go/doc/go_faq.html

<!-- FAQ -->

<h2 id="Origins">Origins</h2>

<h3 id="What_is_the_purpose_of_the_project">
What is the purpose of the project?</h3>

<p>
No major systems language has emerged in over a decade, but over that time
the computing landscape has changed tremendously. There are several trends:

<ul>
<li>
Computers are enormously quicker but software development is not faster.
<li>
Dependency management is a big part of software development today but the
&ldquo;header files&rdquo; of languages in the C tradition are antithetical to clean
dependency analysis&mdash;and fast compilation.
<li>
There is a growing rebellion against cumbersome type systems like those of
Java and C++, pushing people towards dynamically typed languages such as
Python and JavaScript.
<li>
Some fundamental concepts such as garbage collection and parallel computation
are not well supported by popular systems languages.
<li>
The emergence of multicore computers has generated worry and confusion.
</ul>

<p>
We believe it's worth trying again with a new language, a concurrent,
garbage-collected language with fast compilation. Regarding the points above:

<ul>
<li>
It is possible to compile a large Go program in a few seconds on a single computer.
<li>
Go provides a model for software construction that makes dependency
analysis easy and avoids much of the overhead of C-style include files and
libraries.
<li>
Go's type system has no hierarchy, so no time is spent defining the
relationships between types. Also, although Go has static types the language
attempts to make types feel lighter weight than in typical OO languages.
<li>
Go is fully garbage-collected and provides fundamental support for
concurrent execution and communication.
<li>
By its design, Go proposes an approach for the construction of system
software on multicore machines.
</ul>

<h3 id="What_is_the_origin_of_the_name">
What is the origin of the name?</h3>

<p>
&ldquo;Ogle&rdquo; would be a good name for a Go debugger.

<h3 id="What_kind_of_a_name_is_6g">
What kind of a name is 6g?</h3>

<p>
The <code>6g</code> (and <code>8g</code> and <code>5g</code>) compiler is named in the
tradition of the Plan 9 C compilers, described in
<a href="http://plan9.bell-labs.com/sys/doc/compiler.html">
http://plan9.bell-labs.com/sys/doc/compiler.html</a>
(see the table in section 2).

<code>6</code> is the architecture letter for amd64 (or x86-64, if you prefer), while
<code>g</code> stands for Go.

<h3 id="Why_not_just_write_some_libraries_for_Cpp_to_do_communication">
Why not just write some libraries for C++ to do communication?</h3>

<p>We considered doing that, but too many of the problems&mdash;lack of
garbage collection, long dependency chains, nested include files,
lack of concurrency awareness&mdash;are rooted in the design of
the C and C++ languages themselves.
We felt a viable solution required a more complete approach.

<h3 id="Why_doesnt_Go_run_on_Windows">
Why doesn't Go run on Windows yet?</h3>

<p>
We understand that a significant fraction of computers in the world
run Windows and it would be great if those computers could run Go
programs.  A group of volunteers has made significant progress toward 
porting Go to <a href="http://www.mingw.org/">MinGW</a>.
You can follow their progress at the Go Wiki's
<a href="http://code.google.com/p/go/wiki/WindowsPort">WindowsPort</a> page.
</p>

<h3 id="Whats_the_origin_of_the_mascot">
What's the origin of the mascot?</h3>

<p>
The mascot and logo were designed by
<a href="http://reneefrench.blogspot.com">Renée French</a>, who also designed
<a href="http://plan9.bell-labs.com/plan9/glenda.html">Glenda</a>,
the Plan 9 bunny.
The gopher is derived from one she used for an <a href="http://wfmu.org/">WFMU</a>
T-shirt design some years ago.
The logo and mascot are covered by the
<a href="http://creativecommons.org/licenses/by/3.0/">Creative Commons Attribution 3.0</a>
license.
</p>

<h2 id="Usage">Usage</h2>

<h3 id="Who_should_use_the_language">
Who should use the language?</h3>

<p>
Go is an experiment. We hope adventurous users will give it a try and see
if they enjoy it. Not every programmer
will, but we hope enough will find satisfaction in the approach it
offers to justify further development.

<h3 id="Is_Google_using_go_internally"> Is Google using Go
internally?</h3>

<p> The Go project was conceived to make it easier to write the kind
of servers and other software Google uses internally, but the
implementation isn't quite mature enough yet for large-scale
production use.  While we continue development we are also doing
experiments with the language as a candidate server environment.  It's
getting there.  For instance, the server behind <a
href="http://golang.org">http://golang.org</a> is a Go program; in
fact it's just the <a href="/cmd/godoc"><code>godoc</code></a> document server running in a
production configuration.


