The problem and a potential source of confusion is that the trait is named 'Zero' when a more proper name would be 'AdditiveIdentity'. There could be separate trait to indicate zero, but I don't know how much value such a trait would have. Here's the formal definition of additive identity from wikipedia:
Let N be a set which is closed under the operation of addition, denoted +. An additive identity for N is any element e such that for any element n in N, e + n = n = n + e Example: The formula is n + 0 = n = 0 + n. That's the reason it doesn't require the Mult trait. > On 09 Apr 2014, at 11:18, Rémi Fontan <remifon...@yahoo.fr> wrote: > > thanks for all your replies. I understand that zero has a specific meaning to > addition, and as well as multiplication, but for some reason does not require > the mul trait. > > implementing default sounds like a reasonable solution for my case. I > initially wanted to implement zero for my matrix4x4. I haven't implemented > add as I don't think I'm going to be adding matrix so I did not bother. > making default return [0...0] would work as well. > > cheers, > > Rémi > > > >> On Wed, Apr 9, 2014 at 5:20 AM, Kevin Ballard <ke...@sb.org> wrote: >>> On Apr 7, 2014, at 1:02 AM, Tommi Tissari <rusty.ga...@icloud.com> wrote: >>> >>>> On 07 Apr 2014, at 08:44, Nicholas Radford <nikradf...@googlemail.com> >>>> wrote: >>>> >>>> I think the original question was, why does the zero trait require the add >>>> trait. >>>> >>> If that was the original question, then my answer would be that >>> std::num::Zero requires the Add trait because of the way it is specified: >>> "Defines an additive identity element for Self". Then the question becomes: >>> "why is Zero specified like that?", and I would answer: because then you >>> can use it in generic algorithms which require their argument(s) to have an >>> additional identity. >> >> If you want a zero value for a type that doesn't support addition, >> std::default::Default may be a good choice to use. Semantically, that >> actually returns the "default value" for a type instead of the "zero value", >> but in a type without addition, how do you define "zero value"? >> >> -Kevin >> >> _______________________________________________ >> Rust-dev mailing list >> Rust-dev@mozilla.org >> https://mail.mozilla.org/listinfo/rust-dev > > > > -- > Rémi Fontan : remifon...@yahoo.fr > mobile: +64 21 855 351 > 93 Otaki Street, Miramar 6022 > Wellington, New Zealand
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