# `debug.id`

## Summary

Add `debug.id` which accepts a value and always returns the identifier unique to that value.

## Motivation

When debugging, it is often useful to compare identity. Usually `print` will print the memory address of the table or userdata, but when `__tostring` is overriden, the address becomes unobtainable.

`rawequal` can compare equality between two arguments, but is not suitable for a human comparing output between two `print` calls or between keys or values in a table.

## Design

`debug.id(value: any)` always returns the identifier unique to that value, and is not possible to override.

While tables and userdata have individualized metatables, also allowing functions and threads to be passed to `debug.id` would let their type-level `__tostring` be redefined. Strings are useful to accept because of long, similar strings.

## Drawbacks

None known.

## Alternatives

Lua has `string.format("%p", {})`, but this is an invalid format option in Luau and less obvious.

If not implemented, it remains annoying to compare identity when dealing with tables or userdata that override `__tostring`.