On Thu, Nov 08, 2012 at 09:37:00PM -0800, H. S. Teoh wrote:
> On Thu, Nov 08, 2012 at 11:51:29PM -0500, Nick Sabalausky wrote:
[...]
> > Those are only half-solutions as they only prevent false-negatives,
> > not false-positives. Plus, there's nothing to prevent people from
> > forgetting to do it in the first place.
>
> IOW, you want the user-defined type to declare that it's an input
> range, and not just some random struct that happens to have input
> range like functions?
>
> What about modifying isInputRange to be something like this:
>
> template isInputRange(R) {
> static if (R.implementsInputRange &&
> /* ... check for input range properties here */)
> {
> enum isInputRange = true;
> } else {
> enum isInputRange = false;
> }
> }
>
> Then all input ranges will have to explicitly declare they are an
> input range thus:
>
> struct MyInpRange {
> // This asserts that we're trying to be an input range
> enum implementsInputRange = true;
>
> // ... define .empty, .front, .popFront here
> }
>
> Any prospective input range that doesn't define implementsInputRange
> will be rejected by all input range functions. (Of course, that's just
> a temporary name, you can probably think of a better one.)
>
> You can also make it a mixin, or something like that, if you want to
> avoid the tedium of defining an enum to be true every single time.
[...]
Here's a slight refinement:
// Note: untested code
mixin template imAnInputRange() {
static assert(isInputRange!(typeof(this)));
enum implementsInputRange = true;
}
struct MyInpRange {
// This should croak loudly if this struct isn't a valid
// input range. Omitting this line makes range functions
// reject it too (provided we modify isInputRange as
// described above).
mixin imAnInputRange;
// implement range functions here
}
T
--
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