NIOAny

public struct NIOAny

NIOAny is an opaque container for values of any type, similar to Swift’s builtin Any type. Contrary to Any the overhead of NIOAny depends on the the type of the wrapped value. Certain types that are important for the performance of a SwiftNIO application like ByteBuffer, FileRegion and AddressEnvelope<ByteBuffer> can be expected to be wrapped almost without overhead. All others will have similar performance as if they were passed as an Any as NIOAny just like Any will contain them within an existential container.

The most important use-cases for NIOAny are values travelling through the ChannelPipeline whose type can’t be calculated at compile time. For example:

• the channelRead of any ChannelInboundHandler
• the write method of a ChannelOutboundHandler

The abstraction that delivers a NIOAny to user code must provide a mechanism to unwrap a NIOAny as a certain type known at run-time. Canonical example:

class SandwichHandler: ChannelInboundHandler {
    typealias InboundIn = Bacon /* we expected to be delivered `Bacon` ... */
    typealias InboundOut = Sandwich /* ... and we will make and deliver a `Sandwich` from that */

    func channelRead(ctx: ChannelHandlerContext, data: NIOAny) {
         /* we receive the `Bacon` as a `NIOAny` as at compile-time the exact configuration of the channel
            pipeline can't be computed. The pipeline can't be computed at compile time as it can change
            dynamically at run-time. Yet, we assert that in any configuration the channel handler before
            `SandwichHandler` does actually send us a stream of `Bacon`.
         */
         let bacon = self.unwrapInboundIn(data) /* `Bacon` or crash */
         let sandwich = makeSandwich(bacon)
         ctx.fireChannelRead(self.wrapInboundOut(sandwich)) /* as promised we deliver a wrapped `Sandwich` */
    }
}