is-integer-like , is-signed-integer-like

 

C++

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Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) is-integer-like is-signed-integer-like (C++20)(C++20)	sentinel_for (C++20) sized_sentinel_for (C++20) input_iterator (C++20) output_iterator (C++20) input_or_output_iterator (C++20)	forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)	iterator (deprecated in C++17) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (C++20)
Algorithm concepts and utilities
Indirect callable concepts
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20)	indirect_unary_predicate (C++20) indirect_binary_predicate (C++20)	indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
Common algorithm requirements
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20)	indirectly_copyable_storable (C++20)   indirectly_swappable (C++20) indirectly_comparable (C++20)	permutable (C++20) mergeable (C++20) sortable (C++20)
Utilities
indirect_result_t (C++20)	projected (C++20)	projected_value_t (C++26)
Iterator adaptors
reverse_iterator make_reverse_iterator (C++14) move_iterator (C++11) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)	front_insert_iterator back_insert_iterator inserter insert_iterator front_inserter back_inserter move_sentinel (C++20)	common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) make_const_iterator (C++23) make_const_sentinel (C++23)
Stream iterators istream_iterator    ostream_iterator istreambuf_iterator ostreambuf_iterator	Iterator customization points ranges::iter_move (C++20) ranges::iter_swap (C++20)
Iterator operations advance distance prev (C++11)   next (C++11) ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)	Range access begincbegin (C++11)(C++14) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) empty (C++17) data (C++17)

 

template< class T > constexpr bool /*is-integer-like*/ = /* see description */;	(1)	(since C++20) (exposition only*)
template< class T > constexpr bool /*is-signed-integer-like*/ = /* see description */;	(2)	(since C++20) (exposition only*)

1) /*is-integer-like*/<T> is true if and only if T is an integer-like type.

2) /*is-signed-integer-like*/<T> is true if and only if T is a signed-integer-like type.

Integer-class type

A type T is an integer-class type if it is in a set of implementation-defined types that behave as integer types do, as defined below. An integer-class type is not necessarily a class type.

An integer-class type can represent \(\scriptsize 2^N \)2N
consecutive integers, where N, a positive integer, is called the width of the integer-class type.

An integer-class type is either signed or unsigned:

• A signed integer class type can represent all integers in [\(\scriptsize -2^{N-1} \)-2N-1
  , \(\scriptsize 2^{N-1}-1 \)2N-1
  -1], where N is greater than the width of every signed integral type.
• An unsigned integer class type can represent all integers in [\(\scriptsize 0 \)0, \(\scriptsize 2^N-1 \)2N
  -1], where N is greater than the width of every unsigned integral type.

All integer-class types model regular and three_way_comparable<std::strong_ordering>.

A value-initialized object of integer-class type has value ​0​.

An expression E of integer-class type T is contextually convertible to bool as if by bool(E != T(0)).

Integer-like type

A type other than (possibly cv-qualified) bool is integer-like if it models integral or if it is an integer-class type.

• An integer-like type is signed-integer-like if it models signed_integral or if it is a signed-integer-class type.
• An integer-like type is unsigned-integer-like if it models unsigned_integral or if it is an unsigned-integer-class type.

Required behaviors

Expressions of integer-class type are explicitly convertible to any integer-like type, and implicitly convertible to any integer-class type of equal or greater width and the same signedness. Expressions of integral type are both implicitly and explicitly convertible to any integer-class type. Conversions between integral and integer-class types and between two integer-class types do not exit via an exception. The result of such a conversion is the unique value of the destination type that is congruent to the source modulo \(\scriptsize 2^N \)2N
, where N is the width of the destination type.

Let Int<T> denote the following type:

• If T is an integer-class type, Int<T> is a unique hypothetical extended integer type of the same signedness with the same width as T.
• If T is an integral type, let Int<T> is the same type as T.

Given the following types, values and operators:

Type	Definition
IC	an integer-class type
IL	an integer-like type
Value	Definition
a	an object of type IC
b	an object of type IL
c	an lvalue of an integeral type
x	an object of type Int<IC> that represent the same value as a
y	an object of type Int<IL> that represent the same value as b
Operator	Definition
@=	one of +=, -=, *=, /=, %=, &=, |=, ^=, <<= and >>=
@	one of +, -, *, /, %, &, |, ^, <<, >>, &&, ||, ==, !=, <, >, <=, >=, <=> and ,

The following expressions must be well-formed and have their specified result and effects if the specified conditions are satisfied:

Expression	Condition	Result	Effects
a++	No condition	a prvalue of type IC whose value is equal to that of a prior to the evaluation	modifies the value of a by adding 1 to it
a--			modifies the value of a by subtracting 1 to it
++a	expression-equivalent to a += 1
--a	expression-equivalent to a -= 1
&a	expression-equivalent to std::addressof(a)
!a	!x is well-formed	same as !x
+a	+x is well-formed	same as +x, but has type IC	same as +x
-a	-x is well-formed	same as -x, but has type IC	same as -x
~a	~x is well-formed	same as ~x, but has type IC	same as ~x
c @= a	c @= x is well-formed	an lvalue referring to c	same as c @= x
a @= b	x @= y is well-formed	an lvalue referring to a	same as x @= y, except that the value that would be stored into x is stored into a
a @ b	x @ y is well-formed	same as x @ y, but the result type is different: If x @ y is of type Int<IC>, the result has type IC. If x @ y is of type Int<IL>, the result has type IL. If x @ y is of any other type T, the result has type T.	same as x @ y
b @ a	y @ x is well-formed	same as y @ x, but the result type is different: If y @ x is of type Int<IC>, the result has type IC. If y @ x is of type Int<IL>, the result has type IL. If y @ x is of any other type T, the result has type T.	same as y @ x

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3366 (P2393R1)	C++20	the conversion between an integer-class type and its corresponding integer type was not guaranteed to produce a representable value	guaranteed
LWG 3376 (P2393R1)	C++20	integer-class types could only be class types	also allowed non-class types
LWG 3467	C++20	bool was considered as an integer-like type	excluded
LWG 3575 (P2393R1)	C++20	integer-class types were not guaranteed to be three-way-comparable	guaranteed

See also

weakly_incrementable (C++20)

specifies that a semiregular type can be incremented with pre- and post-increment operators (concept)