Plugin symbol

Learn to get an exported symbol with Lookup.

Using the symbol

The result of Lookup is a plugin.Symbol. For a function you type-assert to the function type; for a variable, to a pointer to its type:

selam := sym.(func(string) string)
fmt.Println(selam("Ada"))

surum := vsym.(*string)  // pointer for a variable
fmt.Println(*surum)

A contract through interfaces

A tidier approach: the plugin exports a value that satisfies an interface and the main program asserts to that interface. The interface is defined in a shared package:

type Komut interface { Calistir() string }

k := sym.(Komut)
fmt.Println(k.Calistir())

Exercise Type assertion

Declare var sym any = func(n int) int { return n + 1 } to imitate a plugin symbol. Convert it with sym.(func(int) int) and print f(9).

Show example solution

package main

import "fmt"

func main() {
    var sym any = func(n int) int { return n + 1 }
    f := sym.(func(int) int)
    fmt.Println(f(9))
}

Test yourself

If the plugin has <code>var Surum = "1.0"</code>, which type is the Lookup result asserted to?
- string
- func() string
- []byte
- *string
Show answer

*string — Variable symbols come back as pointers, so the main program can read and change the variable.

Convert to a function

f := sym.(____)
fmt.Println(f(3))

Show answer

f := sym.(func(int) int)
fmt.Println(f(3))

Symbol and assertion

func Selam(string) string

func(string) string
var Surum string

*string
var Sayac int

*int
var Eklenti Komut

The Komut interface

Next lesson: Plugin and error

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