# std::ranges::sized_range, std::ranges::disable_sized_range

< cpp‎ | ranges
 Defined in header  template< class T > concept sized_range = ranges::range &&   requires(T& t) {     ranges::size(t);   }; (1) (since C++20) template inline constexpr bool disable_sized_range = false; (2) (since C++20)
1) The sized_range concept specifies the requirements of a range type that knows its size in constant time with the size function.
2) disable_sized_range exists to allows use of range types that provide a size function (either as a member or as a non-member) but do not in fact model sized_range. Users may specialize disable_sized_range for cv-unqualified program-defined types. Such specializations shall be usable in constant expressions and have type const bool.

### Semantic requirements

1) Given an lvalue t of type , T models sized_range only if
• has amortized constant-time complexity,
• does not alter the value of t in a manner observable to equality-preserving expressions, and
• is equal to , and
• if models forward_iterator, ranges::size(t) is well-defined regardless of the evaluation of (in other words, a single-pass sized range may support a call to size only before the first call to begin, but a forward range must support size at all times)

### Notes

disable_sized_range cannot be used to opt-out a range whose iterator and sentinel satisfy sized_sentinel_for; disable_sized_sentinel_for must be used instead.

disable_sized_range cannot be specialized for array types or reference types.