Closure Shorthand Syntax
Closure shorthand is Swift's way of letting you write a closure with fewer words once the context already makes things obvious.
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Syntax
array.sorted { a, b in a < b } // inferred types, implicit return
array.map { $0 * 2 } // shorthand names $0, $1
array.sorted(by: >) // operator as closureType Inference and Implicit Return
When Swift already knows a closure's expected type from context, the closure can drop explicit types and the return keyword for a single expression.
Example: Type Inference and Implicit Return
// Declare a constant `numbers`, set to `[4, 2, 7, 1]`
let numbers = [4, 2, 7, 1]
// Declare a constant `sorted`, set to `numbers.sorted { a, b in a < b }`
let sorted = numbers.sorted { a, b in a < b }
// Print `sorted` to the console
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Shorthand Argument Names
Swift automatically provides $0, $1, etc. as names for a closure's parameters, letting you skip naming them entirely for short closures.
Example: Shorthand Argument Names
// Declare a constant `numbers`, set to `[4, 2, 7, 1]`
let numbers = [4, 2, 7, 1]
// Declare a constant `doubled`, set to `numbers.map { $0 * 2 }`
let doubled = numbers.map { $0 * 2 }
// Declare a constant `sorted`, set to `numbers.sorted { $0 < $1 }`
let sorted = numbers.sorted { $0 < $1 }
// Print `doubled` to the console
print(doubled)
// Print `sorted` to the console
print(sorted)Login to try C/C++/Java/PHP code in the editor
Passing an Operator as a Closure
When an operator's signature matches the expected closure type exactly, it can be passed directly by name instead of writing out a closure.
Example: Passing an Operator as a Closure
// Declare a constant `numbers`, set to `[4, 2, 7, 1]`
let numbers = [4, 2, 7, 1]
// Declare a constant `descending`, set to `numbers.sorted(by: >)`
let descending = numbers.sorted(by: >)
// Print `descending` to the console
print(descending)Login to try C/C++/Java/PHP code in the editor
Related Topics
{# common_mistakes/chapter_summary/browser_support: on Hindi pages the
view already swaps in the hi_ translation fields (or blanks these
out if untranslated), so this renders correctly for both languages
without a lang_code check here. #}
Common Mistakes
- Overusing
$0,$1shorthand for closures with complex logic, hurting readability; shorthand is best for short, simple closures. - Writing
returnin a single-expression closure body; it's implicit and optional there but required in multi-statement closures. - Forgetting operator functions like
+or>can be passed directly as a closure when their signature matches exactly.
Chapter Summary
- Swift can infer parameter and return types in a closure passed to a known function signature.
$0,$1, etc. refer to a closure's parameters positionally without naming them.- A single-expression closure body can omit the
returnkeyword. - Operators like
+,<, or>can be passed directly as closures matching a two-parameter function type.
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