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Remove all other methods, and restrict RFC to just including hassubtypeof

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gaymeowing 2025-03-06 07:57:55 -05:00
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docs/user-side-subtype-checking-methods.md → docs/method-type-hassubtypeof.md
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@ -1,8 +1,8 @@
# Subtype Checking methods for User-Defined Type Functions
# type:hassubtypeof
## Summary
New methods on the `type` userdata in type functions for performing subtype checks.
New method on the [`type`](./user-defined-type-functions.md#type-instance) userdata in type functions for performing subtype checks.
## Motivation
@ -99,64 +99,15 @@ end
## Design
This RFC proposes adding 4 new methods to the [`type`](./user-defined-type-functions.md#type-instance) userdata in type functions.
The [`type`](./user-defined-type-functions.md#type-instance) will gain a new method: `hassubtypeof`:
### New Methods
| Name | Return Type | Description |
| ------------- | ------------- | ------------- |
| `hassubtype(arg: string)` | `boolean` | returns true if self has a subtype of the same tag as the argument. List of available tags: "nil", "unknown", "never", "any", "boolean", "number", "string", "singleton", "negation", "union", "intersection", "table", "function", "class" |
| `hassubtypeof(arg: type)` | `boolean` | returns true if self has a subtype of the argument. |
| `musthavesubtype(arg: string)` | `boolean` | returns true if self has only a subtype of the same tag as the argument. List of available tags: "nil", "unknown", "never", "any", "boolean", "number", "string", "singleton", "negation", "union", "intersection", "table", "function", "class" |
| `musthavesubtypeof(arg: type)` | `boolean` | returns true if self has a subtype of the argument. |
The `musthave` methods are diffrent with how they validate, as shown below.
### String Enum Examples
```luau
type meow = number | "mrrp" | string
print(meow:musthavesubtypeof(types.string)) -- false, because theres a number in the union.
print(meow:hassubtypeof(types.string)) -- true, because even though theres a number, theres also types with a subtype of string, and also string itself.
type mrow = "purr" | "meow"
print(meow:musthavesubtypeof(types.string)) -- true, because despite the union being made up of singletons. Those singletons have the subtype of string, so it returns true.
print(meow:hassubtypeof(types.string)) -- true
```
### Tagged Enum Examples
```luau
type CatnipPurity = "90%" | "10%" | "11%"
type BaseCatnipInfo<P = CatnipPurity> = {
purity: P
}
type TwentyPercentPurityCatnip = {
purity: "20%"
name: "Average Catnip"
}
print(TwentyPercentPurityCatnip:musthavesubtypeof(BaseCatnipInfo)) -- false, because "20%" is not an option in the string enum 'CatnipPurity'.
print(TwentyPercentPurityCatnip:hassubtypeof(BaseCatnipInfo)) -- also false for the same reason
type WeakCatnip = BaseCatnipInfo<"10%"> & {
name: "Weak Catnip"
}
print(WeakCatnip:musthavesubtypeof(BaseCatnipInfo)) -- true, because unlike the previous example "10%" is an option in the string enum 'CatnipPurity'.
print(TwentyPercentPurityCatnip:hassubtypeof(BaseCatnipInfo)) -- also true
type FishyCatnipUnion = WeakCatnip | TwentyPercentPurityCatnip
print(FishyCatnipUnion:musthavesubtypeof(BaseCatnipInfo)) -- false, because "20%" is not an option in the string enum 'CatnipPurity'.
print(TwentyPercentPurityCatnip:hassubtypeof(BaseCatnipInfo)) -- true, because atleast one of the components has the subtype of BaseCatnipInfo (WeakCatnip).
type:hassubtypeof(arg: type): boolean
```
## Drawbacks
Adds extra methods to the type userdata in User-Defined type functions.
Adds another method to the type userdata in User-Defined type functions.
## Alternatives