# TryCapture A regex component that attempts to transform a matched substring, saving the result if successful and backtracking if the transformation fails. ``` struct TryCapture

``` ## Overview You use a `TryCapture` component to capture part of a match as a transformed value, when a failure to transform should mean the regex continues matching, backtracking from that point if necessary. The code below demonstrates using `TryCapture` to include a test that the `Double` value of a capture is over a limit. In the example, `regex` matches a dollar sign (`"$"`) followed by one or more digits, a period (`"."`), and then two additional digits, as long as that pattern appears at the end of the line. The `TryCapture` block wraps the digits and period, capturing that part of the match separately and passing it to its `transform` closure. That closure converts the captured portion of the match, converts it to a `Double`, and only returns a non-`nil` value if it is over the transaction limit. ``` let transactions = """ CREDIT 109912311421 Payroll $69.73 CREDIT 105912031123 Travel $121.54 DEBIT 107733291022 Refund $8.42 """ let transactionLimit = 100.0 let regex = Regex { "$" TryCapture { OneOrMore(.digit) "." Repeat(.digit, count: 2) } transform: { str -> Double? in let value = Double(str)! if value > transactionLimit { return value } return nil } Anchor.endOfLine } ``` When the `TryCapture` block’s `transform` closure processes the three different amounts in the list of transactions, it only returns a non-`nil` value for the $121.54 transaction. Even though the capture returns an optional `Double` value, the captured value is non-optional. ``` // The type of each match's output is `(Substring, Double)`. for match in transactions.matches(of: regex) { print("Transaction amount: \(match.1)") } // Prints "Transaction amount: 121.54" ``` Throwing an error from a `transform` closure aborts matching and propagates the error out to the caller. If you want to capture the `nil` results of a failable transformation, instead of continuing a search, use [`Capture`](/documentation/RegexBuilder/Capture) instead of `TryCapture`. ## Topics ### Initializers [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-2a4o2) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-2bjbf) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-41r67) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-4kzw6) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-674ml) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-7tqt7) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-88lf1) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-89xrg) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-8m89r) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-9p9ig) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(some RegexComponent, as: Reference, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:as:transform:)-z449) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-18te8) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-1oiex) Creates a capture for the given component, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-1q8tj) Creates a capture for the given component, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-2akes) Creates a capture for the given component, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-2cmjm) Creates a capture for the given component, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-2o3dd) Creates a capture for the given component, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-35erc) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-49jj) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-4ctec) Creates a capture for the given component, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-4fb8m) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-55y26) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-5blap) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-5f28q) Creates a capture for the given component, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-5qk0r) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-631wm) Creates a capture for the given component, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-7vgez) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-7w4kc) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-8d6xo) Creates a capture for the given component, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-8kgfm) Creates a capture for the given component, attempting to transform with the given closure. [`init(() -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-951zx) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-9oonc) Creates a capture for the given component, attempting to transform with the given closure. [`init(some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(_:transform:)-t0lx) Creates a capture for the given component, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-2nfnn) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-5tqfd) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-6vy4m) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-7di2q) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-7j2mj) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-7pe1b) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-85qkx) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-8byjf) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-8xl17) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-b8x0) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. [`init(as: Reference, () -> some RegexComponent, transform: (W) throws -> NewCapture?)`](/documentation/RegexBuilder/TryCapture/init(as:_:transform:)-p58t) Creates a capture for the given component using the specified reference, attempting to transform with the given closure. ## Relationships ### Conforms To [`RegexComponent`](/documentation/Swift/RegexComponent) [`Copyable`](/documentation/Swift/Copyable) [`Escapable`](/documentation/Swift/Escapable) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)