问题

我有一个要用Sprintf创建的字符串：

message := fmt.Sprintf("Unit %s has a Level of %v, but is of Category %v",
	*entity.Name, *entity.LevelCode, *entity.CategoryCode)

在entity中，这些变量是可以为nil的：

• Name 是一个 *string 类型
• LevelCode 是一个 *LevelCode 类型
• CategoryCode 是一个 *CategoryCode 类型

但是如果它们有值，我想要的是这个值，而不是指针。
（例如：Unit ABC has a Level of nil, but is of Category AdministrativeUnit）

在任何语言中，我会这样写：

message := fmt.Sprintf("Unit %s has a Level of %v, but is of %v Category",
	entity.Name != nil ? *entity.Name : "nil", entity.LevelCode != nil ? *entity.LevelCode : "nil", entity.CategoryCode != nil ? *entity.CategoryCode : "nil")

但是 Go 不允许三元运算符。如果我不处理nil值，Sprintf会抛出异常。

那么，我必须这样开始吗？

if entity.Name == nil && entity.LevelCode != nil && entity.CategoryCode != nil) {
   message := "Unit nil has a Level of nil, but is of nil Category"
}
else {
   if entity.Name != nil && entity.LevelCode != nil && entity.CategoryCode != nil) {
     message := fmt.Sprintf("Unit %s has a Level of nil, but is of nil Category",
	entity.Name != nil ? *entity.Name : "nil")
   }
   else {
      ...

     // 对于9种可能的nil或非nil值的组合，以及9种sprintf格式，需要编写大量的代码。
   }
}

有没有更简洁的方式来以格式化的方式输出变量的内容？

<details>
<summary>英文:</summary>

I have this string to create with a `Sprintf` 

```go
message := fmt.Sprintf(&quot;Unit %s has a Level of %v, but is of Category %v&quot;,
	*entity.Name, *entity.LevelCode, *entity.CategoryCode)

In entity, the variables are pointers that can be nil:

• Name is a *string
• LevelCode has a *LevelCode type
• CategoryCode has a *CategoryCode type

but if they have a value, I want this value and not the pointers.
(i.e. Unit ABC has a Level of nil, but is of Category AdministrativeUnit)

in any language, I would have wrote:

message := fmt.Sprintf("Unit %s has a Level of %v, but is of %v Category",
	entity.Name != nil ? *entity.Name : "nil", entity.LevelCode != nil ? *entity.LevelCode : "nil", entity.CategoryCode != nil ? *entity.CategoryCode : "nil")

But Go doesn't allow ternary operator. And if I don't take care of nil values, Sprintf will throw an exception.

So, do I have to start that way?

if entity.Name == nil && entity.LevelCode != nil && entity.CategoryCode != nil) {
   message := "Unit nil has a Level of nil, but is of nil Category"
}
else {
   if entity.Name != nil && entity.LevelCode != nil && entity.CategoryCode != nil) {
     message := fmt.Sprintf("Unit %s has a Level of nil, but is of nil Category",
	entity.Name != nil ? *entity.Name : "nil")
   }
   else {
      ...

     for 9 combinations of values nil or not nil values, and 9 sprintf formats?
   }
}

What the shortest way to dump my variables content in a formatted line?


</details>


# 答案1
**得分**: -3

谢谢，有了你的帮助，我成功地构建了这个函数。

```go
// value函数用于处理可能为空的指针，并在它们不为空时返回它们的值。
func value[T any](v *T) string {
	if v != nil {
		return fmt.Sprintf("%v", *v)
	} else {
		return "nil"
	}
}

这样调用它：

message := fmt.Sprintf("Unit %s has a Level of %v, but is of %v Category",
    value(entity.Name), value(entity.LevelCode), value(entity.CategoryCode))

只用了一个Sprintf语句就完成了五个语句的工作... 但它能正常工作。

// value treat pointers that can be nil, and return their values if they aren't.
func value[T any](v *T) string {
	if (v != nil) {
		return fmt.Sprintf("%v", *v)
	} else {
		return "nil"
	}
}

message := fmt.Sprintf("Unit %s has a Level of %v, but is of %v Category",
    value(entity.Name), value(entity.LevelCode), value(entity.CategoryCode))