Deprecate hashvalue vtable

[dukeleto]

The hashvalue VTABLE is unused in Parrot core and has no tests, until I added some in the t/src/extend_vtable.t file as part of my TPF grant to improve the docs/tests of our embed/extend system.

It has been added to api.yaml and will be eligible for removal in 3.6.

[bacek]

Hello.

-1 from. I'm pretty sure it's used. I've implemented it to support PMC keys in Hashes. Currently it's defained only in Default PMC as fallback, but any HLLs can provide own hashing functions.

-- Bacek

[luben]

VTABLE_hashvalue it is used in the hash-tables. When using PMC keys we get PMC's hashvalue. Every PMC could override the default implementation in order to provide faster or more appropriate hashing.

In short run, removing hashvalue vtable will give us more speed (because of less indirection) but also less flexibility. In long run, it will stop some optimizations - every PMC knows what represents best its identity and how most efficiently to calculate a hashvalues if itself.

[nwellnhof]

This VTABLE function is absolutely crucial. How are PMCs supposed to define their own hashvalue implementations without it?

[dukeleto]

If it is crucial, shouldn't we have a test for it? Am I missing something, or is this not tested?

[bacek]

Hello.

t/pm/hash.t, pmc_keys sub. Not comprehensive though.

-- Bacek.

[bacek]

Hello.

It's comprehensive now :)

-- Bacek