Go (often referred to as Golang) is a high-level, general-purpose programming language that is statically typed and compiled. Originally designed in 2007 by Robert Griesemer, Rob Pike, and Ken Thompson, Go was publicly announced in November 2009, and is developed by Google and community contributors. Go has a simple syntax similar to C++, as well as garbage collection, structural typing, CSP-style concurrency, and a broad standard library.
There are two major implementations:
The original, self-hosting compiler toolchain, initially developed inside Google;
A frontend written in C++, called gofrontend, originally a GCC frontend, providing gccgo, a GCC-based Go compiler; later extended to also support LLVM, providing an LLVM-based Go compiler called gollvm.
Contents
History
Go was designed at Google in 2007 to improve programming productivity in an era of multicore, networked machines and large codebases. The designers wanted to address criticisms of other languages in use at Google, but keep their useful characteristics:
Static typing and run-time efficiency (like C)
Readability and usability (like Python)
High-performance networking and multiprocessing
Its designers were primarily motivated by their shared dislike of C++.
Go was publicly announced in November 2009, and version 1.0 was released in March 2012. Go is widely used in production at Google and in many other organizations and open-source projects.
Go developers implemented runtime support for concurrency in response to the availability of multicore systems:
Although the design of most languages concentrates on innovations in syntax, semantics, or typing, Go is focused on the software development process itself. ... The principal unusual property of the language itself—concurrency—addressed problems that arose with the proliferation of multicore CPUs in the 2010s. But more significant was the early work that established fundamentals for packaging, dependencies, build, test, deployment, and other workaday tasks of the software development world, aspects
that are not usually foremost in language design.
As of April 2022, each commit to the Go repository must be approved by two Google employees.
Branding and styling
The gopher mascot was introduced in 2009 for the open source launch of the language. Renée French, who had designed the rabbit mascot for Plan 9, adapted the gopher from an earlier WFMU T-shirt design. The gopher was originally named Gordon, but it has been nameless since 2010.
In November 2016, the Go and Go Mono fonts were released by type designers Charles Bigelow and Kris Holmes specifically for use by the Go project. Go is a humanist sans-serif resembling Lucida Grande but with near (not full) metric compatibility with Helvetica and Arial, and Go Mono is monospaced. Both fonts adhere to the WGL4 character set and were designed to be legible with a large x-height and distinct letterforms. Both Go and Go Mono adhere to the DIN 1450 standard by having a slashed zero, lowercase l with a tail, and an uppercase I with serifs.
In April 2018, the original logo was redesigned by brand designer Adam Smith. The new logo is a modern, stylized GO slanting right with trailing streamlines. The gopher mascot remained the same.
Generics
The lack of support for generic programming in initial versions of Go drew considerable criticism. The designers expressed an openness to generic programming and noted that built-in functions were in fact type-generic, but are treated as special cases; Pike called this a weakness that might be changed at some point. The Google team built at least one compiler for an experimental Go dialect with generics, but did not release it.
In August 2018, the Go principal contributors published draft designs for generic programming and error handling and asked users to submit feedback. However, the error handling proposal was eventually abandoned.
In June 2020, a new draft design document was published that would add the necessary syntax to Go for declaring generic functions and types. A code translation tool, go2go, was provided to allow users to try the new syntax, along with a generics-enabled version of the online Go Playground.
Generics were finally added to Go in version 1.18 on March 15, 2022.
Versioning
Go 1 guarantees compatibility for the language specification and major parts of the standard library. All versions up through the current Go 1.26 release have maintained this promise.
Go uses a go1.[major].[patch] versioning format, such as go1.26.0 and each major Go release is supported until there are two newer major releases. Unlike most software, Go calls the second number in a version the major, i.e., in go1.26.0 the 26 is the major version. This is because Go plans to never reach 2.0, prioritizing backwards compatibility over potential breaking changes.
