The sized_range concept refines range with
the requirement that the number of elements in the range can be determined
in amortized constant time using ranges::size.

```
template<class T>
concept sized_range =
range<T> && requires(T& t) { ranges::size(t); };
```

Given an lvalue t of type remove_reference_t<T>, T
models sized_range only if

- ranges::size(t) is amortized , does not modify t, and is equal to ranges::distance(ranges::begin(t), ranges::end(t)), and
- if iterator_t<T> models forward_iterator,
ranges::size(t) is well-defined regardless of the evaluation of
ranges::begin(t). [
*Note 1*:For example, it is possible for ranges::size(t) to be well-defined for a sized_range whose iterator type does not model forward_iterator only if evaluated before the first call to ranges::begin(t).â€”*end note*]

```
template<class>
constexpr bool disable_sized_range = false;
```

Such specializations shall
be usable in constant expressions ([expr.const]) and
have type const bool.

[*Note 2*: *end note*]

disable_sized_range allows use of range types with the library
that satisfy but do not in fact model sized_range.

â€”