kotlin-sum-types

Model JSON deserialization by using sealed classes with explicit Valid and Invalid state variants. Factory create() methods parse untyped input into type-safe domain objects at system boundaries, ensuring invalid data is unrepresentable.

Parse don't validate transforms untyped external data into typed domain objects in one place. Factory create() methods with @JsonCreator enforce validation at boundaries, returning sealed Valid or Invalid states rather than scattering checks across domain logic.

Aggregate validation errors by implementing interfaces like InvalidDataClass to collect field-specific messages. This preserves original invalid values and composes nested error paths such as address.city while validating nested domain structures.

Handle controller responses by using exhaustive when statements to evaluate sealed valid and invalid types. This translates validated domain results into OK or error responses, ensuring all possible validation outcomes are explicitly covered.

Yes, this approach supports nested JSON structures by composing nested validations within sealed class hierarchies. Factory create() parsers recursively process nested input, collecting field-specific errors with composed paths like email or address.city.

Sealed classes force input to be parsed into explicit valid or invalid states at system boundaries. Unlike standard data classes, this allows domain functions to safely assume data correctness and guarantees invalid states are unrepresentable.