When one writes a module/package that implements a new type it is prudent
to provide a type-specific value hashing function. This is particularly
important for immutable types where hash codes and isequal are more tightly
coupled than they are with mutable types.
memhash_seed is a module/package specific constant that serves as the seed
value for hashing values of the new type.
Here is an example, my type-specific hashing for values of type ArbFloat
(extended precision floating point types)
where 'memhash_seed' is called has_arbfloat_lo
# a type specific hash function helps the type to 'just work'
const hash_arbfloat_lo = (UInt === UInt64) ? 0x37e642589da3416a : 0x5d46a6b4
const hash_0_arbfloat_lo = hash(zero(UInt), hash_arbfloat_lo)
# two values of the same precision
# with identical midpoint significands and identical radus_exponentOf2s hash
equal
# they are the same value, one is less accurate yet centered about the other
hash{P}(z::ArbFloat{P}, h::UInt) =
hash(z.significand1$z.exponentOf2,
(h $ hash(z.significand2$(~reinterpret(UInt,P)), hash_arbfloat_lo)
$ hash_0_arbfloat_lo))
On Tuesday, August 9, 2016 at 11:49:24 AM UTC-4, Páll Haraldsson wrote:
>
>
> A.
>
> julia> @less Base.memhash_seed
> ERROR: ArgumentError: argument is not a generic function
> in methods at ./reflection.jl:140
>
> I know what this means, but it would be nice for it to look up the source,
> and when it's actually a function (sometimes, I'm not sure of the right
> parameters..). Is there a way for @less, @which @edit (I guess always same
> mechanisim) to work? Maybe already ion 0.5? Easy to add? I like reading the
> source code to learn, and not have to google or search github or ask here..
>
> [apropos got me nowhere.]
>
>
> B.
>
> Bonus point, I think I know what memhash[_seed] is.. but what is it.
>
>
> C.
>
> Trying to google it:
>
> https://searchcode.com/codesearch/view/84537847/
>
> Language Lisp
> [Clearly Julia source code, elsewhere I've seen Python autodetected..]
>
> --
> Palli.
>
>
