2 Pure functions
In this chapter you will learn
- why we need pure functions
- how to pass copies of the data
- how to recalculate instead of storing
- how to pass the state
- how to test pure functions
“Sometimes, the elegant implementation is just a function. Not a method. Not a class. Not a framework. Just a function.”
—John Carmack
Why do we need pure functions?
In the last chapter we learned about functions that don’t lie. Their signatures tell the whole story about their body. We concluded that these are the functions we can trust: the fewer surprises there are when we code, the fewer bugs there will be in the applications we create. In this chapter we will learn about the most trustworthy of all the functions that don’t lie: a pure function.
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