将 nil 强制转换为数字
这里发生了什么？
irb(main):001:0> a= nil
=> nil
irb(main):002:0> b = nil
=> nil
irb(main):003:0> a
=> nil
irb(main):004:0> a+b
NoMethodError: undefined method `+' for nil:NilClass
from (irb):4
from :0
irb(main):005:0> if a.nil? or b.nil?; a,b=0;end;
irb(main):006:0* c = a+b
TypeError: nil can't be coerced into Fixnum
from (irb):6:in `+'
from (irb):6
from :0
irb(main):007:0>
如何通过将 nil 转换为数字来安全地执行算术？
What is happening here??
irb(main):001:0> a= nil
=> nil
irb(main):002:0> b = nil
=> nil
irb(main):003:0> a
=> nil
irb(main):004:0> a+b
NoMethodError: undefined method `+' for nil:NilClass
from (irb):4
from :0
irb(main):005:0> if a.nil? or b.nil?; a,b=0;end;
irb(main):006:0* c = a+b
TypeError: nil can't be coerced into Fixnum
from (irb):6:in `+'
from (irb):6
from :0
irb(main):007:0>
How can you safely perform arithmetic by transforming nil to an number?
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根据为什么是 nil 而不是数字，您可以决定将 nil 视为 0 对您有好处；在这种情况下，你可以这样做：
当然，只有当你知道为什么你有一个 nil 而不是一个数字时，这才有意义......
Depending on why there's a nil instead of a number, you could decide that it's good for you to consider nil as 0; in that case, you can do something like:
This, of course, only makes sense if you know why you have a nil instead of a number...
为什么要添加
nil？它被专门设计为表示缺少值的东西（注意：nil不是0）。如果您真正想要做的是将两个值设置为
0（如果其中一个值当前nil），那么您真正想要的是：上面代码中的错误是
a,b=0部分，它仅将a的值设置为0- 它设置了b到nil因为左侧正在寻找两个值，而右侧只提供了一个（因此其他值被假定为nil）。Why would you want to add
nil? It's specifically designed to be something that represents the lack of a value (note:nilis NOT0).If what you're actually wanting to do is set both values to
0if either is currentlynil, then what you actually want is this:Your mistake in the code above was the
a,b=0portion, which only sets the value ofato0- it setsbtonilbecause the left hand side is looking for two values, and only one is provided on the right (so the others are assumed to benil).您的并行分配 (
a, b = 0) 会产生a=0和b=nil，即分配0code> 到a和nil到b，因为右侧只有一个值。你想要的是：
如果a.nil？或b.nil？； a = b = 0;结尾
c = a + b
显然，代码仍然有问题，因为当
a或b为零。Your parallel assignment (
a, b = 0) results ina=0andb=nil, i.e. it assigns0toaandniltob, because there is only one value on the right hand side.What you want is:
if a.nil? or b.nil?; a = b = 0; end
c = a + b
Obviously the code is still broken, since you overwrite any non-nil values of
aandbwith 0 whenaorbis nil.