A mutable size sequence is a range into which an operation, such as the receive_multiple operation of a datagram socket, writes the number of bytes received in each datagram.

A type X meets the MutableSizeSequence requirements if it satisfies the requirements of Destructible (C++Std [destructible]) and CopyConstructible (C++Std [copyconstructible]), and is_shallow_mutable_sequence<X>::value is true, as well as the additional requirements listed below.

In the table below, x denotes a value of type X, or of type R if X is std::reference_wrapper<R>, i denotes an iterator in the range [x.begin(),x.end()), e denotes *i, or (*i).get() if *i is a std::reference_wrapper, and v denotes a value of type std::size_t.