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How do you do "inline functions" in C#? I don't think I understand the concept. Are they like anonymous methods? Like lambda functions?
Note: The answers almost entirely deal with the ability to inline functions, i.e. "a manual or compiler optimization that replaces a function call site with the body of the callee." If you are interested in anonymous (a.k.a. lambda) functions, see @jalf's answer or What is this 'Lambda' everyone keeps speaking of?.
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An inline function is one for which the compiler copies the code from the function definition directly into the code of the calling function rather than creating a separate set of instructions in memory. This eliminates call-linkage overhead and can expose significant optimization opportunities.
C++ and C99, but not its predecessors K&R C and C89, have support for inline functions, though with different semantics. In both cases, inline does not force inlining; the compiler is free to choose not to inline the function at all, or only in some cases.
The inline keyword tells the compiler to substitute the code within the function definition for every instance of a function call. Using inline functions can make your program faster because they eliminate the overhead associated with function calls.
Inline functions are commonly used when the function definitions are small, and the functions are called several times in a program. Using inline functions saves time to transfer the control of the program from the calling function to the definition of the called function.
Finally in .NET 4.5, the CLR allows one to hint/suggest1 method inlining using MethodImplOptions.AggressiveInlining value. It is also available in the Mono's trunk (committed today).
// The full attribute usage is in mscorlib.dll,
// so should not need to include extra references
using System.Runtime.CompilerServices;
...
[MethodImpl(MethodImplOptions.AggressiveInlining)]
void MyMethod(...)
1. Previously "force" was used here. I'll try to clarify the term. As in the comments and the documentation, The method should be inlined if possible. Especially considering Mono (which is open), there are some mono-specific technical limitations considering inlining or more general one (like virtual functions). Overall, yes, this is a hint to compiler, but I guess that is what was asked for.
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