Argument labels and parameter names in Swift - Step-by-Step Execution

Concept Flow - Argument labels and parameter names

Define function with labels and names

↓

Call function with argument labels

↓

Match labels to parameters

↓

Execute function body using parameter names

↓

Return or print result

↓

End

This flow shows how Swift uses argument labels in calls to match parameters in function definitions, then runs the function body.

Execution Sample

Swift

func greet(person name: String, from hometown: String) {
    print("Hello \(name)! Glad you could visit from \(hometown).")
}
greet(person: "Anna", from: "Paris")

Defines a function with argument labels and parameter names, then calls it with matching labels.

Execution Table

Step	Action	Argument Label	Parameter Name	Value	Output
1	Define function	-	person (name), from (hometown)	-	-
2	Call function	person	name	"Anna"	-
3	Call function	from	hometown	"Paris"	-
4	Execute print	-	-	-	Hello Anna! Glad you could visit from Paris.
5	End	-	-	-	-

💡 Function completes after printing greeting message.

Variable Tracker

Variable	Start	After Call
name	-	"Anna"
hometown	-	"Paris"

Key Moments - 2 Insights

Why do we use argument labels like 'person' and 'from' instead of just parameter names?

Argument labels clarify the meaning when calling the function, as shown in execution_table rows 2 and 3 where labels 'person' and 'from' match parameters 'name' and 'hometown'.

Can the argument label and parameter name be different?

Yes, as in the example, the label 'person' corresponds to parameter 'name'. This helps make calls readable while keeping parameter names descriptive inside the function (see execution_table step 2).

Visual Quiz - 3 Questions

Look at the execution table, what value does the parameter 'name' have at step 2?

A "person"

B "Anna"

C "Paris"

D No value yet

💡 Hint

Check the 'Parameter Name' and 'Value' columns at step 2 in the execution_table.

At which step does the function print the greeting message?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the 'Output' column in the execution_table to find when the message appears.

If we swapped the argument labels in the call, what would happen?

A The function would print the same message.

B The function would print a message with swapped names.

C The code would not compile due to label mismatch.

D The function would ignore the labels and use parameter order.

💡 Hint

Swift requires argument labels to match function definition; see steps 2 and 3 in execution_table.

Concept Snapshot

Swift functions can have argument labels and parameter names.
Argument labels are used when calling the function.
Parameter names are used inside the function body.
Labels can differ from parameter names for clarity.
Calls must use correct argument labels to match parameters.

Full Transcript

This visual execution shows how Swift uses argument labels and parameter names in functions. First, the function is defined with labels 'person' and 'from' and parameters 'name' and 'hometown'. When calling the function, the argument labels 'person' and 'from' are used to pass values 'Anna' and 'Paris'. The function matches these labels to parameters and executes the print statement using parameter names. The output is the greeting message. This helps make function calls clear and readable while keeping parameter names descriptive inside the function.