Question

What is inlining?

What is it used for?

Can you inline something in C#?

Answer 1

What it is

In the terms of C and C++ you use the inline keyword to tell the compiler to call a routine without the overhead of pushing parameters onto the stack. The Function instead has it’s machine code inserted into the function where it was called. This can create a significant increase in performance in certain scenarios.

Dangers

The speed benefits in using "inlining" decrease significantly as the size of the inline function increases. Overuse can actually cause a program to run slower. Inlining a very small accessor function will usually decrease code size while inlining a very large function can dramatically increase code size.

Inlining in C#

In C# inlining happens at the JIT level in which the JIT compiler makes the decision. There is currently no mechanism in C# which you can explicitly do this. If you wish to know what the JIT compiler is doing then you can call: System.Reflection.MethodBase.GetCurrentMethod().Name at runtime. If the Method is inlined it will return the name of the caller instead.

In C# you cannot force a method to inline but you can force a method not to. If you really need access to a specific callstack and you need to remove inlining you can use: MethodImplAttribute with MethodImplOptions.NoInlining. In addition if a method is declared as virtual then it will also not be inlined by the JIT. The reason behind this is that the final target of the call is unknown.

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