Go (language)

Totally clueless newbie on this one.

Syntax speedrun

Variables and consts

// Assigning values to variables 
var y int = 1  // most verbose way
var y = 1      // assumes an int type, because 1 is an int literal
x := 1         // this style can be used only within a function

const x = 10 // an untyped constant declaration 
const typedX int = 10 // can only be assigned where an int is expected 

Pointers

• * is used to declare a pointer.
• & is used to get the address of a variable you’re pointing to, or want to point to.

var x int = 1
var y = &x // y holds variable x's memory address

var y *int = &x

Functions

What does a function look like in Go?

Named returns

func learnNamedReturns(x, y int) (z int) {
    z = x * y
    return
}

• z is the named return; simple assignment to it will return it.
• int is the return type.
• We just need to use return to return the named return.

Methods

Or this function, which is actually called a method, because it has a receiver, making it a function that belongs to a type:

func (c *Client) NewStack(stack *CreateStackInput) (int64, error) {
    // ...
}

• c *Client is the receiver. It’s like this in JavaScript.
• NewStack is the method name.
• stack *CreateStackInput is the argument.
• (int64, error) is the return type.

In Go, methods can be defined on either values or pointers:

• If a method is defined on a pointer (i.e. with *), it can modify the value that it points to.
• If a method is defined on a value, it receives a copy of the value, so it cannot modify the original value.

Receivers

Here is a complete piece of code that shows how a receiver is used in a method:

package main

import "fmt"

type Rectangle struct {
    Width  float64
    Height float64
}

// This method calculates the area of a Rectangle.
func (r Rectangle) Area() float64 {
    return r.Width * r.Height
}

func main() {
    rect := Rectangle{Width: 5.0, Height: 3.0}
    area := rect.Area()
    fmt.Println("Area of the rectangle:", area)
}

Testing

Ending a file’s name with _test.go tells the go test command that this file contains test functions. ¹

To run tests:

go test

# to see all of the tests and their results
go test -v 

Troubleshooting

Cannot find package

“Cannot find package github.com/…/… in any of ….” when running go get:

• Try GO111MODULE=on first.

VS Code: “Could not import…” and red underlines

• You’ve opened a Git repo in VS Code and are trying to open one of many child Go projects in that repo. VS Code / gopls is getting confused.
• In VS Code, just open the child project in its own workspace.
• Or, open your Git repo as usual, and then choose File → Add Folder to Workspace, select your module’s folder, and all will magically work!