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Object#hash
VALUE
rb_obj_hash(VALUE obj)
{
long hnum = any_hash(obj, objid_hash);
return ST2FIX(hnum);
}
Returns the integer hash value for self; has the property that if foo.eql?(bar) then foo.hash == bar.hash.
Class Hash uses both hash and eql? to determine whether two objects used as hash keys are to be treated as the same key. A hash value that exceeds the capacity of an Integer is truncated before being used.
Many core classes override method Object#hash; other core classes (e.g., Integer) calculate the hash internally, and do not call the hash method when used as a hash key.
When implementing hash for a user-defined class, best practice is to use Array#hash with the class name and the values that are important in the instance; this takes advantage of that method’s logic for safely and efficiently generating a hash value:
def hash [self.class, a, b, c].hash end
The hash value may differ among invocations or implementations of Ruby. If you need stable hash-like identifiers across Ruby invocations and implementations, use a custom method to generate them.