std::basic_format_arg<Context>::handle
| Defined in header <format>
|
||
| template< class Context > class basic_format_arg<Context>::handle; |
(since C++20) | |
A type-erased wrapper that allows formatting an object of a user-defined type.
handle objects are typically created by std::make_format_args and accessed through std::visit_format_arg or the visit member functions of std::basic_format_arg(since C++26).
Data members
A typical implementation of handle is TriviallyCopyable and only stores two non-static data members:
- a const void* pointer to the object to be formatted, and
- a void (*)(std::basic_format_parse_context<Context::char_type>&, Context&, const void*) function pointer to the function performing needed operations in the
formatmember function (see below).
Member functions
| format (C++20) |
formats the referenced object with the given contexts (public member function) |
std::basic_format_arg<Context>::handle::format
| void format( std::basic_format_parse_context<Context::char_type>& parse_ctx, Context& format_ctx ) const; |
(since C++20) | |
Let
-
Tbe the type of the formatting argument, -
TDbe std::remove_const_t<T>, -
TQbe const TD if const TD satisfies __formattable_with<Context> orTDotherwise, and -
refbe a reference to the formatting argument.
Equivalent to:
typename Context::template formatter_type<TD> f;
parse_ctx.advance_to(f.parse(parse_ctx));
format_ctx.advance_to(f.format(const_cast<TQ&>(static_cast<const TD&>(ref)), format_ctx));
Notes
A handle has reference semantics for the formatted argument and does not extend its lifetime. It is the programmer's responsibility to ensure that the argument outlives the handle. Usually, a handle is only used within formatting functions.
See also
| (C++20) |
class template that provides access to a formatting argument for user-defined formatters (class template) |
| (C++20)(C++20) |
creates a type-erased object referencing all formatting arguments, convertible to format_args (function template) |