On Wednesday, 8 August 2012 at 19:27:54 UTC, Walter Bright wrote:
The idea is to have hash act like a component - not with special added code the user has to write.
Sorry, but I think this is a meaningless statement without specifying what kind of interface the component should adhere to. In my opinion, the proposed std.hash design would be a perfectly valid interface for »accumulate stuff and at some point get a result«-type components.
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.
Hash functions are _not_ analogous to reduce(), because the operation performed by reduce() is stateless, whereas hash functions generally have some internal state.
»Continuing« a reduce() operation by repeatedly calling it with the last partial result as the starting value is only possible because there is no additional state to carry over. To make this work with hashes, you'd have to return something encapsulating the internal state from your hash function. But then, you again need to obtain the actual result from that return value from that result somehow, which defeats the original intent of making it work like reduce – and incidentally is what finish() does.
David
