Enum std.range.primitives.member isRandomAccessRange

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

• r.opIndex(n) returns a reference to the nth element in the range.

Although char[] and wchar[] (as well as their qualified versions including string and wstring) are arrays, isRandomAccessRange yields false for them because they use variable-length encodings (UTF-8 and UTF-16 respectively). These types are bidirectional ranges only.

Declaration

enum isRandomAccessRange(R) = is(typeof((inout int = 0)
{
static assert(isBidirectionalRange!R || isForwardRange!R && isInfinite!R);
R r = R.init;
auto e = r[1];
auto f = r.front;
static assert(is(typeof(e) == typeof(f)));
static assert(!isNarrowString!R);
static assert(hasLength!R || isInfinite!R);
static if (is(typeof(r[__dollar])))
{
static assert(is(typeof(f) == typeof(r[__dollar])));
static if (!isInfinite!R)
{
static assert(is(typeof(f) == typeof(r[__dollar - 1])));
}

}

}
));

Example

alias R = int[];

// range is finite and bidirectional or infinite and forward.
static assert(isBidirectionalRange!R ||
              isForwardRange!R && isInfinite!R);

R r = [0,1];
auto e = r[1]; // can index
auto f = r.front;
static assert(is(typeof(e) == typeof(f))); // same type for indexed and front
static assert(!isNarrowString!R); // narrow strings cannot be indexed as ranges
static assert(hasLength!R || isInfinite!R); // must have length or be infinite

// $ must work as it does with arrays if opIndex works with $
static if(is(typeof(r[$])))
{
    static assert(is(typeof(f) == typeof(r[$])));

    // $ - 1 doesn't make sense with infinite ranges but needs to work
    // with finite ones.
    static if(!isInfinite!R)
        static assert(is(typeof(f) == typeof(r[$ - 1])));
}