Derivation

This page covers the ways to create Differ instances for case classes and enums (sealed traits).

Derivation for case class and enums (sealed traits)

Difflicious supports three derivation strategies for deriving instances for case class and enums (sealed traits)

• Differ.derived[T], requires Differ instances for all field types.
• Differ.derivedDeep[T] derives a Differ[T] and also automatically derives Differ instance for any field types that doesn't already have one.
• Fully automatic derivation via import difflicious.generic.auto.given will automatically re-derive a Differ instance whenever it is needed

In all derivation strategies, if there's an existing Differ instance in the implicit scope, it will be reused.

Comparison of derivation strategies

Strategy	Compile time	Allocation	Verbosity
Differ.derived[T]	Probably lowest and more predictable. It derives only T and summons the field or subtype instances already in scope.	Predictable. There's only one Differ instance for each type	High, as you need to create a Differ for each type
Differ.derivedDeep[T]	Potentially higher than derived - you may end up deriving Differ for the same type multiple times if it is used in multiple places	Better than automatic derivation. Existing instances are reused, and missing intermediate instances are generated from the explicit call site.	Medium - you can avoid defining Differ instances for all intermediate types
Fully automatic derivation	High - derivation is performed every time you request for a Differ instance	High - no Differ instance reuse unless you define them manually	Lowest - you just ask for a Differ[T] :)

Our recommendation is to start with Differ.derivedDeep, and use Differ.derived for better control. For quick experiments you can use automatic derivation, but it is not recommended for code you want to keep - The compile time drag on the codebase is generally not worth the small convenience.