Learning Golang, Day 10 – Type Assertions, Type Switches, and Stringers.

Mon, May 23, 2022 Estimated reading time: 3 minutes.

Here we are on day 10. Today I read about and played with Type Assertions, Type Switches, and Stringers in Go.

I enjoyed the session, as it, on the whole, made sense. Type assertions and switches were pretty self-explanatory, and something that I look forward to using. The same goes for Stringers, which remind me a lot of PHP’s magic __toString function.

Because of that comparison, they’re what I want to focus on for just a bit. From what I understand, to implement a Stringer, all you have to do is to add a method to a Type in Go named String that returns a string.

In PHP, if a class implements the __toString method, which returns a string, then the object can be used as a string. Here’s an example to demonstrate what I’m talking about.

<?php

class User
{
    public function __construct(protected string $firstName, protected string $lastName){}

    public function __toString(): string {
        return sprintf("%s %s", $this->firstName, $this->lastName);
    }
}

$user = new User("Matthew", "Setter");
echo $user;

In this example, when the code is run, the string "Matthew Setter" will be printed to the terminal.

However, when I started working through the Stringers exercise, things started to come undone. You can see the sample code below.

package main

import "fmt"

type IPAddr [4]byte

// TODO: Add a "String() string" method to IPAddr.

func main() {
	hosts := map[string]IPAddr{
		"loopback":  {127, 0, 0, 1},
		"googleDNS": {8, 8, 8, 8},
	}
	for name, ip := range hosts {
		fmt.Printf("%v: %v\n", name, ip)
	}
}

I looked at the example and thought that I’d just have to create a String() method with a pointer receiver to the IPAddr type, that:

Converted the byte array to a string or array of strings
Joined the string array together into a single string, where each element was separated by a dot/period, as in the example below
Returned the string

func (ipa IPAddr) String() string {
	var output []string
	for _, v := range ipa {
		output = append(output, string(v))
	}

	return strings.Join(output, ".")
}

That didn’t work, as it converted the byte values to strings, not a string representation of the byte’s value I don’t know if I explained that correctly. What I mean is that, for example, it converted 127 to the DEL char, and 0 to the NULL char, instead of converting 127 to "127" and 0 to "0", etc. I hope that makes sense.

I kept playing further but didn’t really make a lot of progress. To try and get "unstuck", I asked a question in the newbies channel in gophers.slack.com and am currently having a discussion about it. I hope to work through this and, in tomorrow’s session, be able to solve the exercise.

What’s more, I am happy for having gotten stuck, as it’s helped me to start to appreciate a wider array of types that I’d been used to for quite some time now.

See you, tomorrow!

#learninggolang

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Learning Golang, Day 10 – Type Assertions, Type Switches, and Stringers.

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