@swift-5.3.3
struct Box<T> {} @_functionBuilder struct MyBuilder { static func buildExpression(_ expression: Box<Never>) -> Box<Never> { expression } static func buildBlock(_ component: Box<Never>) -> Box<Never> { component } } func take(_ c: () -> Box<Never>) {} func takeBuild(@MyBuilder _ c: () -> Box<Never>) {} func test() { take { Box() } takeBuild { Box() } }