Improving Code Quality - Session 47: Breach of non-performance

This covers the risks that can occur when implementing a Null Object using Kotlin's default parameter.

Setting a value with special meaning, such as id = 0, as a default parameter creates the risk that an 'invalid object' may be unintentionally created when a developer mistakenly omits a specific argument. This problem arises because the default value represents a special state rather than a general value.

Alternatives for a safer design are as follows:

• Define an explicit instance such as INVALID through a companion object.
• Clearly distinguish between Valid and Invalid using a sum type leveraging a sealed interface.
• Use a nullable type to represent the invalid state with null.

In conclusion, default parameters should use general values that anyone can predict, rather than values with a special purpose.