- Swift Functional Programming(Second Edition)
- Dr. Fatih Nayebi
- 392字
- 2021-07-02 23:54:32
Higher-order functions
As we have seen in the Defining and using function parameters and Function types sections of this chapter, functions can accept functions as parameters in Swift. Functions that can accept other functions as parameters are called higher-order functions. This concept, along with first-class functions, empowers FP and function decomposition.
As this topic is essential in FP, we will go through another simple example.
Suppose that we need to develop two functions that add and subtract two Int values as follows:
func subtractTwoValues(a: Int, b: Int) -> Int {
return a - b
}
func addTwoValues(a: Int, b: Int) -> Int {
return a + b
}
Also, we need to develop functions to calculate the square and triple of two Int values as follows:
func square(a: Int) -> Int {
return a * a
}
func triple(a: Int) -> Int {
return a * a * a // or return square(a) * a
}
Suppose we need another function that subtracts the two squared values:
func subtractTwoSquaredValues(a: Int, b: Int) -> Int {
return (a * a) - (b * b)
}
In case we needed to add two squared values:
func addTwoSquaredValues(a: Int, b: Int) -> Int {
return (a * a) + (b * b)
}
Let's say that we need another function that triples a value and multiplies it with another tripled value:
func multiplyTwoTripledValues(a: Int, b: Int) -> Int {
return (a * a * a) * (b * b * b)
}
This way, we had to write a lot of redundant and inflexible functions. Using higher-order functions, we could write a flexible function as follows:
typealias AddSubtractOperator = (Int, Int) -> Int
typealias SquareTripleOperator = (Int) -> Int
func calculate(a: Int,
b: Int,
funcA: AddSubtractOperator,
funcB: SquareTripleOperator) -> Int {
return funcA(funcB(a), funcB(b))
}
This higher-order function takes two other functions as parameters and uses them. We can call it for different scenarios as follows:
print("The result of adding two squared values is: \(calculate(a: 2, b: 2, funcA: addTwoValues, funcB: square))")
// prints "The result of adding two squared value is: 8"
print("The result of subtracting two tripled value is: \(calculate(a: 3, b: 2, funcA: subtractTwoValues, funcB: triple))")
// prints "The result of adding two tripled value is: 19"
This simple example presented the utility of higher-order functions in function composition and subsequently in program modularity.
- Python數(shù)據(jù)挖掘:入門、進(jìn)階與實(shí)用案例分析
- SQL Server入門經(jīng)典
- 大數(shù)據(jù)可視化
- Access 2007數(shù)據(jù)庫應(yīng)用上機(jī)指導(dǎo)與練習(xí)
- 數(shù)據(jù)庫原理與應(yīng)用(Oracle版)
- Oracle 12c云數(shù)據(jù)庫備份與恢復(fù)技術(shù)
- 高維數(shù)據(jù)分析預(yù)處理技術(shù)
- INSTANT Apple iBooks How-to
- Visual FoxPro數(shù)據(jù)庫技術(shù)基礎(chǔ)
- 計(jì)算機(jī)視覺
- 利用Python進(jìn)行數(shù)據(jù)分析(原書第2版)
- Deep Learning with R for Beginners
- Scratch 2.0 Game Development HOTSHOT
- 數(shù)據(jù)會(huì)說話:活用數(shù)據(jù)表達(dá)、說服與決策
- Swift 2 By Example