The review of std.hash package

[Johannes Pfau]

Am Wed, 08 Aug 2012 12:27:39 -0700
schrieb Walter Bright <newshound2 at digitalmars.com>:

> On 8/8/2012 12:08 PM, Johannes Pfau wrote:
> > No where's the difference, except that for hashes the context
> > ('hash') has to be setup and finished manually?
> 
> 
> The idea is to have hash act like a component - not with special
> added code the user has to write.
Please explain that. Nobody's going to simply replace a call to reduce
with a call to a fictional 'hashReduce'. Why is it so important that
reduce + hash API's match 100% even if the API doesn't fit hashes?

> 
> In this case, it needs to work like a reduce algorithm, because it is
> a reduce algorithm. Need to find a way to make this work.
> 

We could do some ugly, performance killing hacks to make it possible,
but I just don't see why this is necessary.

----
struct InterHash
{
    MD5 ctx;
    ubyte[16] finished;
    alias finished this;
}

InterHash hashReduce(Range)(Range data)
{
    InterHash hash;
    hash.ctx.start();
    return hashReduce(hash, data);
}

InterHash hashReduce(Range)(InterHash hash, Range data)
{
    copy(data, hash);
    auto ctxCopy = hash.ctx;
    hash.finished = ctxCopy.finish();
    return hash;
}

auto a = hashReduce([1,2,3]);
auto b = hashReduce(a, [3,4]);
----

However, a and b are still not really valid hash values. I just don't
see why we should force an interface onto hashes which just doesn't fit.