On Friday, 31 July 2015 at 16:28:30 UTC, jmh530 wrote:
Looking at the PR also resolved my earlier question. Running
the code as below (do not import std.range) will tell you
exactly what isn't implemented from isInputRange (in this case,
I commented out popFront). Very cool.
template satisfies(alias Constraint, R) {
enum check = "check" ~ Constraint.stringof[2..$-3] ~ "!(R)";
enum assert_ = "static assert("~ check ~ ");";
mixin(assert_); //mixes in "static
assert(checkInputRange!R)"
}
template isInputRange(R)
{
enum bool isInputRange = is(typeof(checkInputRange!R));
}
bool checkInputRange(R)(inout int = 0)
{
if (__ctfe)
{
R r = R.init; // can define a range object
if (r.empty) {} // can test for empty
r.popFront(); // can invoke popFront()
auto h = r.front; // can get the front of the range
}
return true;
}
@satisfies!(isInputRange, Zeroes)
struct Zeroes {
enum empty = false;
//void popFront() {}
@property int front() { return 0; }
}
void main()
{
Zeroes Z;
}
Nice. Here are the actual error messages for the record:
/d125/f236.d(18): Error: no property 'popFront' for type 'Zeroes'
/d125/f236.d(24): Error: template instance
f236.satisfies!(isInputRange, Zeroes) error instantiating
Piotrek
