This is a Go function for print debugging, where all the printed statements go to a dedicated file.

The module exports a single function Q(), which you can pass any expression, and it will be logged to the file /tmp/q.txt. This means you can log from any goroutine or process, and you can easily find any q-printed statements separate from the rest of your logging.

Here's a simple example:

f, err := os.Stat("maybe_this_file_exists.txt")
q.Q(err)

If the first argument is a format string, then the string will be interpolated before it gets logged. For example:

name := "triangle"
sides := 3

q.Q("a %s has %d sides", name, sides)
// "a triangle has 3 sides"

As well as logging the value, Q() logs the name of the calling function, and the expression that you logged. For example, Q(2 + 2) will be logged as main: 2 + 2 = 4.

Here's a longer example of a program that uses Q():

package main

import (
	"github.com/alexwlchan/q"
	"os"
)

func printShapeInfo(name string, sides int) {
	q.Q("a %s has %d sides", name, sides)
}

func main() {
	q.Q("hello world")

	q.Q(2 + 2)

	_, err := os.Stat("does_not_exist.txt")
	q.Q(err)

	printShapeInfo("triangle", 3)
}

And here's what gets written to /tmp/q.txt:

$ cat /tmp/q.txt
main: "hello world"

main: 2 + 2 = 4

main: err = stat does_not_exist.txt: no such file or directory

printShapeInfo: a triangle has 3 sides

0. Read the file q.go and make sure you're happy with what it's doing. It's barely a hundred lines of code. Make sure I'm not secretly sending all your logs to my web server!

1. Clone this repo:

   $ git clone https://github.com/alexwlchan/q.go.git ~/repos/q

2. Create a directory q in the root of the project where you want to use this code, and symlink q.go from your checkout:

   $ mkdir q
   $ ln -s ~/repos/q/q.go q/q.go

3. Add the q.go file to your .git/info/exclude file, so it will be ignored by Git:

   $ echo q.go >> .git/info/exclude

This final step allows you to use q in your project, without affecting your coworkers: you don't need to add an entry to your checked in .gitignore or add it to the list of project dependencies. It also means you can't check in any leftover debugging code with q, because your tests in CI will immediately fail to compile.