Concepts

ConstFunctionObject

Is an object with a const call operator:

concept ConstFunctionObject
{
    template<class... Ts>
    auto operator()(Ts&&...) const;
};

Requirements:

The type F satisfies ConstFunctionObject if

• The type F satisfies std::is_object, and

Given

• f, an object of type const F
• args..., suitable argument list, which may be empty

Expression	Requirements
f(args...)	performs a function call

NullaryFunctionObject

Is an object with a const call operator that accepts no parameters:

concept NullaryFunctionObject
{
    auto operator()() const;
};

Requirements:

• ConstFunctionObject

Given

• f, an object of type const F

Expression	Requirements
f()	performs a function call

UnaryFunctionObject

Is an object with a const call operator that accepts one parameter:

concept UnaryFunctionObject
{
    template<class T>
    auto operator()(T&&) const;
};

Requirements:

• ConstFunctionObject

Given

• f, an object of type const F
• arg, a single argument

Expression	Requirements
f(arg)	performs a function call

BinaryFunctionObject

Is an object with a const call operator that accepts two parameter:

concept UnaryFunctionObject
{
    template<class T, class U>
    auto operator()(T&&, U&&) const;
};

Requirements:

• ConstFunctionObject

Given

• f, an object of type const F
• arg1, a single argument
• arg2, a single argument

Expression	Requirements
f(arg1, arg2)	performs a function call

MutableFunctionObject

Is an object with a mutable call operator:

concept MutableFunctionObject
{
    template<class... Ts>
    auto operator()(Ts&&...);
};

Requirements:

The type F satisfies MutableFunctionObject if

• The type F satisfies std::is_object, and

Given

• f, an object of type F
• args..., suitable argument list, which may be empty

Expression	Requirements
f(args...)	performs a function call

EvaluatableFunctionObject

Is an object that is either a NullaryFunctionObject, or it is an UnaryFuntionObject that accepts the identity function as a parameter.

Requirements:

• NullaryFunctionObject

Given

• f, an object of type const F

Expression	Requirements
f()	performs a function call

Or:

• UnaryFuntionObject

Given

• f, an object of type const F
• identity, which is the identity function

Expression	Requirements
f(identity)	performs a function call

Invocable

Is an object for which the INVOKE operation can be applied.

Requirements:

The type T satisfies Invocable if

Given

• f, an object of type T
• Args..., suitable list of argument types

The following expressions must be valid:

Expression	Requirements
INVOKE(f, std::declval<Args>()...)	the expression is well-formed in unevaluated context

where INVOKE(f, x, xs...) is defined as follows:

• if f is a pointer to member function of class U:
  • If std::is_base_of<U, std::decay_t<decltype(x)>>() is true, then INVOKE(f, x, xs...) is equivalent to (x.*f)(xs...)
  • otherwise, if std::decay_t<decltype(x)> is a specialization of std::reference_wrapper, then INVOKE(f, x, xs...) is equivalent to (x.get().*f)(xs...)
  • otherwise, if x does not satisfy the previous items, then INVOKE(f, x, xs...) is equivalent to ((*x).*f)(xs...).
• otherwise, if f is a pointer to data member of class U:
  • If std::is_base_of<U, std::decay_t<decltype(x)>>() is true, then INVOKE(f, x) is equivalent to x.*f
  • otherwise, if std::decay_t<decltype(x)> is a specialization of std::reference_wrapper, then INVOKE(f, x) is equivalent to x.get().*f
  • otherwise, if x does not satisfy the previous items, then INVOKE(f, x) is equivalent to (*x).*f
• otherwise, INVOKE(f, x, xs...) is equivalent to f(x, xs...)

ConstInvocable

Is an object for which the INVOKE operation can be applied.

Requirements:

The type T satisfies ConstInvocable if

Given

• f, an object of type const T
• Args..., suitable list of argument types

The following expressions must be valid:

Expression	Requirements
INVOKE(f, std::declval<Args>()...)	the expression is well-formed in unevaluated context

where INVOKE(f, x, xs...) is defined as follows:

• if f is a pointer to member function of class U:
  • If std::is_base_of<U, std::decay_t<decltype(x)>>() is true, then INVOKE(f, x, xs...) is equivalent to (x.*f)(xs...)
  • otherwise, if std::decay_t<decltype(x)> is a specialization of std::reference_wrapper, then INVOKE(f, x, xs...) is equivalent to (x.get().*f)(xs...)
  • otherwise, if x does not satisfy the previous items, then INVOKE(f, x, xs...) is equivalent to ((*x).*f)(xs...).
• otherwise, if f is a pointer to data member of class U:
  • If std::is_base_of<U, std::decay_t<decltype(x)>>() is true, then INVOKE(f, x) is equivalent to x.*f
  • otherwise, if std::decay_t<decltype(x)> is a specialization of std::reference_wrapper, then INVOKE(f, x) is equivalent to x.get().*f
  • otherwise, if x does not satisfy the previous items, then INVOKE(f, x) is equivalent to (*x).*f
• otherwise, INVOKE(f, x, xs...) is equivalent to f(x, xs...)

UnaryInvocable

Is an object for which the INVOKE operation can be applied with one parameter.

Requirements:

• ConstInvocable

Given

• f, an object of type const F
• arg, a single argument

Expression	Requirements
INVOKE(f, arg)	the expression is well-formed in unevaluated context

BinaryInvocable

Is an object for which the INVOKE operation can be applied with two parameters.

Requirements:

• ConstInvocable

Given

• f, an object of type const F
• arg1, a single argument
• arg2, a single argument

Expression	Requirements
INVOKE(f, arg1, arg2)	the expression is well-formed in unevaluated context

Metafunction

Given

• f, a type or a template
• args..., any suitable type, which may be empty

Expression	Requirements
f::type	The type is the result of the metafunction
f<args...>::type	The type is the result of the metafunction

MetafunctionClass

Given

• f, a type or a template
• args..., any suitable type, which may be empty

Expression	Requirements
f::apply::type	The type is the result of the metafunction
f::apply<args...>::type	The type is the result of the metafunction