Design
Go is influenced by C (especially the Plan 9 dialect), but with an emphasis on greater simplicity and safety. It consists of:
A syntax and environment adopting patterns more common in dynamic languages:
Optional concise variable declaration and initialization through type inference (x := 0 instead of var x int = 0; or var x = 0;)
Fast compilation
Remote package management (go get) and online package documentation
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, and type embedding instead of non-virtual inheritance
A toolchain that, by default, produces statically linked native binaries without external Go dependencies
A desire to keep the language specification simple enough to hold in a programmer's head, in part by omitting features that are common in similar languages.
25 reserved words
Syntax
Go's syntax includes changes from C aimed at keeping code concise and readable. A combined declaration/initialization operator was introduced that allows the programmer to write i := 3 or s := "Hello, world!", without specifying the types of variables used. This contrasts with C's int i = 3; and char *s = "Hello, world!"; (though since C23 type inference has been supported using auto, like C++). Go also removes the requirement to use parentheses in if statement conditions.
Semicolons still terminate statements; but are implicit when the end of a line occurs.
Methods may return multiple values, and returning a result, err pair is the conventional way a method indicates an error to its caller in Go. Go adds literal syntaxes for initializing struct parameters by name and for initializing maps and slices. As an alternative to C's three-statement for loop, Go's range expressions allow concise iteration over arrays, slices, strings, maps, and channels.
Go contains the following 25 keywords:
Types
Go has a number of built-in types, including numeric ones (byte, int64, float32, etc.), Booleans, and byte strings (string). Strings are immutable; built-in operators and keywords (rather than functions) provide concatenation, comparison, and UTF-8 encoding/decoding. Record types can be defined with the struct keyword.
Go contains the following primitives:
Note that byte is an alias for uint8 and rune is an alias for int32.
For each type T and each non-negative integer constant n, there is an array type denoted [n]T; arrays of differing lengths are thus of different types. Dynamic arrays are available as "slices", denoted []T for some type T (compare to other languages like C/C++ and Java, where instead the arrays are denoted T[]). These have a length and a capacity specifying when new memory needs to be allocated to expand the array. Several slices may share their underlying memory.
Pointers are available for all types, and the pointer-to-T type is denoted *T (similar to Rust; compare to other languages like C/C++ and C#, where pointers are denoted T*). Address-taking and indirection use the & and * operators, as in C, or happen implicitly through the method call or attribute access syntax. There is no pointer arithmetic, except via the special unsafe.Pointer type in the standard library.
For a pair of types K, V, the type map[K]V is the type mapping type-K keys to type-V values, which can be thought of as equivalent to Map<K, V> in other languages. The Go Programming Language specification does not give any performance guarantees or implementation requirements for map types, though it is usually implemented as a hash table (equivalent to HashMap<K, V> in other languages). Hash tables are built into the language, with special syntax and built-in functions. chan T is a channel that allows sending values of type T between concurrent Go processes.
Aside from its support for interfaces, Go's type system is nominal: the type keyword can be used to define a new named type, which is distinct from other named types that have the same layout (in the case of a struct, the same members in the same order). Some conversions between types (e.g., between the various integer types) are pre-defined and adding a new type may define additional conversions, but conversions between named types must always be invoked explicitly. For example, the type keyword can be used to define a type for IPv4 addresses, based on 32-bit unsigned integers as follows:
Package system
In Go's package system, each package has a path (e.g., "compress/bzip2" or "golang.org/x/net/html") and a name (e.g., bzip2 or html). By default other packages' definitions must always be prefixed with the other package's name. However the name used can be changed from the package name, and if imported as _, then no package prefix is required. Only the capitalized names from other packages are accessible: io.Reader is public but bzip2.reader is not. The go get command can retrieve packages stored in a remote repository and developers are encouraged to develop packages inside a base path corresponding to a source repository (such as example.com/user_name/package_name) to reduce the likelihood of name collision with future additions to the standard library or other external libraries.
