This template can be used by implementations to enable efficient implementations of std::print and std::println.

If std::enable_nonlocking_formatter_optimization<T> is true, printing an argument of type T can be performed in a more efficient way (see std::print for details). std::enable_nonlocking_formatter_optimization specializations can be true in the following cases:

• T is one of the types where std::formatter<T, CharT> is a basic standard specialization or standard specialization for a library type (see below).
• A program may specialize this template for any cv-unqualified program-defined type T. Such specializations must be usable in constant expressions and have type const bool.

Basic standard specializations

In the following list, CharT is either char or wchar_t, ArithmeticT is any cv-unqualified arithmetic type other than char, wchar_t, char8_t, char16_t, or char32_t:

Standard specializations for library types

Specializations of enable_nonlocking_formatter_optimization for all specializations of the following standard templates are defined as true:

• std::chrono::zoned_time when its template parameter type TimeZonePtr is const std::chrono::time_zone*

Specializations of enable_nonlocking_formatter_optimization for all specializations of the following standard templates are defined as conditionally true:

• std::pair
• std::tuple
• std::chrono::duration

Specialization of enable_nonlocking_formatter_optimization for all formattable range types are always defined as false for which the range format kind is not std::range_format::disabled.

Notes

See also