Clang modifies return value in destructor?

Question

While trying to write a class that times the duration between calling it\'s constructor and destructor, I ran into what I think is a bug in clang. (Edit: it\'s not a bug; it

Answer 1

Short answer: due to NRVO, the output of the program may be either 0 or the actual duration. Both are valid.

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For background, see first:

• in C++ which happens first, the copy of a return object or local object's destructors?
• What are copy elision and return value optimization?

Guideline:

• Avoid destructors that modify return values.

For example, when we see the following pattern:

T f() {
    T ret;
    A a(ret);   // or similar
    return ret;
}

We need to ask ourselves: does A::~A() modify our return value somehow? If yes, then our program most likely has a bug.

For example:

• A type that prints the return value on destruction is fine.
• A type that computes the return value on destruction is not fine.