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The following is a declaration of the concept "equality_comparable" from the <concepts> header of a C++20 standard library. This concept is satisfied by any type T such that for lvalues a and b of type T, the expressions a==b and a!=b as well as the reverse b==a and b!=a compile, and their results are convertible to a type that satisfies the concept "boolean-testable":
To elaborate on the above example, consider a base class with no virtual functions. Whenever the base class calls another member function, it will always call its own base class functions. When we derive a class from this base class, we inherit all the member variables and member functions that were not overridden (no constructors or destructors).
The STL includes classes that overload the function call operator (operator ()). Instances of such classes are called functors or function objects . Functors allow the behavior of the associated function to be parameterized (e.g. through arguments passed to the functor's constructor ) and can be used to keep associated per-functor state ...
In the C++ programming language, special member functions [1] are functions which the compiler will automatically generate if they are used, but not declared explicitly by the programmer. The automatically generated special member functions are: Default constructor if no other constructor is explicitly declared.
C++14 allows the lookup to be done via an arbitrary type, so long as the comparison operator can compare that type with the actual key type. [16] This would allow a map from std::string to some value to compare against a const char* or any other type for which an operator< overload is available.
If the object type is known, this may be bypassed by prepending a fully qualified class name before the function call, but in general calls to virtual functions are resolved at run time. In addition to standard member functions, operator overloads and destructors can be virtual. An inexact rule based on practical experience states that if any ...
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Function identity now also includes trailing requires-clauses (P1971) Constrained non-template functions have been removed <compare> is now available in freestanding implementations [134] std::spans typedef was changed from index_type to size_type to be consistent with the rest of the standard library [135]