Bug #19530
closed
`Array#sum` and `Enumerable#sum` sometimes show different behaviours
Description
Hi everyone. 👋🏻
We recently discovered that Array#sum and Enumerable#sum will output different results in some edge cases.
Here's the smallest script I managed to write to reproduce the issue:
class Money
def initialize(amount)
@amount = amount.to_f
end
def +(other)
self.class.new(@amount + other.to_f)
end
def to_f
@amount
end
end
p [7.0].each.sum(Money.new(0)) #=> #<Money:0x00000001005b35f0 @amount=7.0>
p [7.0] .sum(Money.new(0)) #=> 7.0 💥
I understand that it is expected that #sum may not honor custom definitions of the #+ method (particularly when the summed values are Float).
However, I would like to bring your attention to the fact that, in the example above, calling #sum on an Array of Float values and calling #sum on an Enumerable that yields the same Float values will return results of different types.
I've reproduced the same behaviour with multiple versions of Ruby going from 2.6.5 to 3.2.1.
Ideally, I would expect [7.0].sum(Money.new(0)) to return a Money object identical to the one returned by [7.0].each.sum(Money.new(0)).
I think it would make sense if at least they returned an identical value (even if it is a Float).
Addendum: I forgot to mention this extract of the Array#sum documentation:
When no block is given, returns the object equivalent to:
sum = init array.each {|element| sum += element } sum
With the example above, it would indeed return a Money object.
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