Mutating methods for value types in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a mutating method that changes the value of a property.

Swift

struct Counter {
    var count = 0
    mutating func increment() {
        count [1] 1
    }
}

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A+=

B-=

C*=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' to increment.

Not marking the method as mutating.

The increment method adds 1 to count using the += operator. This requires the method to be mutating because it changes the struct's property.

2fill in blank

medium

Complete the code to mark the method as mutating so it can modify the struct's property.

Swift

struct Point {
    var x = 0, y = 0
    [1] func moveBy(x deltaX: Int, y deltaY: Int) {
        x += deltaX
        y += deltaY
    }
}

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Astatic

Bmutating

Cfinal

Doverride

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'static' which means the method belongs to the type, not instance.

Forgetting to mark the method as mutating.

The mutating keyword allows the method to change properties of the struct. Without it, the method cannot modify x and y.

3fill in blank

hard

Fix the error in the mutating method that tries to assign a new value to self.

Swift

struct Rectangle {
    var width: Int
    var height: Int
    mutating func doubleSize() {
        self [1] Rectangle(width: width * 2, height: height * 2)
    }
}

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A-=

B==

C=

D+=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '=' causes a syntax error.

Trying to modify properties without marking the method as mutating.

Assigning a new value to self inside a mutating method requires the assignment operator =. Using == is a comparison and causes an error.

4fill in blank

hard

Fill both blanks to create a mutating method that resets the point to origin.

Swift

struct Point {
    var x: Int
    var y: Int
    [1] func reset() {
        x [2] 0
        y = 0
    }
}

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Amutating

Bstatic

C+=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Not marking the method as mutating.

Using '+=' instead of '=' to reset the value.

The method must be marked mutating to change properties. To reset x, use the assignment operator = to set it to 0.

5fill in blank

hard

Fill all three blanks to create a mutating method that scales the size and updates the description.

Swift

struct Size {
    var width: Int
    var height: Int
    var description: String
    [1] func scale(by factor: Int) {
        width [2] width * factor
        height [3] height * factor
        description = "Scaled size"
    }
}

Drag options to blanks, or click blank then click option'

Amutating

B=

C+=

D*=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*=' instead of '=' causes incorrect scaling logic here.

Not marking the method as mutating.

The method must be mutating to change properties. To update width and height, assign the new scaled values using =. The description is updated by assignment.