Using callbacks and functions as a type in go

Question

I am attempting to create a sort of function that is similar to the Express (NodeJS) route method in Go:

app.get("route/here/", func(req, res){
    res.DoStuff()
});

In this example I want "foo" (the type) to be the same as the anonymous function in the above method. Here is one of my failed attempts using Go:

type foo func(string, string)

func bar(route string, io foo) {
        log.Printf("I am inside of bar")
        // run io, maybe io() or io(param, param)?
}

func main() {
        bar("Hello", func(arg1, arg2) {
                return  arg + arg2
        })
}

How might I fix my dilemma? Should I not use a type and use something else? What are my options?

Side note but probably related - In terms of cool Go web frameworks that use a middleware pattern with a general syntax that might be familiar to Express is echo.labstack.com. — syllabix
– syllabix, Commented Oct 4, 2016 at 2:14

syllabix · Accepted Answer · 2021-05-10 07:58:13Z

15

You are on the right track - creating a type for a func in the context you are using it adds clearer design intent and additional type safety.

You just need to modify your example a bit for it to compile:

package main

import "log"

//the return type of the func is part of its overall type definition - specify string as it's return type to comply with example you have above
type foo func(string, string) string

func bar(route string, io foo) {

    log.Printf("I am inside of bar")
    response := io("param", "param")
    log.Println(response)

}

func main() {

    bar("Hello", func(arg1, arg2 string) string {
        return arg1 + arg2
    })

}

edited May 10, 2021 at 7:58

answered Oct 4, 2016 at 2:45

syllabix

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Paco Preciado Mendoza · Accepted Answer · 2019-04-14 18:50:18Z

1

package main

import (
    "fmt"
    "log"
)

type foo func(string, string)

func bar(route string, callback foo) bool {
 //...logic

  /* you can return the callback to use the 
     parameters and also in the same way you 
     could verify the bar function
   */
    callback("param", "param")
    return true
}

func main() {
    fmt.Println("Hello, playground")

    res := bar("Hello", func(arg1, arg2 string) {
        log.Println(arg1 + "_1")
        log.Println(arg2 + "_2")
    })

    fmt.Println("bar func res: ", res)
}

answered Apr 14, 2019 at 18:50

Paco Preciado Mendoza

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