User-Defined Type Functions

[toxamin]

What lua version(s) is this feature from?

Luau

What feature are you requesting?

Luau has user-defined type functions.

type function rawget(tbl, key)
    if not tbl:is("table") then
        error("first parameter must be a table type!")
    end

    for k, v in tbl:properties() do
        if k == key then
            if v.read ~= v.write then
                error("mismatched read/write types found for the property")
            end

            return v.read
        end
    end

    error("key not found!")
end

type Person = {
    name: string,
    age: number
}

type ty = rawget<Person, "name"> -- resolves to `ty` defined as `string`

Can you go in further detail of what this feature is about?

No response

Please ensure you have done the following actions:

• I have checked that there are no similar requests already open.
• I have confirmed that this has not been implemented on the latest nightly version.
• I have confirmed that this is a custom syntax that requires modifications to be supported.
• I acknowledge my issue will be closed if any step has been skipped.