For me, what’s confusing about the up-promotion of arithmetic operations is that you wind up with type-changes that you might not expect:
function foo() a = 0x01 println(typeof(a)) b = 0x02 a = a + b println(typeof(a)) end foo() I still find the change in type of a to be unexpected. Obviously I can resolve this by doing things like, function foo() a = 0x01 println(typeof(a)) b = 0x02 a::Uint8 = a + b println(typeof(a)) end foo() but that leaves me with another source of confusion: when should I be asserting the type of a variable vs doing something like, function foo() a = 0x01 println(typeof(a)) b = 0x02 a = uint8(a + b) println(typeof(a)) end foo() — John On Mar 1, 2014, at 3:30 PM, Stefan Karpinski <ste...@karpinski.org> wrote: > There's been many discussions of this before. The basic premise is simple: > all integer arithmetic is done in your native word size. When you store that > result somewhere, it is converted to the storage type. Since you can do most > operations on Int64s and then convert to Int32 and get the exact same answer, > this works out fine. I have yet to hear a really convincing argument for why > we shouldn't just do everything in native int size. > > > On Sat, Mar 1, 2014 at 6:26 PM, Stefan Karpinski <ste...@karpinski.org> wrote: > On Fri, Feb 28, 2014 at 8:49 AM, andrew cooke <and...@acooke.org> wrote: > defining > Base.promote_rule(::Type{Int32}, ::Type{Int32}) = Int32 > doesn't help either, and i'm not sure why. > > Promotion only applies when the types don't already have the same type. When > you write int32(1) + int32(2) you call this method: > https://github.com/JuliaLang/julia/blob/master/base/int.jl#L16, which > explicitly converts the values to your native Int type and then does the work. >