Mastering High Performance with Kotlin

Function composition

Function composition is a feature of functional programming that allows you to write simple and reliable code with significant performance improvements as compared with chain of function's invocations. 

To avoid code such as this:

students        .filter(::ageMoreThan20)        .filter(::firstNameStartsWithE)        .filter(::theLengthOfSecondNameMoreThan5)

You can write something like this:

fun predicate(student: Student)         = ageMoreThan20(student)         && firstNameStartsWithE(student)         && theLengthOfSecondNameMoreThan5(student)students.filter(::predicate)

Or you can create your function to implement function composition. This function may look like this:

inline infix fun <P> ((P) -> Boolean).and(crossinline predicate: (P) -> Boolean): (P) -> ...