[英]Ruby: Difference between passing `&proc` and `proc` to a method
I have a bit of code modified slightly from a question on codeacademy. 我对codeacademy的问题做了一些修改。 The code is :
代码是:
def print_list(array, first = 1)
counter = first
array.each do |array|
puts "#{yield counter} #{array}"
counter = counter.next
end
end
proc = Proc.new do |n|
"[#{100*n}]:"
end
print_list ["alpha", "beta", "gamma"], 5, &proc
If I remove the & from the last line Ruby throws me an argument error. 如果我从最后一行删除&,Ruby会抛出参数错误。 What is the purpose of the & here?
&这里的目的是什么?
If you remove the &
, then print_list
treats proc
as a third argument to itself, instead of a block. 如果删除
&
,则print_list
将proc
视为自身的第三个参数,而不是块。 The &
symbol transforms the Proc
object into a block, which is called inside print_list
by the yield
keyword. 的
&
符号变换Proc
对象成块,其被称为内部print_list
由yield
关键字。
More succinctly, proc
is just an argument, &proc
is a reference to the block passed to the method. 更简洁地说,
proc
只是一个参数, &proc
是对传递给该方法的块的引用。
You might find this article useful to understand the differences between proc and blocks 您可能会发现本文对理解proc和块之间的区别很有帮助
The & indicates that the proc should be passed as a block. &表示proc应该作为一个块传递。
Without it, the "proc" will just be another (third) parameter so you'll get the argument error (3 for 2) 没有它,“ proc”将只是另一个(第三个)参数,因此您将得到参数错误(3个代表2)
It's possible to pass it without the & and use it in your print_list method directly as a proc... but first can't be optional then. 可以在不带&的情况下传递它,并直接将它作为proc在您的print_list方法中使用...但是首先不能是可选的。 You'll need to pass first or at the very least nil.
您需要先通过,或者至少要通过。
def print_list(array, first, proc)
counter = first || 1
array.each do |array|
puts "#{proc.call counter} #{array}"
counter = counter.next
end
end
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