how do i check if a variable is undefined/null?

[odd wharf]

1. cant check for undefined 2. compare against null if the value is an optional (?T)

if you just have T, you cant (what would a null T thats not an optional mean?)

what is uninit data?

[timid cosmos]

yes, it's poison, you must initilaise it before use.

undefined is for cases where you have external knowledge of whether some variable is initialised, null is for the cases where you don't

in the case of an fresh allocation, you know the data there is uninitialised and so it's filled with undefined