Go Basics

Resources: http://golang.org/

Install and Setup

sudo apt-get install golang

http://golang.org/doc/code.html discusses setting up the GOLANG environment variable and your code repository

mkdir -p $HOME/projects/go/src
export GOPATH=$HOME/projects/go (add this to .profile too)

Hello World

// hello.go
package main

import (   
    "fmt"
    "os"
    "strings"
)

func main() {
    who := "World!"  
    if len(os.Args) > 1 { /* os.Args[0] is "hello" or "hello.exe" */  
        who = strings.Join(os.Args[1:], " ")  
    }
    fmt.Println("Hello", who)  
}

Commands

godoc -http=:8000                 # host docs at http://localhost:8000
go build                          # create binary file in local directory
go install                        # create binary file in $GOPATH/bin
go run                            # just run it, disposing of binary
go get github.com/nsf/gocode      # grab a remote package and install it to $GOPATH/bin
go get -u github.com/nsf/gocode   # update to latest version of remote package

Packages

• Every file should begin with a package statement.
• A package may be defined across several files.
• Code execution begins with a main() function inside package main

Comments

// for end-of-line
/* for multiline */

Constants and Variables

count, err = fmt.Println(x) // get number of bytes printed and error
count, _ = fmt.Println(x)   // get number of bytes printed; discard error
_, err = fmt.Println(x)     // discard number of bytes printed; get error
fmt.Println(x)              // ignore return values
const limit = 512        // constant; type-compatible with any number
const top uint16 = 1421  // constant; type: uint16
start := -19             // variable; inferred type: int
end := int64(9876543210) // variable; type: int64
var i int                // variable; value 0; type: int
var debug = false        // variable; inferred type: bool
checkResults := true     // variable; inferred type: bool
stepSize := 1.5          // variable; inferred type: float64
acronym := "FOSS"        // variable; inferred type: string
i, j := 56, 67   // multiple assignment

Enumerations

const Cyan = 0     // one-per-line
const Magenta = 1
const Yellow = 2

const (            // grouped
    Cyan    = 0
    Magenta = 1
    Yellow  = 2
)

const (            // using iota
    Cyan    = iota // 0
    Magenta        // 1
    Yellow         // 2
)

type BitFlag int   // different example
const (
    Active  BitFlag = 1 << iota            // (1 << 0 == 1)
    Send    // Implicitly BitFlag = 1 << iota (1 << 1 == 2)
    Receive // Implicitly BitFlag = 1 << iota (1 << 2 == 4)
)
flag := Active | Send

Numeric type conversions

const factor = 3 // factor is compatible with any numeric type
i := 20000       // i is of type int by inference
i *= factor
j := int16(20)   // j is of type int16; same as: var j int16 = 20
i += int(j)      // Types must match so conversion is required
k := uint8(0)    // Same as: var k uint8
k = uint8(i)     // Succeeds, but k's value is truncated to 8 bits ✗
fmt.Println(i, j, k) // Prints: 60020 20 116

func Uint8FromInt(x int) (uint8, error) {
    if 0 <= x && x <= math.MaxUint8 {
        return uint8(x), nil
    }
    return 0, fmt.Errorf("%d is out of the uint8 range", x)
}

Types

Boolean

bool (true or false)

Integer

byte (synonym for uint8)
int (int32 or int64)
int8, int16, int32, int64
rune (synonym for int32)
uint (uint32 or uint64)
uint8, uint16, uint32, uint64
uintptr (uint that stores a pointer)