CODEWITHSUNDEEP
swift
Tom Wayne
Tom Wayne

Reputation: 57

Shouln't this be a var instead of let?

Hi guys so I have an issue with understanding this code: 

struct Point {
    // Passing in values
    // X = 1
    let x: Int
    // y = 1
    let y: Int

    func surroundingPoints(withRange range: Int = 1) -> [Point] {
        var results: [Point] = []
        for xCoord in (x-range)...(x+range) {
            for yCoord in (y-range)...(y+range) {
                let coordinatePoint = Point(x: xCoord, y: yCoord)
                results.append(coordinatePoint)
                print(coordinatePoint)
            }
        }
        return results
    }
}

// Creating an instance and assigning to a constant called coordinatePoint

let coordinatePoint = Point(x: 1, y: 1)
print(coordinatePoint)

// Calling the function inside Point instance
coordinatePoint.surroundingPoints()
print(coordinatePoint)

Shouldn't 

let coordinatePoint = Point(x: xCoord, y: yCoord)

be a var instead of a let? As it's changing it's value each time around the for loop? or is it created and destroyed each time?

Upvotes: 2

Views: 109

Answers (4)

Marc Khadpe
Marc Khadpe

Reputation: 2002

No. coordinatePoint is created and then destroyed once for each iteration of the for loop. (Its scope is limited to the for loop it is declared inside.) This is just like how a local variable in a function will be created and destroyed once each time you invoke the function. If you wanted to use a var instead of a let, then you would declare it outside the scope of the for loop as follows:

func surroundingPoints(withRange range: Int = 1) -> [Point] {
    var results: [Point] = []
    var coordinatePoint: Point
    for xCoord in (x-range)...(x+range) {
        for yCoord in (y-range)...(y+range) {
            coordinatePoint = Point(x: xCoord, y: yCoord)
            results.append(coordinatePoint)
            print(coordinatePoint)
        }
    }
    return results
}

Now coordinatePoint is created only once per invocation of the method. There's no particular advantage to doing so however, and using a let is probably preferable from a stylistic point of view.

Upvotes: 1

Chris DiMartino
Chris DiMartino

Reputation: 11

No - coordinatePoint inside the loop is locally scoped to that inner loop. It ceases to exist directly after the print and is recreated on the next iteration.

Upvotes: 1

vien vu
vien vu

Reputation: 4337

let or var, it depends on scope of you will use it. If you want change value after use in the same scope, you have to use var. If not you will use let. When you run this scope it will create and end scope it will be destroyed.

Upvotes: 0

Daniel Centore
Daniel Centore

Reputation: 3349

The variable is created and destroyed each time, so either would work just fine. It would be a different story if you had defined coordinatePoint above the for loop. In this case, you would have to use var.

Upvotes: 4

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