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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((ref x) => x(lvalueOf!R.front))) && (!isBidirectionalRange!R || is(typeof((ref x) => x(lvalueOf!R.back)))) && (!isRandomAccessRange!R || is(typeof((ref x) => x(lvalueOf!R[0]))));

void passByRef(ref ElementType!R stuff);
...
static assert(isInputRange!R);
passByRef(r.front);
static if (isBidirectionalRange!R) passByRef(r.back);
static if (isRandomAccessRange!R) passByRef(r[0]);

Example

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)));

Authors

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

License

Boost License 1.0.