Providing scoped configuration

Chimney is highly configurable and has some transformer derivation rules that can be switched on/off on demand, for each specific transformation. However sometimes you may find yourself enabling (or disabling) the same flags for majority of transformations in your project. This is when you may consider using providing scoped transformer configurations.

Motivating example

Let’s consider a following example.

class Source { def field1: Int = 100 }
case class Target(field1: Int, field2: Option[String])

(new Source)
    .into[Target]
    .enableMethodAccessors
    .enableOptionDefaultsToNone
    .transform
// Target(100, None)

In order to make it working without providing any specific values, we must enable method accessors and None as Option default value.

Instead of enabling them per use-site, we can define default transformer configuration in implicit scope.

implicit val myTransformerConfig =
    TransformerConfiguration.default
        .enableMethodAccessors
        .enableOptionDefaultsToNone

(new Source)
    .into[Target]
    .transform
// Target(100, None)

(new Source).transformInto[Target]
// Target(100, None)

Then, in scope where TransformerConfiguration is available, Chimney is able to pick it up as a base configuration for transformer derivation. This way you can define your default transformers ruleset for your module or project.

Overriding scoped configuration locally

Use-site override of scoped configuration is still possible, as in the following examples.

implicit val myTransformerConfig =
    TransformerConfiguration.default
        .enableMethodAccessors
        .enableOptionDefaultsToNone

(new Source)
    .into[Target]
    .disableMethodAccessors
    .transform
// error: Chimney can't derive transformation from Source to Target
// Target
//   field1: scala.Int - no accessor named field1 in source type Source

We locally disabled previously scope-enabled method accessors, which results in compilation error. It’s expected as the local override has priority over default, scoped configuration.

implicit val myTransformerConfig =
    TransformerConfiguration.default
        .enableMethodAccessors

(new Source)
    .into[Target]
    .enableOptionDefaultsToNone
    .transform
// Target(100, None)

This way we can also enable flags partially. The final configuration is merged from scoped one and any (eventual) local one.