Can You Move Elements Out of a std::initializer_list?

Initializer Lists and Move Semantics: Can I Move Elements Out?

A question arises regarding the usage of initializer lists and move semantics: is it permissible to move elements out of a std::initializer_list? Let's investigate this further.

The Problem

Consider the following code snippet:

#include <initializer_list>
#include <utility>

template<typename T>
void foo(std::initializer_list<T> list)
{
    for (auto it = list.begin(); it != list.end(); ++it)
    {
        bar(std::move(*it));   // kosher?
    }
}

Here, we want to check if it's possible to move elements out of a std::initializer_list.

The Answer

Surprisingly, the answer is no. The expression std::move(*it) will not result in a move. Instead, it produces an immutable rvalue reference of type T const &&. This is because initializer_list's begin and end methods return const T *, which doesn't allow for move semantics.

The likely reason for this is to enable the compiler to create initializer_list as a statically-initialized constant. However, it would be more intuitive to have begin and end return either initializer_list or const initializer_list, depending on the compiler's discretion.

Further Considerations

An ISO proposal has been made to provide initializer_list support for move-only types. This proposal, though still in its early stages, addresses the issue raised here.

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