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Enum member std.range.primitives.isBidirectionalRange

Returns true if R is a bidirectional range. A bidirectional range is a forward range that also offers the primitives back and popBack. The following code should compile for any bidirectional range.

enum isBidirectionalRange(R) = isForwardRange!R && is(typeof((R r) => r.popBack)) && is(ReturnType!((R r) => r.back) == ElementType!R);

The semantics of a bidirectional range (not checkable during compilation) are assumed to be the following (r is an object of type R):

  • r.back returns (possibly a reference to) the last element in the range. Calling r.back is allowed only if calling r.empty has, or would have, returned false.

See Also

The header of std.range for tutorials on ranges.


alias R = int[];
R r = [0,1];
static assert(isForwardRange!R);           // is forward range
r.popBack();                               // can invoke popBack
auto t = r.back;                           // can get the back of the range
auto w = r.front;
static assert(is(typeof(t) == typeof(w))); // same type for front and back


Andrei Alexandrescu, David Simcha, and Jonathan M Davis. Credit for some of the ideas in building this module goes to Leonardo Maffi.


Boost License 1.0.