Add higher-order types (Kinds) - #351
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| attr_reader :type | ||
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| def ===(object) | ||
| Literal.subtype?(object, @type) |
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KindType#=== currently relies on Literal.subtype?(object, @type), but module-based subtyping only succeeds for a small subset of literal wrapper types (ConstraintType, IntersectionType, UnionType, NeverType). As a result, _Kind(Array) rejects _Array(Integer) (and similarly for other wrappers like _Hash), even though those types are semantically constrained to arrays. This makes higher-order constraints unexpectedly fail for common generic type arguments.
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No it doesn't. Look at the implementation of Literal.subtype?
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Added a
_Kindgeneric to create higher-order types (kinds). This type constructor takes a type and return the type of its type. In other words, it will match the type itself or any subtype of that type.This is useful in situations where you want to take a type as an argument and you want to constrain what kinds of types are allowed.
_Kindworks for complex types tooIf you want to compose one kind into another, you can lift it with
type.I am using this to create operation classes where parameters must be only serialisable types. It means we can know at boot time rather than runtime that all types on the operations can only match objects that can be serialized / deserialized.