Go's method is not same in other languages. In C++, this should not be null.
class Foo {
public:
void doSomething() {}
};
int
main() {
Foo *foo = nullptr;
foo->doSomething();
}
Go's method does not require that the receiver is instanciated.
package main
import (
"fmt"
)
type Foo struct {
}
func (f *Foo) doSomething() {
fmt.Println(f)
}
func main() {
var foo *Foo
foo.doSomething()
}
And the method hold receiver value. This is called Method Values.
package main
import (
"fmt"
)
type Foo struct {
Value string
}
func (f *Foo) WhatsUp() {
fmt.Println(f.Value)
}
func doSomething(f func()) {
f()
}
func main() {
foo := &Foo{Value: "Hello, World"}
doSomething(foo.WhatsUp)
}
The WhatsUp is evaulated with the receiver.
package main
import (
"fmt"
)
type Foo int
func (f Foo) doSomething() {
fmt.Println(f)
}
func main() {
Foo.doSomething(123)
}
So this code is valid. Foo.doSomething is the function object. It can be called with let the function object to a variable. The function type should take an first argument which is type of the receiver.
package main
import (
"fmt"
)
type Foo int
func (f Foo) doSomething() {
fmt.Println(f)
}
func main() {
var fn func(Foo)
fn = Foo.doSomething
fn(123)
}
This idiom is useful to call runtime.SetFinalizer to Close something resource must be closed.
package main
import (
"log"
"os"
"runtime"
"myresource"
)
func main() {
f := myresource.OpenSomethingMustBeClosed()
if err != nil {
log.Fatal(err)
}
runtime.SetFinalizer(f, (*myresource.Writer).Close)
}
Top comments (4)
Interesting! However, what do you mean by the words "curried function" in the title? I think
Foo.doSomethingis not curried. For example, ifdoSomethingtakes one argument,Foo.doSomething(123)causes an error.Maybe you want to say that Go can pass a receiver to a method value as an argument?
Yes, in strictly, as you think, this is not currying. The currrying is a transform taking one less argument.
Just metaphor :)
If this function object for currying, you can try this.
I never saw Go people use
Foo.doSomething(123)... Can you point to some open source projects doing this?Yes, most of cases, the function will not be called directly. As I wrote in above, it is often used as function object. See os/exec.go in Go repository.