问题描述
我正在学习Rails，并遵循此线程.我被to_proc方法困住了.我仅将符号视为字符串的替代方法(它们类似于字符串，但在内存方面更便宜).如果我还有其他缺少的符号，请告诉我.请以简单的方式说明to_proc的含义及其用途.
I am learning rails and following this thread. I am stuck with the to_proc method. I consider symbols only as alternatives to strings (they are like strings but cheaper in terms of memory). If there is anything else I am missing for symbols, then please tell me. Please explain in simple way what to_proc means and what it is used for.
推荐答案
某些方法占用了一个块，并且这种模式经常出现在一个块上:
Some methods take a block, and this pattern frequently appears for a block:
{|x| x.foo}
，人们希望以更简洁的方式写出来.为此，将符号，方法Symbol#to_proc，隐式类强制转换和&运算符组合使用.如果在参数位置中将&放在Proc实例的前面，则它将被解释为一个块.如果将Proc实例以外的其他内容与&组合，则隐式类强制转换将尝试使用在该对象上定义的to_proc方法(如果有)将其转换为Proc实例.在Symbol实例的情况下，to_proc以这种方式工作:
and people would like to write that in a more concise way. In order to do that, a symbol, the method Symbol#to_proc, implicit class casting, and & operator are used in combination. If you put & in front of a Proc instance in the argument position, that will be interpreted as a block. If you combine something other than a Proc instance with &, then implicit class casting will try to convert that to a Proc instance using to_proc method defined on that object if there is any. In case of a Symbol instance, to_proc works in this way:
:foo.to_proc # => ->x{x.foo}
例如，假设您这样编写:
For example, suppose you write like this:
bar(&:foo)
&运算符与不是Proc实例的:foo结合使用，因此隐式类强制将Symbol#to_proc应用于它，从而得到->x{x.foo}. &现在适用于此，并解释为一个块，给出:
The & operator is combined with :foo, which is not a Proc instance, so implicit class cast applies Symbol#to_proc to it, which gives ->x{x.foo}. The & now applies to this and is interpreted as a block, which gives:
bar{|x| x.foo}
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