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Type Hinting

Type-hinting looks like this:

local var: string = "hello world"

It works with functions too:

local function myfunc(a: string, b: string): number
    return tonumber(a) + tonumber(b)
end

print(myfunc(1, "1")) --> This will emit a warning for argument type mismatch.

There's no effect on performance. This is implemented entirely during the compilation phase.

What types can I use?​

  • string
  • number
    • int
    • float
  • boolean/bool
  • function
  • table
  • userdata
  • void (return type only)

Prefix a ? to indicate nil-able types, e.g. ?string indicates that it may be nil or a string.

You can also use | to delimit alternatives, e.g. string|int indicates that it may be a string or an int.

Putting all of this together, we could also have e.g. ?string|int to indicate that it may be nil, a string, or an int.

info

This is a WIP feature, and it's very difficult to implement in a one-pass compiler. Allow tolerance for missing coverage, and report any bugs.