2013/8/4 Edward Diener <eldiener@tropicsoft.com>
On 8/4/2013 8:57 AM, gast128 wrote: Returning a 'const X' is meaningless. Just return 'X' instead.
Just to clarify, Edward, I think you're wrong. Consider: struct X { void go() {} }; X source_a(); X const source_b(); int main() { source_a().go(); // ok source_b().go(); // error
The same goes for passing something as 'const X'.
I assume you mean a function *taking* something as 'const X'. Consider: void g( X x ); void g( X const x ); The two declarations of g() are equivalent (!), so you could say this 'const' is meaningless ;-). The 'const' here matters in the implementation of function g. void f( X x, X const y ) { x.go(); // ok y.go(); // error
When you pass or return by value you get a copy of the object being passed so it means nothing to say that the object is 'const'.
Considering what I've written above, I disagree that 'const' means nothing here. When function source_b() returns by const value, it *means* the returned temporary is const. When function f() takes by const value, it *means* the implementation of f() doesn't modify the copy it gets. For the caller of f(), this 'const' is meaningless indeed ;-) Regards, Kris