What is the Lifetime of a Braced-Init-List Returned from a C Function?

Lifetime of a Braced-Init-List Return Value

In C , returning a braced-init-list from a function raises questions about the lifetime of the initializer_list and its underlying array.

Problem Outline

Previous analysis suggests that GCC incorrectly terminates the initializer_list array before the end of the return expression, while Clang incorrectly preserves objects without ever destructing them.

Standardese Interpretation

According to the C 11 standard, a return statement with a braced-init-list initializes the return value through copy-list-initialization. If the return type is a specialization of std::initializer_list, an initializer_list object is constructed and initialized from the specified list.

Array Lifetime

The constructed initializer_list stores a reference to an array of elements initialized from the initializer list. The array's lifetime is defined to be the same as the initializer_list object. This means that in the return statement, the underlying array is initialized from the braced-init-list and has a lifetime extending into the calling scope.

Correct Implementation

Therefore, the expected behavior is that the initializer_list's array should persist into the calling function, allowing for its further use or binding to a named reference. However, GCC's current implementation prematurely deallocates the array, violating this expectation.

Additional Clarifications

• Returning a braced-init-list does not imply a copy-construction of the returned object. It simply uses copy-list-initialization to initialize the return value.
• DR 1290 has revised the wording related to initializer_list lifetime, and DR 1565 and 1599 are also under consideration, potentially bringing further changes.
• Binding an additional reference to the initializer_list does not extend the lifetime of its underlying array, similar to how a reference to a temporary object does not extend the temporary's lifetime.

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