Issue #12902 has been updated by Jeremy Daer.


If we treated the first argument to `#sum` as the additive identity instead of "initial element," then it'd be very clear what to expect:

When there are no elements in the Enumerable, return the identity.

That works nicely for summing non-numeric/string/etc objects:

~~~ ruby
payments.none? # => true
payments.sum(Payment.new(0)) # => Payment.new(0)
~~~

Plus, it's backward compatible, doesn't break existing behavior.

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Feature #12902: How about Enumerable#sum uses initial value rather than 0 as default?
https://bugs.ruby-lang.org/issues/12902#change-61449

* Author: Aaron Lasseigne
* Status: Feedback
* Priority: Normal
* Assignee: 
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In https://bugs.ruby-lang.org/issues/12217#note-3, Akira Tanaka, mentions that the default argument to sum is 0. This creates problems with non-numeric summations (e.g. strings). This would make the method more flexible. It also makes it behave more like `reduce`. I think using the initial value in the enumerable is less surprising than using 0.



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