Genericised @_functionBuilder that appends to mutable collections

CollectionBuilder.swift

@_functionBuilder
public enum CollectionBuilder<Element>: SimpleBuilder {
    public typealias Component = Element
}

public extension RangeReplaceableCollection {
    mutating func collect (@CollectionBuilder<Element> _ builder: () -> Element) {
        append(builder())
    }

    mutating func collect (@CollectionBuilder<Element> _ builder: () -> [Element]) {
        append(contentsOf: builder())
    }
}

public extension Set {
    mutating func collect(@CollectionBuilder<Element> _ builder: () -> Element) {
        insert(builder())
    }

    mutating func collect(@CollectionBuilder<Element> _ builder: () -> [Element]) {
        for element in builder() {
            insert(element)
        }
    }
}

SimpleBuilder.swift

public protocol SimpleBuilder {
    associatedtype Component
}

public extension SimpleBuilder {
    static func buildBlock () -> [Component] {
        []
    }

    static func buildBlock (_ child: Component) -> [Component] {
        [child]
    }

    static func buildBlock (_ children: Component...) -> [Component] {
        children
    }

    static func buildIf (_ children: Component?) -> [Component] {
        guard let children = children else {
            return []
        }
        return [children]
    }

    static func buildEither (first: Component) -> [Component] {
        [first]
    }

    static func buildEither (second: Component) -> [Component] {
        [second]
    }
}