F# has features of inline functions since F# 1.9, although the previous version already had it as experimental.
The definition of inline function is quite non-trivial: an inline function is a function that is integrated into the calling code. The word integrated must have a clear context; what kind of integration? It is integrated in the sense that the type is not generalized, but it is compiled accordingly when the inline function is used within other functions. The inline function body is embedded directly. This function embedding will be discussed in detail in the next section.
Before we discuss in-depth about inline functions, let's first examine the background of the importance and relevance of inline functions in the next section.