string 在 Go 中将自定义类型转换为字符串
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Converting a custom type to string in Go
提问by DaveUK
In this bizarre example, someone has created a new type which is really just a string:
在这个奇怪的例子中，有人创建了一个新类型，它实际上只是一个字符串：
type CustomType string
const (
Foobar CustomType = "somestring"
)
func SomeFunction() string {
return Foobar
}
However, this code fails to compile:
但是，此代码无法编译：
cannot use Foobar (type CustomType) as type string in return argument
不能使用 Foobar（类型 CustomType）作为返回参数中的类型字符串
How would you fix SomeFunction so that it is able to return the string value of Foobar ("somestring") ?
您将如何修复 SomeFunction 以便它能够返回 Foobar ("somestring") 的字符串值？
回答by Cerise Limón
回答by Ravi
Better to define a Stringfunction for the Customtype- it can make your life easier over time - you have better control over things as and if the structure evolves. If you really need SomeFunctionthen let it return Foobar.String()
更好地定义一个String函数Customtype- 随着时间的推移，它可以让你的生活更轻松 - 当结构发生变化时，你可以更好地控制事物。如果你真的需要，SomeFunction那就让它回来Foobar.String()
package main
import (
"fmt"
)
type CustomType string
const (
Foobar CustomType = "somestring"
)
func main() {
fmt.Println("Hello, playground", Foobar)
fmt.Printf("%s", Foobar)
fmt.Println("\n\n")
fmt.Println(SomeFunction())
}
func (c CustomType) String() string {
fmt.Println("Executing String() for CustomType!")
return string(c)
}
func SomeFunction() string {
return Foobar.String()
}
回答by Ashish Tiwari
回答by Krishnadas PC
For every type T, there is a corresponding conversion operation T(x) that converts the value x to type T. A conversion from one type to another is allowed if both have the same underlying type, or if both are unnamed pointer types that point to variables of the same underlying type; these conversions change the type but not the representation of the value. If x is assignable to T, a conversion is permitted but is usually redundant. - Taken from The Go Programming Language - by Alan A. A. Donovan
对于每个类型 T，都有一个相应的转换操作 T(x) 将值 x 转换为类型 T。如果两者具有相同的基础类型，或者如果两者都是指向的未命名指针类型，则允许从一种类型转换为另一种类型到相同基础类型的变量；这些转换改变了类型而不是值的表示。如果 x 可分配给 T，则允许进行转换，但通常是多余的。- 摘自Go 编程语言 - 作者：Alan AA Donovan
As per your example here are some of the different examples which will return the value.
根据您的示例，这里是一些将返回值的不同示例。
package main
import "fmt"
type CustomType string
const (
Foobar CustomType = "somestring"
)
func SomeFunction() CustomType {
return Foobar
}
func SomeOtherFunction() string {
return string(Foobar)
}
func SomeOtherFunction2() CustomType {
return CustomType("somestring") // Here value is a static string.
}
func main() {
fmt.Println(SomeFunction())
fmt.Println(SomeOtherFunction())
fmt.Println(SomeOtherFunction2())
}
It will output:
它会输出：
somestring
somestring
somestring