Concurrency: goroutines and channels
The Go language has built-in facilities, as well as library support, for writing concurrent programs. The runtime is asynchronous: program execution that performs, for example, a network read will be suspended until data is available to process, allowing other parts of the program to perform other work. This is built into the runtime and does not require any changes in program code. The go runtime also automatically schedules concurrent operations (goroutines) across multiple CPUs; this can achieve parallelism for a properly written program.
The primary concurrency construct is the goroutine, a type of green thread. A function call prefixed with the go keyword starts a function in a new goroutine. The language specification does not specify how goroutines should be implemented, but current implementations multiplex a Go process's goroutines onto a smaller set of operating-system threads, similar to the scheduling performed in Erlang and Haskell's Glasgow Haskell Compiler (GHC) runtime implementation.
While a standard library package featuring most of the classical concurrency control structures (mutex locks, etc.) is available, idiomatic concurrent programs instead prefer channels, which send messages between goroutines. Optional buffers store messages in FIFO order and allow sending goroutines to proceed before their messages are received.
Channels are typed, so that a channel of type chan T can only be used to transfer messages of type T. Special syntax is used to operate on them; <-ch is an expression that causes the executing goroutine to block until a value comes in over the channel ch, while ch <- x sends the value x (possibly blocking until another goroutine receives the value). The built-in switch-like select statement can be used to implement non-blocking communication on multiple channels; see below for an example. Go has a memory model describing how goroutines must use channels or other operations to safely share data.
The existence of channels does not by itself set Go apart from actor model-style concurrent languages like Erlang, where messages are addressed directly to actors (corresponding to goroutines). In the actor model, channels are themselves actors, therefore addressing a channel just means to address an actor. The actor style can be simulated in Go by maintaining a one-to-one correspondence between goroutines and channels, but the language allows multiple goroutines to share a channel or a single goroutine to send and receive on multiple channels.
Binaries
The linker in the gc toolchain creates statically linked binaries by default; therefore all Go binaries include the Go runtime.
Omissions
Go deliberately omits certain features common in other languages, including (implementation) inheritance, assertions, pointer arithmetic, implicit type conversions, untagged unions, and tagged unions. The designers added only those facilities that all three agreed on.
Of the omitted language features, the designers explicitly argue against assertions and pointer arithmetic, while defending the choice to omit type inheritance as giving a more useful language, encouraging instead the use of interfaces to achieve dynamic dispatch and composition to reuse code. Composition and delegation are in fact largely automated by struct embedding; according to researchers Schmager et al., this feature "has many of the drawbacks of inheritance: it affects the public interface of objects, it is not fine-grained (i.e, no method-level control over embedding), methods of embedded objects cannot be hidden, and it is static", making it "not obvious" whether programmers will overuse it to the extent that programmers in other languages are reputed to overuse inheritance.
Exception handling was initially omitted in Go due to lack of a "design that gives value proportionate to the complexity". An exception-like panic/recover mechanism that avoids the usual try-catch control structure was proposed and released in the March 30, 2010 snapshot. The Go authors advise using it for unrecoverable errors such as those that should halt an entire program or server request, or as a shortcut to propagate errors up the stack within a package. Across package boundaries, Go includes a canonical error type, and multi-value returns using this type are the standard idiom.
Style
The Go authors put substantial effort into influencing the style of Go programs:
Indentation, spacing, and other surface-level details of code are automatically standardized by the gofmt tool. It uses tabs for indentation and blanks for alignment. Alignment assumes that an editor is using a fixed-width font. golint does additional style checks automatically, but has been deprecated and archived by the Go maintainers.
Tools and libraries distributed with Go suggest standard approaches to things like API documentation (godoc), testing (go test), building (go build), package management (go get), and so on.
Go enforces rules that are recommendations in other languages, for example banning cyclic dependencies, unused variables or imports, and implicit type conversions.
The omission of certain features (for example, functional-programming shortcuts like map and Java-style try/finally blocks) tends to encourage a particular explicit, concrete, and imperative programming style.
