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### Mutable buffer sequence requirements

In the table below, `X` denotes a class containing objects of type `T`, `a` denotes a value of type `X` and `u` denotes an identifier.

Table 18. MutableBufferSequence requirements

expression | return type | assertion/note pre/post-condition
--- | --- | ---
`X::value_type` | `T` | `T` meets the requirements for ConvertibleToMutableBuffer.
`X::const_iterator` | iterator type pointing to `T` | `const_iterator` meets the requirements for bidirectional iterators (C++ Std, 24.1.4).

`X(a);`

post: `equal_mutable_buffer_seq(a, X(a))` where the binary predicate `equal_mutable_buffer_seq` is defined as

    bool equal_mutable_buffer_seq(
      const X& x1, const X& x2)
    {
      return
        distance(x1.begin(), x1.end())
          == distance(x2.begin(), x2.end())
            && equal(x1.begin(), x1.end(),
                     x2.begin(), equal_buffer);
    }

and the binary predicate `equal_buffer` is defined as

    bool equal_buffer(
      const X::value_type& v1,
      const X::value_type& v2)
    {
      mutable_buffer b1(v1);
      mutable_buffer b2(v2);
      return
        buffer_cast<const void*>(b1)
          == buffer_cast<const void*>(b2)
            && buffer_size(b1) == buffer_size(b2);
    }

`X u(a);`

post:

    distance(a.begin(), a.end())
      == distance(u.begin(), u.end())
        && equal(a.begin(), a.end(),
                 u.begin(), equal_buffer)

where the binary predicate `equal_buffer` is defined as

    bool equal_buffer(
      const X::value_type& v1,
      const X::value_type& v2)
    {
      mutable_buffer b1(v1);
      mutable_buffer b2(v2);
      return
        buffer_cast<const void*>(b1)
          == buffer_cast<const void*>(b2)
            && buffer_size(b1) == buffer_size(b2);
    }

`(&a)->~X();` | `void` | note: the destructor is applied to every element of `a`; all the memory is deallocated.
`a.begin();` | `const_iterator` or convertible to `const_iterator` |
`a.end();` | `const_iterator` or convertible to `const_iterator` |