Re: [boost] [move] [range] move algorithm (was: interest: the pass-by-value...)

On 02/18/2014 10:30 AM, Neil Groves wrote:

On Tue, Feb 18, 2014 at 5:32 PM, Eric Niebler wrote:

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On 02/18/2014 09:16 AM, Adam Wulkiewicz wrote:

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Hi Eric,

Eric Niebler wrote:

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On 02/15/2014 02:17 PM, Adam Wulkiewicz wrote:

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There is already boost::move_iterator in Boost.Move Please make sure that move iterators and ranges are Input and not anything else, regardless of what the standard says. The standard is dangerously wrong in this regard.

Thanks for the advice. It's because the user might by mistake go through some elements more than once which would result in some number of moves from the same element or do you have something more surprising in mind?

That's it precisely. And using move iterators in standard algorithms that assume anything other than Input is pretty much guaranteed to make you very unhappy.

I agree that many scenarios would end in much unhappiness! I disagree that unhappiness is pretty much guaranteed. I believe there are valid scenarios that would be broken by increasing the requirements to demand single-pass traversal. The most common case that I think would be broken in my own code is where I am using a random-access iterator to stride.

Why in the world does a stride iterator need to be random-access? Here is a strided range adaptor that works with input iterators: https://github.com/ericniebler/range-v3/blob/master/include/range/v3/view/st... It's not even hard. Eric