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Remove type refinements section

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We recently devoted significant effort to get this in a pretty good state where it works intuitively. As a result, this section is outdated. I'm deleting this because I think it's redundant to explain the same thing that intuition would also say.
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Alexander McCord 2021-09-23 12:09:43 -07:00 • committed by GitHub
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@ -317,42 +317,6 @@ local account: Account = Account.new("Alexander", 500)
--^^^^^^^ not ok, 'Account' does not exist --^^^^^^^ not ok, 'Account' does not exist
``` ```
## Type refinements
When we check the type of a value, what we're doing is we're refining the type, hence "type refinement." Currently, the support for this is somewhat basic.
Using `type` comparison:
```lua
local stringOrNumber: string | number = "foo"
if type(x) == "string" then
local onlyString: string = stringOrNumber -- ok
local onlyNumber: number = stringOrNumber -- not ok
end
local onlyString: string = stringOrNumber -- not ok
local onlyNumber: number = stringOrNumber -- not ok
```
Using truthy test:
```lua
local maybeString: string? = nil
if maybeString then
local onlyString: string = maybeString -- ok
end
```
And using `assert` will work with the above type guards:
```lua
local stringOrNumber: string | number = "foo"
assert(type(stringOrNumber) == "string")
local onlyString: string = stringOrNumber -- ok
local onlyNumber: number = stringOrNumber -- not ok
```
## Roblox types ## Roblox types
Roblox supports a rich set of classes and data types, [documented here](https://developer.roblox.com/en-us/api-reference). All of them are readily available for the type checker to use by their name (e.g. `Part` or `RaycastResult`). Roblox supports a rich set of classes and data types, [documented here](https://developer.roblox.com/en-us/api-reference). All of them are readily available for the type checker to use by their name (e.g. `Part` or `RaycastResult`).