Don't return `const T`

Reason

It is not recommended to return a const value. Such older advice is now obsolete; it does not add value, and it interferes with move semantics.

Example

const vector<int> fct();    // bad: that "const" is more trouble than it is worth

void g(vector<int>& vx)
{
    // ...
    fct() = vx;   // prevented by the "const"
    // ...
    vx = fct(); // expensive copy: move semantics suppressed by the "const"
    // ...
}

The argument for adding const to a return value is that it prevents (very rare) accidental access to a temporary. The argument against is that it prevents (very frequent) use of move semantics.

See also: F.20, the general item about "out" output values

Enforcement

• Flag returning a const value. To fix: Remove const to return a non-const value instead.