Shorthand argument names ($0, $1) in Swift

Introduction

Shorthand argument names let you write shorter, simpler code when using closures. They save time by avoiding naming each argument.

When you want to quickly sort a list without writing a full closure.

When you need to transform items in a list with a simple operation.

When filtering a list based on a quick condition.

When you want to keep your code clean and easy to read for small closures.

Syntax

Swift

list.method { $0, $1 in
    // use $0 for first argument
    // use $1 for second argument
}

$0 is the first argument, $1 is the second, and so on.

You don't have to write the argument names or types explicitly.

Examples

Sorts numbers using $0 and $1 as the two items to compare.

Swift

let numbers = [3, 1, 2]
let sorted = numbers.sorted { $0 < $1 }

Transforms each name to uppercase using $0 as the current item.

Swift

let names = ["Anna", "Bob", "Cindy"]
let uppercased = names.map { $0.uppercased() }

Filters scores to keep only those 60 or above using $0 as the score.

Swift

let scores = [85, 42, 90, 75]
let passed = scores.filter { $0 >= 60 }

Sample Program

This program shows sorting, mapping, and filtering using shorthand argument names $0 and $1.

Swift

let fruits = ["apple", "banana", "cherry"]

// Sort fruits alphabetically
let sortedFruits = fruits.sorted { $0 < $1 }
print("Sorted fruits:", sortedFruits)

// Make all fruits uppercase
let upperFruits = fruits.map { $0.uppercased() }
print("Uppercase fruits:", upperFruits)

// Filter fruits that start with 'b'
let bFruits = fruits.filter { $0.hasPrefix("b") }
print("Fruits starting with 'b':", bFruits)

Important Notes

Shorthand arguments only work inside closures.

Use them for short closures to keep code clean.

For complex closures, naming arguments can improve clarity.

Summary

Shorthand argument names like $0 and $1 let you write shorter closures.

$0 is the first argument, $1 the second, and so on.

They make simple tasks like sorting, mapping, and filtering easier and cleaner.

Practice

1. What does the shorthand argument $0 represent in a Swift closure?

easy

A. The last argument passed to the closure

B. The first argument passed to the closure

C. The closure itself

D. The return value of the closure

Solution

1. Step 1: Understand shorthand argument names

   In Swift closures, $0 refers to the first argument passed to the closure.

2. Step 2: Identify $0 meaning

   Since $0 is always the first argument, it represents the first input value the closure receives.

3. Final Answer:

   The first argument passed to the closure -> Option B

4. Quick Check:

   $0 = first argument [OK]

Hint: Remember $0 is always the first input in closures [OK]

Common Mistakes:

• Confusing $0 with the return value
• Thinking $0 is the closure itself
• Mixing $0 with the last argument

2. Which of the following is the correct way to use shorthand argument names to sort an array of integers in ascending order?

easy

A. let sorted = numbers.sorted { $1 > $0 }

B. let sorted = numbers.sorted { $1 < $0 }

C. let sorted = numbers.sorted { $0 > $1 }

D. let sorted = numbers.sorted { $0 < $1 }

Solution

1. Step 1: Understand sorting with closures

   To sort ascending, the closure should return true if the first element is less than the second.

2. Step 2: Match shorthand arguments to sorting logic

   Using $0 < $1 means the first element is less than the second, which sorts ascending.

3. Final Answer:

   let sorted = numbers.sorted { $0 < $1 } -> Option D

4. Quick Check:

   Ascending sort uses $0 < $1 [OK]

Hint: Use $0 < $1 for ascending sort closures [OK]

Common Mistakes:

• Reversing $0 and $1 in comparison
• Using > instead of < for ascending
• Confusing sorting order logic

3. What is the output of the following Swift code?

let names = ["Anna", "Bob", "Charlie"]
let reversed = names.map { String($0.reversed()) }
print(reversed)

medium

A. ["annA", "boB", "eilrahc"]

B. ["Anna", "Bob", "Charlie"]

C. ["annA", "boB", "eilrahC"]

D. ["a n n A", "b o B", "c h a r l i e"]

Solution

1. Step 1: Understand the map and reversed usage

   The map applies the closure to each name. $0 is each string. $0.reversed() reverses characters.

2. Step 2: Convert reversed characters back to String

   Wrapping String($0.reversed()) creates a reversed string for each name.

3. Final Answer:

   ["annA", "boB", "eilrahC"] -> Option C

4. Quick Check:

   map + reversed string = reversed names [OK]

Hint: Remember map applies closure to each element using $0 [OK]

Common Mistakes:

• Forgetting to convert reversed characters back to String
• Expecting original array without changes
• Confusing reversed string with spaced characters

4. Identify the error in this Swift code using shorthand argument names:

let numbers = [3, 1, 2]
let sorted = numbers.sorted { $2 < $1 }
print(sorted)

medium

A. Using $2 which does not exist in this closure

B. Missing return keyword in closure

C. Incorrect array declaration syntax

D. Using sorted instead of sort method

Solution

1. Step 1: Check shorthand argument usage

   Shorthand arguments start at $0 for the first, $1 for the second. There is no $2 in a two-argument closure.

2. Step 2: Identify invalid argument index

   Using $2 causes a compile error because only $0 and $1 exist here.

3. Final Answer:

   Using $2 which does not exist in this closure -> Option A

4. Quick Check:

   Only $0 and $1 allowed in two-argument closures [OK]

Hint: Use only $0 and $1 for two-parameter closures [OK]

Common Mistakes:

• Assuming $2 exists in two-argument closures
• Forgetting shorthand argument limits
• Confusing sorted and sort method differences

5. Given the array let pairs = [(3, 5), (1, 2), (4, 4)], which closure using shorthand argument names correctly sorts the array by the sum of each tuple's elements in descending order?

hard

A. pairs.sorted { $0.0 + $0.1 > $1.0 + $1.1 }

B. pairs.sorted { $1.0 + $1.1 > $0.0 + $0.1 }

C. pairs.sorted { $0 + $1 > $1 + $0 }

D. pairs.sorted { $0.0 > $1.1 }

Solution

1. Step 1: Understand tuple access and sorting logic

   Each element is a tuple. To sort by sum descending, compare sums of $0 and $1 tuples.

2. Step 2: Check each option's correctness

   pairs.sorted { $0.0 + $0.1 > $1.0 + $1.1 } sums $0.0 + $0.1 and compares to $1.0 + $1.1 with > for descending order, which is correct.

3. Final Answer:

   pairs.sorted { $0.0 + $0.1 > $1.0 + $1.1 } -> Option A

4. Quick Check:

   Sum tuples and use > for descending sort [OK]

Hint: Sum tuple elements with $0.0 + $0.1 for sorting [OK]

Common Mistakes:

• Mixing $0 and $1 order in comparison
• Trying to add tuples directly without accessing elements
• Using incorrect tuple element indices