如何确定`value.FieldByName(name)`是否找到了字段?

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英文:

How to figure out if `value.FieldByName(name)` finds the field?

问题

我正在尝试弄清楚如何在下面的示例中停止程序的执行,当field未找到时。

如果FieldByName(key)返回一个零值,我该如何警告用户未找到该字段?

field := mutable.FieldByName(key)

// 在调用.Type()之前需要确定字段是否存在
if field.X == Y {
  log.Fatalf("无法在Config对象中找到[%s]字段", key)
}

switch field.Type().Name() {
}
英文:

I'm trying to figure out how to stop the execution of my program when the field is not found in the example below.

If FieldByName(key) returns a zero Value how can I warn the user that the field was not found?

field := mutable.FieldByName(key)

// need to figure out if the field exists before calling .Type() on it
if field.X == Y {
  log.Fatalf("Unable to find [%s] in Config object", key)
}

switch field.Type().Name() {
}

答案1

得分: 5

正如你已经提到的,reflect 包的**文档**中指出:

FieldByName 根据给定的字段名返回结构体字段。如果未找到字段,则返回零值 Value。

这与类型的零值不同。在**Value 的文档**中,我们可以读到:

零值 Value 表示没有值。它的 IsValid 方法返回 false,其 Kind 方法返回 Invalid,其 String 方法返回 "",而其他所有方法都会引发 panic。大多数函数和方法都不会返回无效值。如果有一个函数返回无效值,它的文档会明确说明条件。

因此,虽然 Len 解决方案可能有效,但更具描述性的测试方式是:

if !field.IsValid() {
  log.Fatalf("无法在 Config 对象中找到 [%s] 字段", key)
}
英文:

As you've already mentioned, the documentation for the reflect package states:

>FieldByName returns the struct field with the given name. It returns the zero Value if no field was found

This is not the same as a type's zero value. Under the documentation for Value, we can read:

>The zero Value represents no value. Its IsValid method returns false, its Kind method returns Invalid, its String method returns "<invalid Value>", and all other methods panic. Most functions and methods never return an invalid value. If one does, its documentation states the conditions explicitly.

So, while the Len solution might work, a more descriptive way to test it is:

if !field.IsValid() {
  log.Fatalf(&quot;Unable to find [%s] in Config object&quot;, key)
}

huangapple
  • 本文由 发表于 2014年8月8日 06:23:42
  • 转载请务必保留本文链接:https://go.coder-hub.com/25193256.html
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