Programming Kotlin

Pure functions

In functional programming, the concept of a pure function is one that holds the following two properties:

• The function should always return the same output for the same input
• The function should not create any side effects

The first property means that when a function is invoked, the value returned should always be the same whenever the same input is used. A simple example is abs. The absolute value of an integer is always the same for the same input. A pure function can depend only on the input, but it does not have to necessarily use all the input types.

The second property is that a function should not cause any observable changes outside the function. So the function cannot depend on any external mutable state, change variables ...