A few days ago, I faced the following issue: We have a method that should return if all items of an array have some specific characteristic, for example:
struct Product {
let price: Double
}
func allProductsHaveValueGreaterThan50(_ products: [Product]) -> Bool {
// ...
}
The first solution was pretty simple:
func allProductsHaveValueGreaterThan50(_ products: [Product]) -> Bool {
guard products.isEmpty == false else { return false }
var allProductsHaveValueGreaterThan50 = true
products.forEach {
if $0.price <= 50 {
allProductsHaveValueGreaterThan50 = false
return
}
}
return allProductsHaveValueGreaterThan50
}
Another way to do that is by using a filter and check if the filtered array and products have the same size:
func allProductsHaveValueGreaterThan50(_ products: [Product]) -> Bool {
guard products.isEmpty == false else { return false }
let productsThatPriceIsGreaterThan50 = products.filter { $0.price > 50 }
return products.count == productsThatPriceIsGreaterThan50.count
}
That one ☝️ will work like expected, but we can simplify using allSatisfy:
func allProductsHaveValueGreaterThan50(_ products: [Product]) -> Bool {
guard products.isEmpty == false else { return false }
return products.allSatisfy { $0.price > 50 }
}
Conclusion and some thoughts
allSatisfy method is a capability of Array that is available since Swift 5.1, the syntax is pretty clear and will help us to remove all methods like I have presented here to solve this kind of issue. If you use allSatisfy in an empty collection you will get true as result, what could be weird for a moment but here there’s a good explanation about.
If you don’t want to check array size every time, you can create an extension to encapsulate this rule:
extension Array {
func allSatisfyAndIsNotEmpty(_ predicate: (Element) throws -> Bool) rethrows -> Bool {
guard self.isEmpty == false else { return false }
return try self.allSatisfy(predicate)
}
}
func allProductsHaveValueGreaterThan50(_ products: [Product]) -> Bool {
return products.allSatisfyAndIsNotEmpty { $0.price > 50 }
}
References
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