Call a Struct and its Method by name in Go?
To call a method on an object, first use reflect.ValueOf
. Then find the method by name, and then finally call the found method. For example:
package main
import "fmt"
import "reflect"
type T struct {}
func (t *T) Foo() {
fmt.Println("foo")
}
func main() {
var t T
reflect.ValueOf(&t).MethodByName("Foo").Call([]reflect.Value{})
}
type YourT1 struct {}
func (y YourT1) MethodBar() {
//do something
}
type YourT2 struct {}
func (y YourT2) MethodFoo(i int, oo string) {
//do something
}
func Invoke(any interface{}, name string, args... interface{}) {
inputs := make([]reflect.Value, len(args))
for i, _ := range args {
inputs[i] = reflect.ValueOf(args[i])
}
reflect.ValueOf(any).MethodByName(name).Call(inputs)
}
func main() {
Invoke(YourT2{}, "MethodFoo", 10, "abc")
Invoke(YourT1{}, "MethodBar")
}
Really the code needs to check the method's input number and even whether the method itself exists.
You can reference this http://gowalker.org/reflect#Type
- Check "any" is a struct type
- Check "any" has "name" method
- Check the number of method "name" input parameters is equal the length of args
- Implement
ret
byreflect.Value.Interface()
and be careful the Ptr type;
Or you can use SomeInterface{}
instead of directly using interface{}
to ensure this "any" type, like this:
type Shape interface {
Area() float64 //some method to ensure any is an Shape type.
}
func Invoke(s Shape, name string, inputs...interface{}) []interface{} {
}
so this is OK
color := Invoke(Circle{}, "GetColor")[0].(Color)
but
Invoke(NotAShape{}, "ForBar")
can't be compiled because NotAnShape
isn't a Shape.
If you can't be sure about the first type at compile time, you can build a map to store all possible type, like this:
map[string]reflect.Value{
"YourT1" : reflect.ValueOf(YourT1{})
"YourT2" : reflect.ValueOf(YourT2{})
"Circle" : reflect.ValueOf(Cirlce{}) // or reflect.ValueOf(&Circle{})
}
gist invoke struct method with error handling
// Invoke - firstResult, err := Invoke(AnyStructInterface, MethodName, Params...)
func invoke(any interface{}, name string, args ...interface{}) (reflect.Value, error) {
method := reflect.ValueOf(any).MethodByName(name)
methodType := method.Type()
numIn := methodType.NumIn()
if numIn > len(args) {
return reflect.ValueOf(nil), fmt.Errorf("Method %s must have minimum %d params. Have %d", name, numIn, len(args))
}
if numIn != len(args) && !methodType.IsVariadic() {
return reflect.ValueOf(nil), fmt.Errorf("Method %s must have %d params. Have %d", name, numIn, len(args))
}
in := make([]reflect.Value, len(args))
for i := 0; i < len(args); i++ {
var inType reflect.Type
if methodType.IsVariadic() && i >= numIn-1 {
inType = methodType.In(numIn - 1).Elem()
} else {
inType = methodType.In(i)
}
argValue := reflect.ValueOf(args[i])
if !argValue.IsValid() {
return reflect.ValueOf(nil), fmt.Errorf("Method %s. Param[%d] must be %s. Have %s", name, i, inType, argValue.String())
}
argType := argValue.Type()
if argType.ConvertibleTo(inType) {
in[i] = argValue.Convert(inType)
} else {
return reflect.ValueOf(nil), fmt.Errorf("Method %s. Param[%d] must be %s. Have %s", name, i, inType, argType)
}
}
return method.Call(in)[0], nil
}