在Ruby中创建一个需要额外参数的setter方法 [英] Creating a setter method that takes extra arguments in Ruby

问题描述

我正在尝试编写一种充当设置器的方法，该方法除了分配的值外还接受一些额外的参数.愚蠢的例子:

I'm trying to write a method that acts as a setter and takes some extra arguments besides the assigned value. Silly example:

class WordGenerator
  def []=(letter, position, allowed)
    puts "#{letter}#{allowed ? ' now' : ' no longer'} allowed at #{position}"
  end

  def allow=(letter, position, allowed)
    # ...
  end
end

将其写为索引器是可行的，我可以这样称呼它:

Writing it as an indexer works and I can call it like this:

gen = WordGenerator.new

gen['a', 1] = true
# or explicitly:
gen.[]=('a', 1, true)

但是当我尝试以下任何一种方法时，口译员都会抱怨:

But when I try any of the following, the interpreter complains:

gen.allow('a', 1) = false # syntax error
gen.allow=('a', 1, false) # syntax error

为什么不起作用，我错过了明显的地方吗?

Why won't this work, am I missing the obvious?

推荐答案

它不起作用，因为解析器不允许.在形式为identifier = expression，expression.identifier = expression(其中标识符为\w+)，expression[arguments] = expression和expression.[]= arguments的表达式中，以及作为字符串，符号或字符文字(?=)的一部分，均允许使用等号.就是这样.

It doesn't work because the parser doesn't allow it. An equals sign is allowed in expressions of the form identifier = expression, expression.identifier = expression (where identifier is \w+), expression[arguments] = expression and expression.[]= arguments and as part of a string or symbol or character literal (?=). That's it.

gen.send(:allow=, 'a', 1, false)可以工作，但是那时候您也可以给该方法指定一个不包含=的名称.

gen.send(:allow=, 'a', 1, false) would work, but at that point you could as well just give the method a name that doesn't include a =.

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