the proper code. And when dealing with an interface, the return type must be covariant, and unless the types are both classes and one is derived from the other (directly or indirectly), they won't be covariant even if they have all of the same functions. - Jonathan M Davis I felt there is some fundamental problem, otherwise it would have been implemented already. But couldn't find any myself. Thanks!
Re: Would it be possible (and useful) to introduce declarations like `auto foo() if(isInputRange(auto)); `
On Thursday, May 17, 2012 13:49:16 Roman D. Boiko wrote:
Is there anything preventing us from adding constraints on the
auto function return value? I mean, such language extension seems
to be quite useful.
For example, it would be no longer necessary to provide method
bodies for functions with auto return values.
In many cases this would eliminate the need for introducing an
interface.
interface returnsDuckTyped
{
auto foo() if(isInputRange(auto));
}
It would still be necessary, because the compiler needs to know what the
actual return type is. Knowing that the type implements popFront, front, and
empty isn't enough. It needs to know the actual, physical layout of the type
to generate the proper code. And when dealing with an interface, the return
type must be covariant, and unless the types are both classes and one is
derived from the other (directly or indirectly), they won't be covariant even
if they have all of the same functions.
- Jonathan M Davis