On day one the Go team published a collection of Go idioms, and later also collected code review comments, talks, and official blog posts to teach Go style and coding philosophy.
Tools
The main Go distribution includes tools for building, testing, and analyzing code:
go build, which builds Go binaries using only information in the source files themselves, no separate makefiles
go test, for unit testing and microbenchmarks as well as fuzzing
go fmt, for formatting code
go install, for retrieving and installing remote packages
go vet, a static analyzer looking for potential errors in code
go run, a shortcut for building and executing code
go doc, for displaying documentation
go generate, a standard way to invoke code generators
go mod, for creating a new module, adding dependencies, upgrading dependencies, etc.
go tool, for invoking developer tools (added in Go version 1.24)
It also includes profiling and debugging support, fuzzing capabilities to detect bugs, runtime instrumentation (for example, to track garbage collection pauses), and a data race detector.
Another tool maintained by the Go team but is not included in Go distributions is gopls, a language server that provides IDE features such as intelligent code completion to Language Server Protocol compatible editors.
An ecosystem of third-party tools adds to the standard distribution, such as gocode, which enables code autocompletion in many text editors, goimports, which automatically adds/removes package imports as needed, and errcheck, which detects code that might unintentionally ignore errors. A third-party source-to-source compiler, GopherJS, transpiles Go to JavaScript for front-end web development.
Examples
Hello world
where "fmt" is the package for formatted I/O, similar to C's <stdio.h> or C++ <print>.
Concurrency
The following simple program demonstrates Go's concurrency features to implement an asynchronous program. It launches two lightweight threads ("goroutines"): one waits for the user to type some text, while the other implements a timeout. The select statement waits for either of these goroutines to send a message to the main routine, and acts on the first message to arrive (example adapted from David Chisnall's book).
Testing
The testing package provides support for automated testing of go packages. Target function example:
Test code (note that assert keyword is missing in Go; tests live in <filename>_test.go at the same package):
It is possible to run tests in parallel.
Web app
The net/http package provides support for creating web applications.
This example would show "Hello world!" when localhost:8080 is visited.
Applications
Go has found widespread adoption in various domains due to its robust standard library and ease of use.
Popular applications include:
Caddy — a web server that automates the process of setting up HTTPS
Docker — a platform for containerization, aiming to ease the complexities of software development and deployment
Kubernetes — automates the deployment, scaling, and management of containerized applications
CockroachDB — a distributed SQL database engineered for scalability and strong consistency
Hugo — a static site generator that prioritizes speed and flexibility, allowing developers to create websites efficiently
TypeScript 7 is written in Go.
Reception
The interface system, and the deliberate omission of inheritance, were praised by Michele Simionato, who likened these characteristics to those of Standard ML, calling it "a shame that no popular language has followed [this] particular route".
Dave Astels at Engine Yard wrote in 2009:
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.
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. By June 2015, its ranking had dropped to below 50th in the index, placing it lower than COBOL and Fortran. But as of January 2017, its ranking had surged to 13th, indicating significant growth in popularity and adoption. Go was again awarded TIOBE Programming Language of the Year in 2016.
Bruce Eckel has 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. Go makes much more sense for the class of problems that C++ was originally intended to solve.
A 2011 evaluation of the language and its gc implementation in comparison to C++ (GCC), Java and Scala by a Google engineer found:
Go offers interesting language features, which also allow for a concise and standardized notation. The compilers for this language are still immature, which reflects in both performance and binary sizes.
Naming dispute
On November 10, 2009, 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, which he had spent 10 years developing. McCabe raised concerns that "the 'big guy' will end up steam-rollering over" him, and this concern resonated with the more than 120 developers who commented on Google's official issues thread saying they should change the name, with some even saying the issue contradicts Google's motto of: Don't be evil.
On October 12, 2010, the filed public issue ticket was closed by Google developer Russ Cox (@rsc) with the custom label "Unfortunate" accompanied by 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."
