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Subtypes

In Rell, the concept of subtypes enhances code flexibility and reusability by allowing seamless assignment between compatible types.

If type B is a subtype of type A, you can freely assign a value of type B to a variable of type A or pass it as an argument to a function expecting type A.

Common subtype relationships​

  • Optional types:

    • T is a subtype of T? (a non-nullable type is a subtype of its nullable counterpart).
    • null is a subtype of T? (null can be assigned to any nullable type).

  • Tuples:

    • (T, P) is a subtype of (T?, P?), (T?, P), and (T, P?) (tuples with more specific types are subtypes of tuples with more general types).