This method is only available on newer versions.
The first available version (v2_6_3) is shown here.
size()
public
Returns the total size of the
enumerator chain calculated by summing up the size of each enumerable in the chain. If
any of the enumerables reports its size as nil or Float::INFINITY, that
value is returned as the total size.
static VALUE
enum_chain_size(VALUE obj)
{
return enum_chain_total_size(enum_chain_ptr(obj)->enums);
}