So I thought this might work:
struct MaybeEmpty(R) if (isInputRange!R) {
private bool _isEmpty;
private R _input;
alias _input this;
this(bool isEmpty, R input) {
_input = input;
_isEmpty = isEmpty;
}
@property bool empty() {
return _isEmpty || _input.empty;
}
}
auto maybeEmpty(R)(bool empty, R input = R.init) if
(isInputRange!R) {
return MaybeEmpty!R(empty, input);
}
It's kind of ugly, but it can be used like:
auto a = maybeEmpty!MyRange(true);
auto b = maybeEmpty!MyRange(false, actualRange);
static assert(is(typeof(a) == typeof(b)));
However, it fails the input range test:
static assert(isInputRange!MyRange); //pass
static assert(isInputRange!(typeof(a))); // fail
But it seems to be something weird with cross-module template
instantiation. If I replace `import std.range` with a copy-paste
of `isInputRange`, the above passes.
Either that or I'm doing something stupid because I'vebeen
staring at this too long.
I'm wondering if the isInputRange thing is a bug, so here's a
gist if anyone wants to play with it:
https://gist.github.com/rcorre/7a62395c53baf3c0bfbc
