[Solved] The following Swift code tries to modify a property of a struct instance inside a function but causes a compile error:struct Counter { var count: Int } func increment(counter: Counter) { counter.... | iOS Swift

iOS Swift - Swift Language Essentials

The following Swift code tries to modify a property of a struct instance inside a function but causes a compile error:

struct Counter {
  var count: Int
}

func increment(counter: Counter) {
  counter.count += 1
}

What is the main reason for the error?

AFunction parameter 'counter' is a constant by default

BStruct properties cannot be modified inside functions

CYou cannot use '+=' operator on Int

DCounter must be a class to modify properties

Step-by-Step Solution

Solution:

Step 1: Understand function parameter mutability
In Swift, function parameters are constants by default. You cannot modify them inside the function.
Step 2: Analyze the error cause
The parameter counter is a struct instance passed by value but immutable inside the function. Trying to change counter.count causes a compile error.
Final Answer:
Function parameter 'counter' is a constant by default -> Option A
Quick Check:
Function parameters are immutable unless marked inout [OK]

Quick Trick: Function parameters are constants unless 'inout' is used [OK]

Common Mistakes:

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The following Swift code tries to modify a property of a struct instance inside a function but causes a compile error: