Andrej Mitrovic wrote:
I'd love to see this used more in Phobos. I don't know if there are any
drawbacks, but this looks and works nicely:
import std.stdio : writeln;
void main()
{
writeln(isInputRange!(N));
}
class N
{
N test;
bool empty()
{
return false;
}
@property
void popFront()
{
}
@property
N front()
{
return test;
}
}
template isInputRange(R)
{
enum bool isInputRange = __traits(compiles,
{
R r; // can define a range object
if (r.empty) {} // can test for empty
r.popFront; // can invoke next
auto h = r.front; // can get the front of the range
});
}
If you uncomment some of those methods in class N, then you get back false,
which is what you want. Currently isInputRange is defined like so in Phobos:
template isInputRange(R)
{
enum bool isInputRange = is(typeof(
{
R r; // can define a range object
if (r.empty) {} // can test for empty
r.popFront; // can invoke next
auto h = r.front; // can get the front of the range
}()));
}
It's getting close to LISP! :)
If I remember correctly, it has been discussed not long ago that those
is(typeof(...))s should really be __traits(compiles). Maybe it's just
some code was written before those lovely __traits were introduced?..