英文:
Golang insist that package-scoped function has a particular type
问题
如果我有一个类型别名FooType和一个函数Foo，有没有办法坚持Foo是FooType的实例。我想要一个明确的FooType，这样我就可以在类型切换中使用它。
如果可以的话，我不想使用var和函数字面量，因为这样当我尝试重新定义一个函数时就不会出错。
package main
import (
"fmt"
"reflect"
)
type FooType func(a int, b float64) float32
// foo happens to be of FooType, but this relationship isn't
// enforced by the compiler.
func Foo(a int, b float64) float32 {
return 2.4
}
func main() {
fmt.Printf("type of foo: %v\n", reflect.TypeOf(foo))
}
这样做的动机是我有两种类型的过滤器，可以处理文本流或结构化对象。
// 从通道处理项目
func filter1(in <-chan interface{}, out chan<- chan interface{}) {
for item := range in {
out <- doStuff(item)
}
}
// 从Scanner处理项目
func filter2(scanner *Scanner, out chan<- chan interface{}) {
for scanner.Scan() {
out <- doStuff(scanner.Text())
}
}
我希望能够编写一个函数，它接受一个*exec.Cmd和一个过滤器数组，并将它们组合起来。
英文:
If I have a type synonym FooType and a function Foo is there a way to insist that Foo is an instance of FooType. I'd like an explicit FooType so I can use it in a type switch.
I don't want to use a var and function literal if I can avoid it because then I don't get an error when I attempt to redefine a function.
package main
import (
"fmt"
"reflect"
)
type FooType func(a int, b float64) float32
// foo happens to be of FooType, but this relationship isn't
// enforced by the compiler.
func Foo(a int, b float64) float32 {
return 2.4
}
func main () {
fmt.Printf("type of foo: %v\n", reflect.TypeOf(foo))
}
The motivation for this is I have two types of filters that can process streams of text or structured objects.
// process items from channel
function filter1(in <-chan interface{}, out chan<- chan interface{}) {
for item := range in {
out <- doStuff(item)
}
}
// process items from Scanner
function filter2(scanner *Scanner, out chan<- chan interface{}) {
for scanner.Scan() {
out <- doStuff(scanner.Text())
}
}
I'd like to be able to write a function that takes an *exec.Cmd and an array of filters and combines them.
答案1
得分: 2
你可以将Foo赋值给一个匿名变量FooType，如果类型不匹配，编译器会报错，例如：
package main
type FooType func(a int, b float64) float32
func Foo(a int, b float64) float32 {
return 2.4
}
func NotAFoo(a string, b bool) float32 {
return 2.4
}
var _ FooType = Foo
var _ FooType = NotAFoo
func main() {
}
注意，var _ FooType = NotAFoo会导致错误。如果将其注释掉，程序将正常运行。Playground链接
英文:
You can assign Foo to an anonymous variable of type FooType which will the compiler will complain about if the type doesn't match, e.g.:
package main
type FooType func(a int, b float64) float32
func Foo(a int, b float64) float32 {
return 2.4
}
func NotAFoo(a string, b bool) float32 {
return 2.4
}
var _ FooType = Foo
var _ FooType = NotAFoo
func main() {
}
Note that the var _ FooType = NotAFoo blows up. If you comment it out, the program runs fine. Playground link
通过集体智慧和协作来改善编程学习和解决问题的方式。致力于成为全球开发者共同参与的知识库，让每个人都能够通过互相帮助和分享经验来进步。
评论