UInt64

UInt64 stores values from 0 through 18_446_744_073_709_551_615.

local sequence: UInt64 = 4_000_000_000
local next = sequence + 1
print(`sequence={next}`)

No signed integer type contains the entire UInt64 range. Int64(sequence) therefore performs a checked conversion and may trap. Float64(sequence) is always representable as a finite float but may round because Float64 cannot represent every 64-bit integer exactly.