From the documentation of rb_obj_hash:
> Certain core classes such as Integer use built-in hash calculations and
> do not call the #hash method when used as a hash key.
So if you override, say, Integer#hash it won't be used from rb_hash_aref
and similar. This avoids method lookups in many common cases.
This commit uses the same optimization in rb_hash, a method used
internally and in the C API to get the hash value of an object. Usually
this is used to build the hash of an object based on its elements.
Previously it would always do a method lookup for 'hash'.
This is primarily intended to speed up hashing of Arrays and Hashes,
which call rb_hash for each element.
compare-ruby: ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-linux]
built-ruby: ruby 3.1.0dev (2021-09-29T02:13:24Z fast_hash d670bf88b2) [x86_64-linux]
# Iteration per second (i/s)
| |compare-ruby|built-ruby|
|:----------------|-----------:|---------:|
|hash_aref_array | 1.008| 1.769|
| | -| 1.76x|
John Hawthorn