Copying all of a Function body into another function rather than just calling it. This may have several benefits (such as avoiding the FunctionCall/return overhead, and constant evaluation of the inlined function).
Disadvantages of having some code inlined in many places (instead of as a single function) can include a larger binary, and cache misses during execution.
Inlining is one of the easiest global optimisations in procedural languages such as C/C++ and Java.
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