Default parameter values in Swift - Step-by-Step Execution

Concept Flow - Default parameter values

Function call

↓

Check if argument provided?

No→Use default value

Yes↓

Use provided argument

↓

Execute function body with argument

↓

Return result or complete

When calling a function, Swift checks if an argument is given. If not, it uses the default value. Then it runs the function with that value.

Execution Sample

Swift

func greet(name: String = "Friend") {
    print("Hello, \(name)!")
}

greet()
greet(name: "Anna")

This code defines a function with a default name. It prints a greeting using the default or given name.

Execution Table

Step	Function Call	Argument Provided?	Parameter Value Used	Output
1	greet()	No	"Friend"	Hello, Friend!
2	greet(name: "Anna")	Yes	"Anna"	Hello, Anna!
3	End	-	-	No more calls

💡 No more function calls, execution ends.

Variable Tracker

Variable	Start	After Call 1	After Call 2	Final
name	-	"Friend"	"Anna"	-

Key Moments - 2 Insights

Why does greet() print "Hello, Friend!" even though no argument is given?

Because the function has a default value "Friend" for the parameter 'name', it uses this when no argument is provided (see execution_table row 1).

What happens if we provide an argument like greet(name: "Anna")?

The function uses the provided argument "Anna" instead of the default (see execution_table row 2), so it prints "Hello, Anna!".

Visual Quiz - 3 Questions

Look at the execution table, what is the parameter value used when greet() is called without arguments?

A "Friend"

B "Anna"

C nil

D Empty string

💡 Hint

Check execution_table row 1 under 'Parameter Value Used'

At which step does the function use the provided argument instead of the default?

A Step 1

B Step 3

C Step 2

D None

💡 Hint

Look at execution_table row 2 'Argument Provided?' column

If we remove the default value from the function, what will happen when calling greet() without arguments?

A It will print "Hello, Friend!"

B It will cause a compile error

C It will print "Hello, !"

D It will use nil as the name

💡 Hint

Default values allow calls without arguments; removing it requires argument (see concept_snapshot)

Concept Snapshot

func functionName(parameter: Type = defaultValue) {
  // function body
}

- If argument is missing, defaultValue is used.
- If argument is given, it overrides default.
- Helps avoid writing multiple function versions.

Full Transcript

This visual shows how Swift functions use default parameter values. When you call a function without giving an argument, Swift uses the default value you set. If you provide an argument, it uses that instead. The example greet() prints a greeting using the default name "Friend" if no name is given, or the provided name otherwise. The execution table traces each call, showing the parameter value used and the output. The variable tracker shows how the 'name' parameter changes with each call. Key moments clarify why default values matter and how they work. The quiz tests understanding by asking about parameter values and behavior when defaults are removed.