Actually, the default is overflow I now realize. But there is also automatic promotion, so: 0 + typemax(UInt8)+ typemax(UInt8) 510 While adding UInt8

Actually, the default is overflow I now realize. But there is also automatic promotion, so: 0 + typemax(UInt8)+ typemax(UInt8) 510 While adding UInt8 first, then an implicit Int64 causes overflow: typemax(UInt8)+ typemax(UInt8) 254 (ie: 255 overflows to 254 - or is promoted and sums to 510) See: https://docs.julialang.org/en/v1/manual/integers-and-floating-point-numbers/ https://docs.julialang.org/en/v1/manual/integers-and-floatin... Try: https://julialang.org/learning/tryjulia/ https://julialang.org/learning/tryjulia/