The unary +
operator turns a lvalue into an rvalue:
struct A {
static const int value = 1;
};
// ...
int x = std::min(0, A::value);
Oh noes! This code won't link, because someone forgot to define (as well as declare) A::value
. std::min
takes its arguments by reference so A::value
must have an address so a reference can bind to it (technically, the one definition rule says it must be defined exactly once in the program.)
Nevermind, unary plus to the rescue:
int x = std::min(0, +A::value);
The unary plus creates a temporary with the same value, and the reference binds to the temporary, so we can work around the missing definition.
This isn't something you need often, but it is a practical use of the unary plus operator.