# AlternationBuilder A custom parameter attribute that constructs regular expression alternations from closures. ``` @resultBuilder struct AlternationBuilder ``` ## Overview When you use a `ChoiceOf` initializer, the initializer’s closure parameter has an `AlternationBuilder` attribute, allowing you to provide multiple regular expression statements as alternatives. ## Topics ### Type Methods [`static func buildExpression(R) -> R`](/documentation/RegexBuilder/AlternationBuilder/buildExpression(_:)) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5?, C6?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-1jq94) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-1oadq) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6?, C7?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-1vk92) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7, C8)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-20ao) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-28nze) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7, C8, C9, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-2afed) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1?, C2?, C3?, C4?, C5?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-2q3in) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2?, C3?, C4?, C5?, C6?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-2yatq) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5?, C6?, C7?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-30m9e) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1?, C2?, C3?, C4?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-3571v) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-38zc3) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1?, C2?, C3?, C4?, C5?, C6?, C7?, C8?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-39yml) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3?, C4?, C5?, C6?, C7?, C8?, C9?, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-3a1qj) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2?, C3?, C4?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-3ascd) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3?, C4?, C5?, C6?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-3b47j) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-3eldc) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4?, C5?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-3ibe4) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7, C8?, C9?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-3nzbh) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4?, C5?, C6?, C7?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-3rkqj) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3?, C4?, C5?, C6?, C7?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-3wkc9) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-42jgz) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-46i6m) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5?, C6?, C7?, C8?, C9?, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-4jwp3) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3?, C4?, C5?, C6?, C7?, C8?, C9?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-4nz0t) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2?, C3?, C4?, C5?, C6?, C7?, C8?, C9?, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-4q1xd) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-53xav) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6?, C7?, C8?, C9?, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-576fa) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3?, C4?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-57987) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7?, C8?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-5afat) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7, C8?, C9?, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-5fcrr) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1?, C2?, C3?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-5me97) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6?, C7?, C8?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-5qva) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-5wwt0) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6074o) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4?, C5?, C6?, C7?, C8?, C9?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-653ta) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4?, C5?, C6?, C7?, C8?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6842g) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2?, C3?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6anqe) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6hkv5) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7, C8, C9)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6nfpu) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3?, C4?, C5?, C6?, C7?, C8?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6pfu4) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1?, C2?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6tz5g) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1?, C2?, C3?, C4?, C5?, C6?, C7?, C8?, C9?, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6vjm9) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6vp0) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5?, C6?, C7?, C8?, C9?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6x6gg) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1?, C2?, C3?, C4?, C5?, C6?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-6yu9n) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7, C8, C9?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-70usl) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6?, C7?, C8?, C9?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-71zj2) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2?, C3?, C4?, C5?, C6?, C7?, C8?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-7ihw4) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4?, C5?, C6?, C7?, C8?, C9?, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-7jsg7) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-815py) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4?, C5?, C6?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-8a7vx) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2?, C3?, C4?, C5?, C6?, C7?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-8dd0v) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2?, C3?, C4?, C5?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-8e0ap) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-8pz3c) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-90yht) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-9f39x) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7?, C8?, C9?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-9g62e) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5?, C6?, C7?, C8?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-9k7s0) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7, C8?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-9op0h) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3?, C4?, C5?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-9s1co) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7?, C8?, C9?, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-b6ks) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1?, C2?, C3?, C4?, C5?, C6?, C7?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-klfl) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2, C3, C4, C5, C6, C7, C8, C9?, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-o7ny) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1?, C2?, C3?, C4?, C5?, C6?, C7?, C8?, C9?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-q4oo) [`static func buildPartialBlock(accumulated: some RegexComponent, next: some RegexComponent) -> ChoiceOf<(Substring, C1, C2?, C3?, C4?, C5?, C6?, C7?, C8?, C9?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(accumulated:next:)-toh7) [`static func buildPartialBlock(first: R) -> ChoiceOf<(W, C1?, C2?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-1kh7h) [`static func buildPartialBlock(first: R) -> ChoiceOf<(W, C1?, C2?, C3?, C4?, C5?, C6?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-271vl) [`static func buildPartialBlock(first: R) -> ChoiceOf<(W, C1?, C2?, C3?, C4?, C5?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-3f6z3) [`static func buildPartialBlock(first: R) -> ChoiceOf<(W, C1?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-520tx) [`static func buildPartialBlock(first: R) -> ChoiceOf<(W, C1?, C2?, C3?, C4?, C5?, C6?, C7?, C8?, C9?, C10?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-5qbok) [`static func buildPartialBlock(first: R) -> ChoiceOf<(W, C1?, C2?, C3?, C4?, C5?, C6?, C7?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-63ah5) [`static func buildPartialBlock(first: R) -> ChoiceOf<(W, C1?, C2?, C3?, C4?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-6mjz0) [`static func buildPartialBlock(first: R) -> ChoiceOf<(W, C1?, C2?, C3?, C4?, C5?, C6?, C7?, C8?, C9?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-6vt65) [`static func buildPartialBlock(first: R) -> ChoiceOf`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-7jdle) [`static func buildPartialBlock(first: R) -> ChoiceOf<(W, C1?, C2?, C3?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-c2a6) [`static func buildPartialBlock(first: R) -> ChoiceOf<(W, C1?, C2?, C3?, C4?, C5?, C6?, C7?, C8?)>`](/documentation/RegexBuilder/AlternationBuilder/buildPartialBlock(first:)-uy7q) --- Copyright © 2026 Apple Inc. 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