| Re: [eigen] Signed or unsigned indexing |
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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] Signed or unsigned indexing
- From: Massimiliano Janes <max.jns@xxxxxxxxx>
- Date: Fri, 20 Jan 2017 17:53:55 +0100
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>
> On 20 Jan 2017, at 16:54, Francois Fayard <fayard@xxxxxxxxxxxxx> wrote:
>
> Let me give you my 2 cents on this signed/unsigned problem:
>
> - The core C++ language is using signed integers for indexing. If p is a pointer, p[k] is defined for k being a std::ptrdiff_t which is the Index type used by Eigen
> - The C++ standard library is using unsigned integers for indexing: std::size_t
actually, std random access iterators do accept signed indices as well. size_t indices are used at the container level only.
This actually makes sense to me, considering that interfaces should be minimal and that unsigneds has a simpler
set of invalid values when representing non negative quantities ( signeds need to specify the behaviour of
passing two bounds instead of one, this increases the complexity of documentation, pre/postcondition checks and tests ).
premising that I’m definitely in the signed party, I think most signed/size_t interoperability problems come from using
containers when iterators/ranges/views should be used; in my experience ( for what it’s worth :) ) if containers decays to views
ASAP most unsigned to signed indices conversions disappear, leaving just few controlled casts/checks where appropriate.