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In assembly, C, C++, Pascal, Modula2 and other languages, a callback function is stored internally as a function pointer. Using the same storage allows different languages to directly share callbacks without a design-time or runtime interoperability layer. For example, the Windows API is accessible via multiple languages, compilers and assemblers.
In object-oriented programming languages, it is possible to use method chaining to simulate named parameters, as a form of fluent interface. Each named-parameter argument is replaced with a method on an "arguments" object that modifies and then returns the object. In C++, this is termed the named parameter idiom. [17]
A function pointer, also called a subroutine pointer or procedure pointer, is a pointer referencing executable code, rather than data. Dereferencing the function pointer yields the referenced function, which can be invoked and passed arguments just as in a normal function call.
When discussing the code inside the subroutine definition, the variables in the subroutine's parameter list are the parameters, while the values of the parameters at runtime are the arguments. For example, in C, when dealing with threads it is common to pass in an argument of type void* and cast it to an expected type:
The reference to the object is passed as a hidden argument, usually accessible from within the method as this. A parameter called by reference is syntactic sugar for technically passing a pointer as the parameter, but syntactically handling it as the variable itself, to avoid constant pointer de-referencing in the code inside the function.
Call by address, pass by address, or call/pass by pointer is a parameter passing method where the address of the argument is passed as the formal parameter. Inside the function, the address (pointer) may be used to access or modify the value of the argument. For example, the swap operation can be implemented as follows in C: [46]
For example, given a function that takes a string containing an HTML template and returns equivalent D source code, it is possible to use it in the following way: // Import the contents of example.htt as a string manifest constant. enum htmlTemplate = import ( "example.htt" ); // Transpile the HTML template to D code. enum htmlDCode ...
For example, vfprintf() is an alternate version of fprintf() expecting a va_list instead of the actual unnamed argument list. A user-defined variadic function can therefore initialize a va_list variable using va_start and pass it to an appropriate standard library function, in effect passing the unnamed argument list by reference instead of ...