英文:
How to print an object
问题
如何在引用对象时更改puts打印的内容？
考虑以下代码：
class MyClass
attr_accessor :var
def initialize(var)
@var = var
end
# ...
end
obj = MyClass.new("content")
puts obj # 打印 #<MyClass:0x0000011fce07b4a0>，但我希望它打印 "content"
英文:
How do you change what is printed with puts when an object is referenced?
Consiser the following code:
class MyClass
attr_accessor :var
def initialize(var)
@var = var
end
# ...
end
obj = MyClass.new("content")
puts obj # Prints #<MyClass:0x0000011fce07b4a0> but I want it to print "content"
I imagine that there is an operator that you can overload (or something similar), but I don't know what it's called so I have no clue what to search for to find the answer.
答案1
得分: 1
class MyClass
attr_accessor :var
def initialize(var)
@var = var
end
def to_s
@var
end
end
obj = MyClass.new("content")
puts obj # 打印 "content"
英文:
class MyClass
attr_accessor :var
def initialize(var)
@var = var
end
def to_s
@var
end
end
obj = MyClass.new("content")
puts obj # Prints "content"
答案2
得分: 1
摘自puts文档：
puts(*objects)→nil将给定的对象写入流中，该流必须处于可写状态；返回
nil。对于不以换行序列结尾的每个对象，在其后写入一个换行符。[...]对每个对象的处理：
- 字符串：写入字符串。
- 既不是字符串也不是数组：写入
object.to_s。- 数组：写入数组的每个元素；数组可以嵌套。
这意味着：您传递给puts的对象不是字符串，因此，在将字符串输出到IO之前，Ruby会调用该对象的to_s方法。因为您的对象没有实现to_s方法，所以将使用从Object#to_s继承的默认实现。
要返回自定义输出，只需像这样添加自己的to_s方法到您的类中：
class MyClass
attr_accessor :var
def initialize(var)
@var = var
end
def to_s
var
end
end
英文:
Quote from the documentation of puts:
> puts(*objects) → nil
>
> Writes the given objects to the stream, which must be open for writing; returns nil. Writes a newline after each that does not already end with a newline sequence. [...]
>
> Treatment for each object:
>
> - String: writes the string.
> - Neither string nor array: writes object.to_s.
> - Array: writes each element of the array; arrays may be nested.
That means: The object you pass to puts is not a string, therefore, Ruby will call to_s on that object before outputting the string to IO. Because your object has no to_s method implemented, the default implementation from Object#to_s.
To return a customize output, just add your own to_s method to your class like this:
class MyClass
attr_accessor :var
def initialize(var)
@var = var
end
def to_s
var
end
end
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