why the result of tuple to union using T[number] is disorder

[HomyeeKing]

version : ^4.0.3

you can find code here

or just look at this

type A = [1,2,3]
type B = A[number]

// expect ^= type B = 1 | 2 | 3
// output:  ^= type B = 3 |  1 | 2

I know it doesn't effect using, but I wonder the order mechanism

[ajafff]

Types in unions are (most of the time) ordered in the order they were encountered when checking your code. This order is not guaranteed (see #17944 and linked issues) and may change in every compiler version or by changing your code just a tiny bit.

In your example 3 is encountered first as the length of the tuple, then the numeric literals 1, 2 and 3 again.
If you change your code a bit, you get a different order:

type A = [0,1,2,3]
type B = A[number] // 0 | 1 | 2 | 3

[HomyeeKing]

@ajafff ok , thanks
I think it depend the algrithom behind the processor
we'd better give in to performance