[Solved] What is the output of this Swift code? var scores = ["Alice": 10, "Bob": 8] let oldValue = scores.updateValue(12, forKey: "Alice") let missingValue = scores.... What is the output of this Swift code? | Swift

Swift - Collections

What is the output of this Swift code?

var scores = ["Alice": 10, "Bob": 8]
let oldValue = scores.updateValue(12, forKey: "Alice")
let missingValue = scores.updateValue(5, forKey: "Charlie")
print(oldValue, missingValue, scores)

Anil Optional(5) ["Alice": 12, "Bob": 8, "Charlie": 5]

B10 5 ["Alice": 12, "Bob": 8, "Charlie": 5]

COptional(10) nil ["Alice": 12, "Bob": 8, "Charlie": 5]

DOptional(12) Optional(5) ["Alice": 10, "Bob": 8, "Charlie": 5]

Step-by-Step Solution

Solution:

Step 1: Understand updateValue return values
Updating "Alice" from 10 to 12 returns old value Optional(10). Adding "Charlie" returns nil because key was missing.
Step 2: Check dictionary after updates
Dictionary now has "Alice":12, "Bob":8, and "Charlie":5.
Final Answer:
Optional(10) nil ["Alice": 12, "Bob": 8, "Charlie": 5] -> Option C
Quick Check:
updateValue returns old value or nil [OK]

Quick Trick: updateValue returns old value wrapped in Optional or nil if new key [OK]

Common Mistakes:

Expecting updateValue to return new value
Forgetting Optional wrapping
Not updating dictionary correctly

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What is the output of this Swift code?

Step 1: Understand updateValue return values

Step 2: Check dictionary after updates

Final Answer:

Quick Check:

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