Re: [boost] [hash2][review] Early review (due to holidays)

Claudio DeSouza wrote:

I tend to disagree. In my opinion even this:

hash.update( as_bytes( span{st} ) );

Is better than this:

hash.update( v.data(), v.size() );

Maybe. But the two cases with the current interface are consistent - you do the same thing for both vector and string - and the two cases with the "normal" span aren't. I would prefer a span-style interface where the two cases look the same, like this hash.update( v ); hash.update( st ); There'd be no questions here as to whether this is a usability gain compared to the current interface. (Ideally, in a hypothetical stdlib, .data would return a span and the above would be hash.update( v.data() ); hash.update( st.data() ); to make it explicit that we're dropping to a lower level interface, but one can't have everything.)

Something like as_byte_span is just an extra nicety, but I think it is easy to underestimate how you can avoid mistakes with the first example as opposed to the second.

On Wed, Dec 4, 2024 at 2:38 PM Peter Dimov via Boost wrote:

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Claudio DeSouza wrote:

...

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So I switched `update` back to void const*. The "type safety" gains aren't worth the substantial decrease in usability.

In my experience, the usability/readability gains are on the side of using span. This may involve providing extensions, but at the end of the day you get more C++-friendly constructs.

Well... no, they aren't.

Suppose you have the data in `std::vector<unsigned char> v`. With the current `update` that's

hash.update( v.data(), v.size() );

And if you have the data in `std::string st`, that's

hash.update( st.data(), st.size() );

Now suppose `update` takes `span<unsigned char const>`. For `v`, this is

hash.update( v );

which is nice; but for `st`, that would be (assuming C++17)

hash.update( as_bytes( span{st} ) );

which is not so nice.

In Chromium you have as_byte_span, which does as_bytes(span(x)), so it'd be better.

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