Question

def accum(start, items) 
    result, items = start, items.dup
    yield(result, items.pop) until items.empty?
    result
end

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
puts accum(0, numbers) { |a, b| a + b }
puts accum(1, numbers) { |a, b| a * b }

# 0
# 1

在Ruby版本中：
2.1.5p273（2014-11-13修订版48405）[x64-mingw32]
1.9.3p194（2012-04-20）[i386-mingw32]

输出

#0
#1

我希望数组中的所有数字能够求和并加倍实际乘法和求和没有发生的原因是什么。

Answer 1

您永远不会使用来自yield的块的返回值。它应该是这样的：

result = yield(result, items.pop) until items.empty?

我必须注意到你正在重新发明轮子。您的累积函数已经在Ruby标准库中实现，称为reduce或inject（两种方式都有效）：

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
puts numbers.reduce {|a, b| a + b }
# But hey, we're just calling a single function with 2 args in that block
# Let's specify a symbol that corresponds to a function!
# Works pretty much the same way
puts numbers.reduce(:+)
# For multiplication too
puts numbers.reduce(:*)

Answer 2

将result设置为从yield获得的值：

def accum(start, items) 
    result, items = start, items.dup
    result = yield(result, items.pop) until items.empty?
    result
end

ruby中的累积函数不起作用

2 个答案: