Call by reference

Call by reference

Call by reference (or pass by reference) is an evaluation strategy where a parameter is bound to an implicit reference to the variable used as argument, rather than a copy of its value. This typically means that the function can modify (i.e., assign to) the variable used as argument—something that will be seen by its caller. Call by reference can therefore be used to provide an additional channel of communication between the called function and the calling function. Pass by reference can significantly improve performance: calling a function with a many-megabyte structure as an argument does not have to copy the large structure, only the reference to the structure (which is generally a machine word and only a few bytes). However, a call-by-reference language makes it more difficult for a programmer to track the effects of a function call, and may introduce subtle bugs.