Tag Archives: programming languages

Notes on Go, part 7 of ∞

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Coming to Go from Ruby has been an experience and a half. A lot of the things I’ve stubbed my toes on are either vocabulary things, or things that I don’t know about because I’ve never really used a statically typed language before.

A map is a hash table is a ruby hash

Lets start by paying a visit to Wikipedia, the repository of all modern knowledge.

Default values are unexpected

In Go, some types have a default value (probably to deal with the whole static typing thing???). For example, the default value of a boolean is false.

Similarly, ints also have a default value of 0.

So if I initialize a map of strings and ints, I get a number back, even if that key doesn’t exist in the map.

Multiple returns strike again

To solve the default value problem, Go offers optional multiple returns when querying a map/hash.

Now, when I query the map, I can then check the value of ok, which will return false if the key didn’t actually exist in the map.

The multiple return collection is optional. If I remove the ok assignment, Go will not complain.

make() vs literal syntax

There are two ways to initialize a map. You can use the make() syntax:

Or you can use the ‘literal’ syntax, which I’ve used the the previous examples. Arbitrarily, I like the literal syntax. Maybe I just like curly braces.

Resources

A Tour of Go
Go maps in action
Go By Example
Effective Go

Notes on Go, part 4 of ∞

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I learned a fun thing about the html/template package in Go. When compiling your program, it does not check the validity of your template.

I was working through the Writing Web Applications tutorial, and I made the following mistake:

<h1>{{.Title</h1>

There is supposed to be a set of closing brackets after Title.

<h1>{{.Title}}</h1>

However, when I compiled and ran my program, I didn’t get any error messages until I tried to access /view/test. Then, it blew up with a panic message. Reading through the stack trace pretty quickly implicated the Template package, and it was a relatively quick problem to solve.

Notes on Go, part 3 of ∞

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Here are my notes on how multiple returns work.

package main

import &quot;fmt&quot;

func split(sum int) (x, y int) {
    x = sum * 4 / 9
    y = sum - x
    return
}

func main() {
    results := split(17)
    fmt.Println(results)
    fmt.Println(split(17))
}

Returns prog.go:12: multiple-value split() in single-value context (Check it out on the Go Playground)

package main

import &quot;fmt&quot;

func split(sum int) (x, y int) {
    x = sum * 4 / 9
    y = sum - x
    return
}

func main() {
    resultsx, resultsy := split(17)
    fmt.Println(resultsx)
    fmt.Println(resultsy)
    fmt.Println(split(17))
}

Returns:

7
10
7 10

(Check it out on the Go Playground)

If a function returns multiple things, you are required to give each of those things a name if you are going to save them to a variable. The exception (so far) is if you directly pass the function to another function that can handle that sort of thing.

If you don’t want to save one of the returns, you can assign it to _, which basically says ‘I know there is going to be something here, throw it out immediately’.

Notes on Go, part 2 of ∞

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Why aren’t my test running?

The command go test will only pick up tests in the directory that the command is being run in. To have it find tests in sub-folders, try the command go test ./.... This searches recursively through the sub-folders and finds the hiding tests and runs them.

Tests still aren’t running? If you are using godep to manage dependancies, you can try:

godep get

Still getting error messages á la:

somefolder/some_test.go:10:2: cannot find package &quot;github.com/THING/code&quot; in any of:
    /usr/local/Cellar/go/1.5.1/libexec/src/github.com/THING/code (from $GOROOT)
    ~/code/go/src/github.com/THING/code (from $GOPATH)

Try the following series of commands from the root directory of your project.

godep restore
rm -rf Godeps
godep save ./...
godep go test ./...
go test ./...

Stay tuned for an actual explanation of why any of this works when I figure it out!

Notes on Go, part 1 of ∞

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When writing tests in Go, there are a few useful ways to get info printed out to the screen.

  • t.log

Inside the test, you can log stuff using t.log. This will only show up if you use the -v flag when running go test.

  • fmt.PrintLn

Inside the actual program itself, you can print things using an fmt.Print command, and running the tests with the -v flag.

Basically, the -v flag is your friend when you want to see things in your go tests!