Data structure that can hold either the totality or a subset of a larger piece of data.

This can be used to reconcile bits of data that are coming from several locations, or to send a piece of data towards different locations.

For instance :

structure AB {
  @httpPayload
  @required
  a: String,

  @httpHeader("X-B")
  @required
  b: String
}

translates to this case class

case class AB(a: String, b: String)

.

However, codec derivation (performed by the SchemaVisitor mechanism in Smithy4s), does not let us easily solve for problem such as http message decoding, because of the notion of priority : the http body of a message should not be decoded if the metadata is not fully decoded first.

In order to solve for this, the PartialData type allows to momentarily store a subset of the fields of a case class so that it can be reconciled with other pieces of PartialData later on.