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Implicit type conversion, also known as coercion or type juggling, is an automatic type conversion by the compiler. Some programming languages allow compilers to provide coercion; others require it. In a mixed-type expression, data of one or more subtypes can be converted to a supertype as needed at runtime so that the program will run correctly.
The type parameter must be a data type to which object can be converted via a known method, whether it be a builtin or a cast. The type can be a reference or an enumerator. All types of conversions that are well-defined and allowed by the compiler are performed using static_cas
explicit K:: operator R (); since C++11 — Note: for user-defined conversions, the return type implicitly and necessarily matches the operator name unless the type is inferred (e.g. operator auto (), operator decltype (auto)() etc.). dynamic cast conversion dynamic_cast<R>(a) No: No — const_cast conversion const_cast<R>(a) No: No ...
For example, suppose that a program defines two types, A and B, where B is a subtype of A. If the program tries to convert a value of type A to type B, which is known as downcasting, then the operation is legal only if the value being converted is actually a value of type B. Thus, a dynamic check is needed to verify that the operation is safe.
In programming languages that support generics (a.k.a. parametric polymorphism), the programmer can extend the type system with new constructors. For example, a C# interface like IList < T > makes it possible to construct new types like IList < Animal > or IList < Cat >. The question then arises what the variance of these type constructors ...
In class-based programming, downcasting, or type refinement, is the act of casting a base or parent class reference, to a more restricted derived class reference. [1] This is only allowable if the object is already an instance of the derived class, and so this conversion is inherently fallible.
Autoboxing is the term for getting a reference type out of a value type just through type conversion (either implicit or explicit). The compiler automatically supplies the extra source code that creates the object. For example, in versions of Java prior to J2SE 5.0, the following code did not compile:
In C and C++, constructs such as pointer type conversion and union — C++ adds reference type conversion and reinterpret_cast to this list — are provided in order to permit many kinds of type punning, although some kinds are not actually supported by the standard language.