Go (programming language)

Go

Paradigm	compiled, concurrent, imperative, structured
Designed by	Robert Griesemer Rob Pike Ken Thompson
Developer	Google Inc.
First appeared	2009
Stable release	version 1.1.2 / 13 August 2013 (2013-08-13)
Typing discipline	strong, static
OS	Linux, Mac OS X, FreeBSD, NetBSD, OpenBSD, MS Windows, Plan 9
License	BSD-style + Patent grant
Filename extensions	.go
Website	golang.org
Major implementations
gc (8g, 6g, 5g), gccgo
Influenced by
C, Limbo, Modula, Newsqueak, Oberon, Pascal, Python

Go, sometimes referred to as golang, is an open source, compiled, garbage-collected, concurrent system programming language. It was first designed and developed at Google Inc. beginning in September 2007 by Robert Griesemer, Rob Pike, and Ken Thompson.

The language was officially announced in November 2009 and is now used in some of Google's production systems. Go's "gc" compiler targets the Linux, Mac OS X, FreeBSD, OpenBSD, Plan 9, and Microsoft Windows operating systems and the i386, amd64, and ARM processor architectures.

Description

Go is a statically-typed language with syntax loosely derived from that of C, adding automatic memory management, type and memory safety, some dynamic-typing capabilities, additional types such as variable-length arrays and key-value maps, and a large standard library. Compared to some popular languages meeting that general description, like Java and C#, Go is distinguished by:

• A syntax and environment adopting patterns more common in dynamic languages:
  • Concise variable declaration and initialization through type inference (x := 0 not int x = 0;)
  • Fast compilation times
  • Remote package management (go get)
• Distinctive approaches to particular problems
  • Built-in concurrency primitives: light-weight processes (goroutines), channels, and the select statement
  • An interface system in place of virtual inheritance
  • Compilers that, by default, produce statically linked native binaries without external dependencies
• A desire to keep the language specification simple enough to hold in a programmer's head, in part by omitting features common to similar languages:
  • No type inheritance
  • No method or operator overloading
  • No circular dependencies among packages
  • No pointer arithmetic
  • No assertions
  • No generic programming

The Go authors express an openness to generic programming, explicitly argue against assertions and pointer arithmetic, while defending the choice to omit type inheritance as giving a more useful language, encouraging heavy use of interfaces instead.

Some concurrency-related structural conventions of Go (channels and alternative channel inputs) are derived from Tony Hoare's communicating sequential processes model. Unlike previous concurrent programming languages such as occam or Limbo, Go does not provide any built-in notion of safe or verifiable concurrency.

Initially, the language did not include exception handling, but in March 2010 a mechanism known as panic/recover was implemented to handle exceptional errors while avoiding some of the problems the Go authors find with exceptions.

Interface system

In place of virtual inheritance, Go uses interfaces. An interface declaration is a list of required methods: for example, the interface io.Reader just requires the method Read(p []byte) (n int, err error). Code that uses an io.Reader could potentially read from an HTTP connection, a file, an in-memory buffer, or any other source.

Go's standard library defines interfaces for a number of concepts: input sources and output sinks, sortable collections, objects printable as strings, cryptographic hashes, and so on.

Besides calling methods via interfaces, Go allows converting interface values to other types with a run-time type check. The language constructs to do so are the type assertion, which checks against a single potential type, and the type switch, which checks against multiple types.

Go types don't declare which interfaces they implement: having the required methods is implementing the interface.

In the example below, DevZero is an io.Reader yielding an infinite stream of zeroes, like Unix /dev/zero. The main() function creates a DevZero, then passes it to the standard library's io.CopyN(io.Writer, io.Reader, int) to copy ten zero bytes to a buffer. Note that no declaration that DevZero is an io.Reader was necessary, or even possible in Go:

package main

import (
	"bytes"
	"fmt"
	"io"
)

type DevZero struct{}

func (z *DevZero) Read(p []byte) (n int, err error) {
	for i := range p {
		p[i] = 0
	}
	return len(p), nil
}

func main() {
	buffer := bytes.NewBuffer(nil)
	devZero := new(DevZero)
	// copy 10 bytes from devZero to buffer
	io.CopyN(buffer, devZero, 10)
	fmt.Println(buffer.Bytes())
}

(You can run or edit this example online.)

interface{}, the empty interface, is an important corner case because it can refer to an item of any concrete type. Code using the empty interface can't simply call methods (or built-in operators) on a referred-to object, but it can store the interface value, check if the object satisfies a more specific interface (or if it's of a specific type), or inspect it with Go's reflect package. Because interface{} can refer to any value, it's a limited way to escape the restrictions of static typing, like void* in C but with additional run-time type checks.

Go does not have interface inheritance, but one interface type can embed another; then the embedding interface requires all of the methods required by the embedded interface.

