Swift 3 - Decrease Collection of Objects by Int Object
I have an array containing 3 objects:
class AClass {
var distance: Int?
}
let obj0 = AClass()
obj0.distance = 0
let obj1 = AClass()
obj1.distance = 1
let obj2 = AClass()
obj2.distance = 2
let arr = [obj0, obj1, obj2]
When I decrease the array and assign it to a variable, I can only sum the last element in the array.
let total = arr.reduce(0, {$1.distance! + $1.distance!}) //returns 4
If I try $ 0.distance! these are errors with "expression is ambiguous without additional context".
I tried to be more explicit:
var total = arr.reduce(0, {(first: AClass, second: AClass) -> Int in
return first.distance! + second.distance!
})
But these errors with "Int" are incompatible with the contextual type "_" "How to reduce it to the sum of the distances?
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1 answer
var total = arr.reduce(0, {$0 + $1.distance!})
The first argument is the accumulator, it is already an integer.
Note that this will crash on elements with no distance. You can fix this for example. through:
let total = arr.reduce(0, {$0 + ($1.distance ?? 0)})
or
let total = arr.flatMap { $0.distance }.reduce(0, +)
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