我在数组文档中发现了同样的新行。看起来只有当参数是块时才有效。这里是来自苹果的示例

/// - Parameters:
    ///   - unsafeUninitializedCapacity: The number of elements to allocate
    ///     space for in the new array.
    ///   - initializer: A closure that initializes elements and sets the count
    ///     of the new array.
    ///     - Parameters:
    ///       - buffer: A buffer covering uninitialized memory with room for the
    ///         specified number of elements.
    ///       - initializedCount: The count of initialized elements in the array,
    ///         which begins as zero. Set `initializedCount` to the number of
    ///         elements you initialize.
    @inlinable public init(unsafeUninitializedCapacity: Int, initializingWith initializer: (_ buffer: inout UnsafeMutableBufferPointer<Element>, _ initializedCount: inout Int) throws -> Void) rethrows

链接到开源的corelib，具有相同的注解