Unpacked outputs

By default, Smithy4s generates methods whose return type is the output structure of the corresponding operation.

For instance:

service ItemService {
  version: "1.0.0"
  operations: [GetItem]
}

operation GetItem {
  output: GetItemOutput
}

structure GetItemOutput {
    @required
    item: Item
}

structure Item {
    @required
    id: String
}

leads to something conceptually equivalent to:

trait ItemServiceGen[F[_]] {

  def getItem(): F[GetItemOutput]

}

It is however possible to annotate an operation with the smithy4s.meta#unpackedOutput trait, in order for the rendered method to return the type of the output structure's single member directly, without the wrapping case class.

For instance:

use smithy4s.meta#unpackedOutput

@unpackedOutput
operation GetItem {
  output: GetItemOutput
}

will produce the following Scala code:

trait ItemServiceGen[F[_]] {

  def getItem(): F[Item]

}

The trait can only be applied to operations whose output is a structure containing exactly one member. This is enforced by a Smithy validator; applying @unpackedOutput to an operation with a zero-member or multi-member output will fail model validation.

The wire format is unchanged by this trait: HTTP bindings (@httpPayload, @httpHeader, @httpResponseCode, etc.) applied to the single member continue to behave as if the wrapping structure were present. @unpackedOutput only affects the shape of the generated Scala method.