将 Ruby 符号理解为方法调用 [英] Understanding Ruby symbol as method call

问题描述

class A
   def test
       "Test from instance"
   end
   class << self
       def test
           "Test from class"
       end
    end
end

p A.send(:test)    # "Test from class"
p A.new.method(:test).call  # "Test from instance"

此处符号按预期工作，但此处:

Here symbol works as expected, but here:

s="test"
s1=:s
p s1   # :s

为什么 :s 打印在这里??我不明白这背后的原因.谁能帮我解释一下?

why :s is printed here?? I dont understand the reason behind it. Can anyone please explain for me ?

推荐答案

符号是一种轻量级的字符串(尽管它们不是字符串).send() 和 method() 方法可以接受字符串或符号；一个在内部工作中转换为另一个(不确定是哪个)，然后 ruby​​ 执行具有匹配名称的方法.因此 A.send(:text) 等价于 A.text().如果您有一个名为 methodName = :text 的变量，您可以执行 A.send(methodName) 而不是 A.methodName().

Symbols are sort of lightweight strings (though they are not strings). The send() and method() methods can take strings or symbols; one is converted to the other in the inner workings (not sure which) and then ruby executes the method with the matching name. Hence A.send(:text) is equivalent to A.text(). If you had a variable named methodName = :text, you could do A.send(methodName) but not A.methodName().

符号不是变量，因此您不能为符号赋值.在您的示例中，符号 :s 与变量 s 无关(尽管它们具有相同的名称"，但在其前面加上冒号使其成为符号而不是变量).您正在为变量 s 分配一个字符串值，但告诉它打印符号 :s，它确实这样做了.

Symbols are not variables, so you can't assign a value to a symbol. In your example, the symbol :s is unrelated to the variable s (despite the fact that they have the same "name", preceding it with a colon makes it a symbol instead of a variable). You're assigning a string value to the variable s but telling it to print the symbol :s, which it does.

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