CODEWITHSUNDEEP
c++templatesc++11decltype
André Puel
André Puel

Reputation: 9179

Decltype for return of a function

I am making a templated class that is a wrapper around any iterator. I am making the operator* this way:

template <typename T>
class MyIterator {
public:
    //...
    decltype(*T()) operator*() {
    //...
    }
}

I give decltype a invocation to operator* of class T, and it even works, but if T doesnt have default constructor it wont work.

Is there anyway to find out the returned type of a function/method ?

Upvotes: 10

Views: 6318

Answers (1)

James McNellis
James McNellis

Reputation: 354969

This is what std::declval is for:

decltype(*std::declval<T>()) operator*() { /* ... */ }

If your implementation does not provide std::declval (Visual C++ 2010 does not include it), you can easily write it yourself:

template <typename T>
typename std::add_rvalue_reference<T>::type declval(); // no definition required

Since T is an iterator type, you could also use the std::iterator_traits template, which does not require any C++0x support:

typename std::iterator_traits<T>::reference operator*() { /* ... */ }

Upvotes: 17

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