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Enum member std.range.primitives.hasLvalueElements

Tests whether the range R has lvalue elements. These are defined as elements that can be passed by reference and have their address taken. The following code should compile for any range with lvalue elements.

enum hasLvalueElements(R) = isInputRange!R && is(typeof(isLvalue(lvalueOf!R.front))) && (!isBidirectionalRange!R || is(typeof(isLvalue(lvalueOf!R.back)))) && (!isRandomAccessRange!R || is(typeof(isLvalue(lvalueOf!R[0]))));
void passByRef(ref ElementType!R stuff);
static assert(isInputRange!R);
static if (isBidirectionalRange!R) passByRef(r.back);
static if (isRandomAccessRange!R) passByRef(r[0]);


import std.range : iota, chain;

static assert( hasLvalueElements!(int[]));
static assert( hasLvalueElements!(const(int)[]));
static assert( hasLvalueElements!(inout(int)[]));
static assert( hasLvalueElements!(immutable(int)[]));
static assert(!hasLvalueElements!(typeof(iota(3))));

static assert(!hasLvalueElements!( string));
static assert( hasLvalueElements!(dstring));
static assert(!hasLvalueElements!( char[]));
static assert( hasLvalueElements!(dchar[]));

auto c = chain([1, 2, 3], [4, 5, 6]);
static assert( hasLvalueElements!(typeof(c)));


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.