struct String()实现导致Sprintf"+"堆栈溢出.旗帜 [英] struct String() implemention causes stack overflow with Sprintf "+" flag

问题描述

Golang新手问题:为什么我不能不在String()实现方法中为结构体使用％+ v" 标志?

Golang noob question: Why can I not use the "%+v" flag for a struct in the String() implementation method?

我有一个要在其中实现 String()方法以进行漂亮打印的结构.我喜欢在此处给出的答案，但是我不喜欢键入，因此我尝试对其进行修改以返回字符串对结构使用％+ v" 格式标志.来自 fmt 文档:

I have a struct where I want to implement a String() method for pretty print. I like the answer given here, but I don't like to type, so I'm trying to modify it to return a string using the "%+v" format flag for structs. from the fmt doc:

％v在打印结构时使用默认格式的值，加号(％+ v)添加字段名称

%v the value in a default format when printing structs, the plus flag (%+v) adds field names

如果我简单地使用 fmt.Printf(％+ v"，color)调用它，那么效果很好，但是如果我尝试将 + 标志放在 String()实现，我发生了堆栈溢出(我第一次有机会在stackoverflow.com上问堆栈溢出"问题；))

This works fine if I simply call it with fmt.Printf("%+v", color), but if I try to put the + flag in the String() implementation, I get a stack overflow (my first chance to ask a "stack overflow" question on stackoverflow.com ;) )

我确定我在这里不理解指针引用，否则会有一些递归.我怀疑这个菜鸟发现了我的第一个Golang错误，所以有人可以解释一下吗?

I'm sure I'm not understanding a pointer reference here, or there is some recursion. I doubt this noob found my first Golang bug, so can someone please explain?

在此处查看围棋演示 https://play.golang.org/p/13_qI8Iwwa

推荐答案

请参见打包fmt文档:

除了使用动词％T 和％p 进行打印时，特殊格式注意事项适用于实现某些接口的操作数.按申请顺序:

Except when printed using the verbs %T and %p, special formatting considerations apply for operands that implement certain interfaces. In order of application:

1. 如果操作数实现方法 String()string ，则将调用该方法将对象转换为字符串，然后将其转换为字符串根据动词的要求进行格式设置(如果有的话).

1. If an operand implements method String() string, that method will be invoked to convert the object to a string, which will then be formatted as required by the verb (if any).

在诸如此类的情况下避免递归

type X string 
func (x X) String() string { return Sprintf("<%s>", x) }

在重复发生之前转换值:

convert the value before recurring:

func (x X) String() string { return Sprintf("<%s>", string(x)) }

无限递归也可以由自引用数据触发结构，例如包含自身作为元素的切片该类型具有String方法.但是，这种病理很少见，并且该包装无法防止它们受到侵害.

Infinite recursion can also be triggered by self-referential data structures, such as a slice that contains itself as an element, if that type has a String method. Such pathologies are rare, however, and the package does not protect against them.

---

内部:

func (c Color) String() string {
    // THIS CAUSES STACK OVERFLOW
    return fmt.Sprint(c)
}

致电

fmt.Sprint(c)

再次递归调用 func(c Color)String()字符串的

或 fmt.Println(c)会导致溢出:请在

or fmt.Println(c) which calls func (c Color) String() string again recursively causes overflow: try it on The Go Playground

这也可以正常工作: https://play.golang.org/p/NYLtrxUeiA

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