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unless Enumerable.method_defined? :sum
module Enumerable
# Sums up elements of a collection by invoking their `+` method.
# Most useful for summing up numbers.
#
# @param initial [Object] an optional initial value.
# It defaults to 0 for an empty collection.
# @return The sum of the elements, or the initial value if there
# are no elements.
#
# @example
# [1, 2, 3].sum #=> 6
# [[1], [2], [3]].sum #=> [1, 2, 3]
# [].sum #=> 0
# ["a"].sum #=> "a"
# ["b", "c"].sum("a") #=> "abc"
def sum(initial = nil)
if initial
reduce(initial, &:+)
else
reduce(&:+) || 0
end
end
end
end
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