Editing Inline expansion (section)

==Overview==
Inline expansion is similar to macro expansion as the compiler places a new copy of the function in each place it is called. Inlined functions run a little faster than the normal functions as function-calling-overheads are saved, however, there is a memory penalty. If a function is inlined 10 times, there will be 10 copies of the function inserted into the code. Hence inlining is best for small functions that are called often. In C++ the member functions of a class, if defined within the class definition, are inlined by default (no need to use the ''inline'' [[reserved word]] (keyword)); otherwise, the keyword is needed. The compiler may ignore the programmer’s attempt to inline a function, mainly if it is particularly large.

Inline expansion is used to eliminate the time overhead (excess time) when a function is called. It is typically used for functions that execute frequently. It also has a space benefit for very small functions, and is an enabling transformation for other [[Optimization (computer science)|optimizations]].

Without inline functions, the [[compiler]] decides which functions to inline. The programmer has little or no control over which functions are inlined and which are not. Giving this degree of control to the programmer allows for the use of application-specific knowledge in choosing which functions to inline.

Ordinarily, when a function is invoked, [[control flow|control]] is transferred to its definition by a [[branch (computer science)|branch]] or call instruction. With inlining, control drops through directly to the code for the function, without a branch or call instruction.

[[Compiler]]s usually implement [[Statement (computer science)|statements]] with inlining. Loop conditions and loop bodies need [[lazy evaluation]]. This property is fulfilled when the code to compute loop conditions and loop bodies is inlined. Performance considerations are another reason to inline statements.

In the context of [[functional programming]] languages, inline expansion is usually followed by the [[Lambda calculus#.CE.B2-reduction|beta-reduction]] transformation.

A programmer might inline a function manually through [[copy-and-paste programming]], as a one-time operation on the [[source code]]. However, other methods of controlling inlining (see below) are preferable, because they do not precipitate bugs arising when the programmer overlooks a (possibly modified) duplicated version of the original function body, while fixing a bug in the inlined function.