RFC: 'noinfer' Type Operator

[hardlyardi]

Rendered

[deviaze]

We def need this functionality in the new solver, but I think I'd prefer it being a @noinfer attribute instead of an annotation that looks like a type function.

For example (using ariel's example from discord):

local function greedy_insert<V>(tbl: { V }, value: @noinfer V)
  -- ...
end
local a: "a"
local b: "b"
local some_table = { a, b }
local c: "c"
greedy_insert(some_table, c) -- TypeError: Type '"c"' could not be converted into '"a" | "b"'

[daimond113]

I think using generic constraints once they are implemented instead of adding a separate feature for this will be better. For example, a simple setter function in TypeScript looks like this:

function set<const S, V extends S>(source: S, value: V)

This leverages generic constraints to emulate greediness without requiring a separate feature.