Function Composition
Function composition chains two functions so that the output of one goes into the next, like an assembly line. andThen and compose join them in either order.
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Syntax
val combined1 = f andThen g // g(f(x))
val combined2 = f compose g // f(g(x))Function Composition
andThen and compose combine two functions into a new one: f andThen g runs f first then feeds its result into g, while f compose g runs g first then feeds its result into f -- the opposite order.
This lets you build complex transformations out of small, reusable, single-purpose functions. Composition is a hallmark of functional programming style, favoring small pieces glued together over one large function.
Note:
f andThen gapplies f then g (left to right).f compose gapplies g then f (right to left) -- easy to mix up.
Example: Function Composition
object Main extends App {
val addOne: Int => Int = _ + 1
val double: Int => Int = _ * 2
val addThenDouble = addOne andThen double
val doubleThenAdd = addOne compose double
println(addThenDouble(3)) // (3+1)*2 = 8
println(doubleThenAdd(3)) // (3*2)+1 = 7
}Login to try C/C++/Java/PHP code in the editor
Related Topics
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Common Mistakes
- Mixing up
andThenandcompose, whenf andThen grunsffirst andf compose grunsgfirst. - Composing functions whose types do not match, such as a
Stringresult feeding anIntfunction. - Forgetting that the result is a new function and must still be called with an argument.
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