4 A ['boxed value] is a type representing a constant value. It has a public static
5 `const` or `constexpr` member called `value`. The class represents that value as
6 a type, so it can be manipulated by [link metafunction template metafunction]s.
7 It has to be a [link metaprogramming_value template metaprogramming value].
9 For example the following `struct` represents the `true` value of type `bool`:
13 static constexpr bool value = true;
14 using type = true_type;
17 The `value` member is the wrapped value. `true_type::type` is an alias of
18 `true_type` which makes it a template metaprogramming value.