Lua any vs typescript any

[sloonz]

With typescript any, you can do anything with an any, and it will just happily return anything :

const x: any;
const y = x.foo; // Will work, y will have any type
const z = x.bar(1, "hello", y) // Will work too, z is still any

For dealing with untyped external stuff, I strongly prefer the typescript approach. I would like to achieve the same thing with teal ; here is what I came up with :

global type Any = record
	metamethod __index: function(Any, string): Any
	metamethod __call: function(...: any): Any...
end

Which kinda works :

local x: Any
x.foo.bar(1, "hello", x.t).spam.egg() -- tl check OK

Weirdly, this doesn't :

local x: Any
x:foo() -- invalid key 'foo' in record 'x' of type Any

Is this a bug or am I missing something ?

[lenscas]

teal's any is like unknown in TS.

I am personally not against having a TS like any kind of thing but it should be reserved for interfacing with lua and nowhere else. Even TS has been slowly replacing where any is used and replacing them with unknown

[sloonz]

but it should be reserved for interfacing with lua and nowhere else

Yeah, that’s my primary use-case. Writing (((ExternalTable as {string: any}).ExternalFunction) as function(...: any): any...) gets very tedious very fast.

[hishamhm]

The goal is to drive people to write .d.tl files with typed definitions for the Lua libraries they're interfacing with, rather than keeping considerable chunks of their code untyped. If you require("mylib") which is an untyped Lua library, you can keep that in Lua, but add to Teal's lookup path a file mylib.d.tl with only a record definition with the types of the public functions. Your code will still run using the Lua library, but the compiler will typecheck it using the definition file. The community maintains a collection of definition files for popular libraries at https://github.com/teal-language/teal-types.

Having said that, Teal does have a type like the one you expect: it's called unknown (yes, the names are flipped when compared to TypeScript...) but currently you can't declare it explicitly from Teal code.

However, if you run Teal in "lax mode", which is the default mode when typechecking files with the .lua extension (instead of .tl), then any variable that does not have a declared type will automatically be typed unknown, and no typechecks happen to them. The intention here was to allow users to take their .lua codebase and gradually add types until they're ready to switch to .tl.