Dynamic call
- Go course
- Advanced
- Lesson 5/68
- 4 min
Learn to dynamically call functions and methods with reflect.
Calling a method by name
MethodByName("Name") finds a value's method by a name given as text; Call runs it. Arguments and return values travel as []reflect.Value.
m := reflect.ValueOf(h).MethodByName("Topla")
out := m.Call([]reflect.Value{reflect.ValueOf(2), reflect.ValueOf(3)})
fmt.Println(out[0].Int()) // 5Plugin systems that map command names to methods work this way.
Only exported methods
Reflect only sees methods whose names start with an upper-case letter. Also, if the method has a pointer receiver (func (h *Hesap)), you must pass reflect.ValueOf(&h).
fmt.Println(reflect.TypeOf(&h).NumMethod()) // number of exported methodsPractice Call it by name
Define type Hesap struct{} and func (Hesap) Kare(n int) int { return n * n }. Find the method with MethodByName("Kare"), Call it with argument 4 and print the result's Int().
Starter code
package main
import (
"fmt"
"reflect"
)
func main() {
// buraya yaz
}Sample solution
package main
import (
"fmt"
"reflect"
)
type Hesap struct{}
func (Hesap) Kare(n int) int { return n * n }
func main() {
m := reflect.ValueOf(Hesap{}).MethodByName("Kare")
out := m.Call([]reflect.Value{reflect.ValueOf(4)})
fmt.Println(out[0].Int())
}Expected output
16
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does <code>MethodByName</code> return if the method doesn't exist?
- An empty slice
- An invalid Value (IsValid() is false) Correct answer
- A nil error
- A compile error
Explanation: A zero Value is returned for a missing method; calling Call without checking IsValid() panics.
2 Run the method
m := reflect.ValueOf(s).MethodByName("Selam")
m.____(nil)m := reflect.ValueOf(s).MethodByName("Selam")
m.Call(nil)Explanation: Call runs the method with the given argument slice; nil can be passed when there are no arguments.
3 Dynamic call parts
| Term | Meaning |
|---|---|
MethodByName |
Finds the method by name |
Call |
Runs the method |
[]reflect.Value |
Argument and result list |
IsValid() |
Was it found? |