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Update typecheck.md

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Alexander McCord 2022-09-26 14:12:16 -07:00 • committed by GitHub
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@ -46,7 +46,7 @@ local a2: A = b1 -- ok
local b2: B = a1 -- not ok local b2: B = a1 -- not ok
``` ```
## Primitive types ## Builtin types
Lua VM supports 8 primitive types: `nil`, `string`, `number`, `boolean`, `table`, `function`, `thread`, and `userdata`. Of these, `table` and `function` are not represented by name, but have their dedicated syntax as covered in this [syntax document](syntax), and `userdata` is represented by [concrete types](#roblox-types); other types can be specified by their name. Lua VM supports 8 primitive types: `nil`, `string`, `number`, `boolean`, `table`, `function`, `thread`, and `userdata`. Of these, `table` and `function` are not represented by name, but have their dedicated syntax as covered in this [syntax document](syntax), and `userdata` is represented by [concrete types](#roblox-types); other types can be specified by their name.
@ -69,7 +69,7 @@ local a
local b = nil local b = nil
``` ```
## `unknown` type ### `unknown` type
`unknown` is also said to be the _top_ type, that is it's a union of all types. `unknown` is also said to be the _top_ type, that is it's a union of all types.
@ -100,7 +100,7 @@ if typeof(x) == "number" then
end end
``` ```
## `never` type ### `never` type
`never` is also said to be the _bottom_ type, meaning there doesn't exist a value that inhabits the type `never`. In fact, it is the _dual_ of `unknown`. `never` is useful in many scenarios, and one such use case is when type refinements proves it impossible: `never` is also said to be the _bottom_ type, meaning there doesn't exist a value that inhabits the type `never`. In fact, it is the _dual_ of `unknown`. `never` is useful in many scenarios, and one such use case is when type refinements proves it impossible:
@ -111,7 +111,7 @@ if typeof(x) == "number" and typeof(x) == "string" then
end end
``` ```
## `any` type ### `any` type
`any` is just like `unknown`, except that it allows itself to be used as an arbitrary type without further checks or annotations. Essentially, it's an opt-out from the type system entirely. `any` is just like `unknown`, except that it allows itself to be used as an arbitrary type without further checks or annotations. Essentially, it's an opt-out from the type system entirely.