Interface values are implemented as a pointer to data and a second pointer to run-time type information. So, modifications through an interface value affect the original object, and like other pointers, interface values are nil if uninitialized. Because type information is included in the interface value, there's no type-information pointer in the underlying object, unlike in languages like Java. So, the interface system doesn't impose per-object memory overhead for objects not accessed via interface, and Go structs are stored less like Java objects and more like C structs or C# ValueTypes.

Name visibility

Visibility of structure, structure fields, variables, constants, methods, top-level types and functions outside their defining package is defined implicitly according to the capitalization of their identifier. If the identifier starts with a capital letter, the identifier is visible from outside the package.

Concurrency

Go provides goroutines, small lightweight threads; the name alludes to coroutines. Goroutines are created with the go statement from anonymous or named functions.

Goroutines are executed concurrently with other goroutines, including their caller. They do not necessarily run in separate threads, but a group of goroutines can be multiplexed onto multiple threads, allowing parallel execution. Execution control is moved between them by blocking them when sending or receiving messages over channels. Channels are bounded buffers, not network connections.

Goroutines can share data with other goroutines. Race conditions can occur in concurrent Go programs. Concurrent Go programs are not memory safe.

Implementations

There are currently two major Go compilers available for Unix variants and Windows:

• 6g/8g/5g (the compilers for AMD64, x86, and ARM respectively) with their supporting tools (collectively known as "gc") based on Thompson's previous work on Plan 9's C toolchain.
• gccgo, a GCC frontend written in C++, and now officially supported as of version 4.6, albeit not part of the standard binary for gcc.

Examples

Hello world

The following is a Hello world program in Go:

package main

import "fmt"

func main() {
    fmt.Println("Hello, World")
}

(Run or edit this example online.)

Go's automatic semicolon insertion feature requires that opening braces not be placed on their own lines, and this is thus the preferred brace style. The examples shown comply with this style.

Echo

Example illustrating how to write a program like the Unix echo command in Go:

package main

import (
    "flag"
    "fmt"
    "strings"
)

func main() {
    var omitNewline bool
    flag.BoolVar(&omitNewline, "n", false, "don't print final newline")
    flag.Parse() // Scans the arg list and sets up flags.

    str := strings.Join(flag.Args(), " ")
    if omitNewline {
        fmt.Print(str)
    } else {
        fmt.Println(str)
    }
}

Reception

Go's initial release led to much discussion.

Michele Simionato wrote in an article for artima.com:

Here I just wanted to point out the design choices about interfaces and inheritance. Such ideas are not new and it is a shame that no popular language has followed such particular route in the design space. I hope Go will become popular; if not, I hope such ideas will finally enter in a popular language, we are already 10 or 20 years too late :-(

Dave Astels at Engine Yard wrote:

Go is extremely easy to dive into. There are a minimal number of fundamental language concepts and the syntax is clean and designed to be clear and unambiguous. Go is still experimental and still a little rough around the edges.

Ars Technica interviewed Rob Pike, one of the authors of Go, and asked why a new language was needed. He replied that:

It wasn't enough to just add features to existing programming languages, because sometimes you can get more in the long run by taking things away. They wanted to start from scratch and rethink everything. ... [But they did not want] to deviate too much from what developers already knew because they wanted to avoid alienating Go's target audience.

Go was named Programming Language of the Year by the TIOBE Programming Community Index in its first year, 2009, for having a larger 12-month increase in popularity (in only 2 months, after its introduction in November) than any other language that year, and reached 13th place by January 2010, surpassing established languages like Pascal. As of March 2013, it ranked 24th in the index. Go is already in commercial use by several large organizations.

Bruce Eckel stated:

The complexity of C++ (even more complexity has been added in the new C++), and the resulting impact on productivity, is no longer justified. All the hoops that the C++ programmer had to jump through in order to use a C-compatible language make no sense anymore -- they're just a waste of time and effort. Now, Go makes much more sense for the class of problems that C++ was originally intended to solve.

Mascot

Go's mascot is a gopher designed by Renée French, who also designed Glenda, the Plan 9 Bunny. The logo and mascot are licensed under Creative Commons Attribution 3.0 license.

Naming dispute

On the day of the general release of the language, Francis McCabe, developer of the Go! programming language (note the exclamation point), requested a name change of Google's language to prevent confusion with his language. The issue was closed by a Google developer on 12 October 2010 with the custom status "Unfortunate" and with the following comment: "there are many computing products and services named Go. In the 11 months since our release, there has been minimal confusion of the two languages."

See also

• Comparison of programming languages

References

This article incorporates material from the official Go tutorial, which is licensed under the Creative Commons Attribution 3.0 license.

External links

• Official website
• A Tour of Go (official)
• Go Programming Language Resources (unofficial)
• Pike, Rob (28 April 2010). "Another Go at Language Design". Stanford EE Computer Systems Colloquium. Stanford University. (video) — A university lecture