Purpose of returning by const value?
It's pretty pointless to return a const
value from a function.
It's difficult to get it to have any effect on your code:
const int foo() {
return 3;
}
int main() {
int x = foo(); // copies happily
x = 4;
}
and:
const int foo() {
return 3;
}
int main() {
foo() = 4; // not valid anyway for built-in types
}
// error: lvalue required as left operand of assignment
Though you can notice if the return type is a user-defined type:
struct T {};
const T foo() {
return T();
}
int main() {
foo() = T();
}
// error: passing ‘const T’ as ‘this’ argument of ‘T& T::operator=(const T&)’ discards qualifiers
it's questionable whether this is of any benefit to anyone.
Returning a reference is different, but unless Object
is some template parameter, you're not doing that.
In the hypothetical situation where you could perform a potentially expensive non-const operation on an object, returning by const-value prevents you from accidentally calling this operation on a temporary. Imagine that +
returned a non-const value, and you could write:
(a + b).expensive();
In the age of C++11, however, it is strongly advised to return values as non-const so that you can take full advantage of rvalue references, which only make sense on non-constant rvalues.
In summary, there is a rationale for this practice, but it is essentially obsolete.