Is operator for type checking in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if variable 'item' is of type String.

Swift

if item [1] String {
    print("It's a string")
}

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

A==

Bas

Cis

Dinstanceof

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'as' instead of 'is' for type checking.

The is operator checks if a variable is of a certain type in Swift.

2fill in blank

medium

Complete the code to check if 'value' is an Int before casting.

Swift

if value [1] Int {
    let number = value as! Int
    print(number)
}

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

Ais

Bas

C==

Dinstanceof

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'as' instead of 'is' for checking type.

Use is to check type before force casting with as!.

3fill in blank

hard

Fix the error in the code to check if 'obj' is a Double.

Swift

if obj [1] Double {
    print("Double value")
}

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

Ais

Binstanceof

C==

Das

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'as' instead of 'is' causes a compile error.

The is operator is used for type checking in Swift, not as.

4fill in blank

hard

Fill both blanks to check if 'element' is a String and then cast it safely.

Swift

if element [1] String {
    if let str = element [2] String {
        print(str)
    }
}

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

Ais

Bas?

Cas!

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'as!' for casting without checking type first.

Use is to check type and as? for safe casting.

5fill in blank

hard

Fill all three blanks to check if 'data' is an Int, cast it safely, and print it.

Swift

if data [1] Int {
    if let number = data [2] Int {
        print(number [3] 10)
    }
}

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

Ais

Bas?

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'as!' without checking type, or using wrong operator for addition.

Check type with is, safely cast with as?, then add 10 with +.

Practice

1. What does the is operator do in Swift?

easy

A. Checks if a value is of a certain type

B. Converts a value to another type

C. Declares a new variable

D. Compares two values for equality

Solution

1. Step 1: Understand the purpose of is operator

   The is operator is used to check the type of a value in Swift.

2. Step 2: Differentiate from other operators

   Unlike conversion or comparison, is only checks type and returns true or false.

3. Final Answer:

   Checks if a value is of a certain type -> Option A

4. Quick Check:

   is operator = type check [OK]

Hint: Remember: is checks type, not value or conversion [OK]

Common Mistakes:

• Confusing is with type casting
• Thinking is compares values
• Using is to convert types

2. Which of the following is the correct syntax to check if variable item is of type String in Swift?

easy

A. if item == String { }

B. if item as String { }

C. if item is String { }

D. if item instanceof String { }

Solution

1. Step 1: Recall Swift type checking syntax

   Swift uses is to check type, so item is String is correct.

2. Step 2: Identify incorrect options

   == compares values, as is for casting, and instanceof is not Swift syntax.

3. Final Answer:

   if item is String { } -> Option C

4. Quick Check:

   Type check syntax = is [OK]

Hint: Use is for type checks, not as or == [OK]

Common Mistakes:

• Using == instead of is
• Confusing is with as
• Using JavaScript's instanceof in Swift

3. What will be the output of the following Swift code?

let value: Any = 42
if value is Int {
    print("Integer")
} else {
    print("Not an Integer")
}

medium

A. Runtime error

B. Not an Integer

C. Compilation error

D. Integer

Solution

1. Step 1: Analyze the variable type

   The variable value is declared as Any but holds the integer 42.

2. Step 2: Check the is condition

   The condition value is Int checks if the value is an integer, which is true.

3. Final Answer:

   Integer -> Option D

4. Quick Check:

   is Int on 42 = true [OK]

Hint: Check actual stored type, not declared type [OK]

Common Mistakes:

• Assuming Any means not Int
• Expecting a compile error for is
• Confusing is with casting

4. Identify the error in the following Swift code snippet:

let obj: Any = "Hello"
if obj is String {
    print(obj as String)
}

medium

A. Incorrect casting syntax with as

B. Using is instead of as?

C. Missing optional binding for safe cast

D. No error, code runs correctly

Solution

1. Step 1: Understand casting syntax in Swift

   Direct casting with as requires the compiler to know the type; here obj is Any.

2. Step 2: Identify the correct cast usage

   Safe cast should use as? with optional binding or forced cast as!. Using as String alone causes error.

3. Final Answer:

   Incorrect casting syntax with as -> Option A

4. Quick Check:

   Use as? or as! for casting [OK]

Hint: Use as? for safe cast, not plain as [OK]

Common Mistakes:

• Using as without optional binding
• Ignoring safe cast with as?
• Assuming is casts automatically

5. Given a list of mixed types: let items: [Any] = [1, "two", 3.0, "four"], which Swift code correctly prints only the strings using the is operator?

hard

A. for item in items { if item == String { print(item) } }

B. for item in items { if item is String { print(item) } }

C. for item in items { if item as String { print(item) } }

D. for item in items { if item instanceof String { print(item) } }

Solution

1. Step 1: Understand the goal

   We want to print only elements that are strings from a mixed array.

2. Step 2: Use correct type check syntax

   The is operator checks type correctly; item is String returns true for strings.

3. Step 3: Identify incorrect options

   == String compares values, as String is invalid syntax here, and instanceof is not Swift.

4. Final Answer:

   for item in items { if item is String { print(item) } } -> Option B

5. Quick Check:

   Use is to filter by type [OK]

Hint: Loop and check type with is to filter items [OK]

Common Mistakes:

• Using equality instead of type check
• Trying to cast inside condition incorrectly
• Using non-Swift keywords like instanceof