<h3 id="Do_Go_programs_link_with_Cpp_programs">
Do Go programs link with C/C++ programs?</h3>

<p>
There are two Go compiler implementations, <code>6g</code> and friends, generically called
<code>gc</code>, and <code>gccgo</code>.
<code>Gc</code> uses a different calling convention and linker and can
therefore only be linked with C programs using the same convention.
There is such a C compiler but no C++ compiler. <code>Gccgo</code> is a
GCC front-end that can, with care, be linked with GCC-compiled
C or C++ programs. However, because Go is garbage-collected it will be
unwise to do so, at least naively.

<p>
There is a &ldquo;foreign function interface&rdquo; to allow safe calling of C-written
libraries from Go code.  We expect to use SWIG to extend this capability
to C++ libraries.  There is no safe way to call Go code from C or C++ yet.

<h3 id="Does_Go_support_Google_protocol_buffers">
Does Go support Google's protocol buffers?</h3>

<p>
A separate open source project provides the necessary compiler plugin and library.
It is available at
<a href="http://code.google.com/p/goprotobuf/">http://code.google.com/p/goprotobuf/</a>
</p>

<h3 id="Can_I_translate_the_Go_home_page">
Can I translate the Go home page into another language?</h3>

<p>
Absolutely. We encourage developers to make Go Language sites in their own languages.
However, if you choose to add the Google logo or branding to your site
(it does not appear on <a href="http://golang.org/">golang.org</a>),
you will need to abide by the guidelines at
<a href="http://www.google.com/permissions/guidelines.html">http://www.google.com/permissions/guidelines.html</a>
</p>

<h2 id="Design">Design</h2>

<h3 id="Why_doesnt_Go_have_feature_X">Why doesn't Go have feature X?</h3>

<p>
Every language contains novel features and omits someone's favorite
feature. Go was designed with an eye on felicity of programming, speed of
compilation, orthogonality of concepts, and the need to support features
such as concurrency and garbage collection. Your favorite feature may be
missing because it doesn't fit, because it affects compilation speed or
clarity of design, or because it would make the fundamental system model
too difficult.

<p>
If it bothers you that Go is missing feature <var>X</var>,
please forgive us and investigate the features that Go does have. You might find that
they compensate in interesting ways for the lack of <var>X</var>.

<h3 id="Why_is_the_syntax_so_different_from_Cpp">
Why is the syntax so different from C++?</h3>

<p>
This and other language design questions are answered in
the separate <a href="go_lang_faq.html">language design FAQ</a>.

<h2 id="Object_Oriented_Programming">
Object-Oriented Programming</h2>

<h3 id="Is_Go_an_object-oriented_language">
Is Go an object-oriented language?</h3>

<p>
Yes and no. Although Go has types and methods and allows an
object-oriented style of programming, there is no type hierarchy.
The concept of &ldquo;interface&rdquo; in Go provides a different approach that
we believe is easy to use and in some ways more general. There are
also ways to embed types in other types to provide something
analogous&mdash;but not identical&mdash;to subclassing.
Moreover, methods in Go are more general than in C++ or Java:
they can be defined for any sort of data, not just structs.

<p>
Also, the lack of type hierarchy makes &ldquo;objects&rdquo; in Go feel much more
lightweight than in languages such as C++ or Java.

<h3 id="How_do_I_get_dynamic_dispatch_of_methods">
How do I get dynamic dispatch of methods?</h3>

<p>
The only way to have dynamically dispatched methods is through an
interface. Methods on structs or other types are always resolved statically.


<h2 id="Writing_Code">Writing Code</h2>

<h3 id="How_are_libraries_documented">
How are libraries documented?</h3>

<p>
There is a program, <code>godoc</code>, written in Go, that extracts
package documentation from the source code. It can be used on the
command line or on the web. An instance is running at
<a href="http://golang.org/pkg/">http://golang.org/pkg/</a>.
In fact, <code>godoc</code> implements the full site at
<a href="http://golang.org/">http://golang.org/</a>.

<h3 id="Is_there_a_Go_programming_style_guide">
Is there a Go programming style guide?</h3>

<p>
Eventually, there may be a small number of rules to guide things
like naming, layout, and file organization.
The document <a href="effective_go.html">Effective Go</a>
contains some style advice.
More directly, the program <code>gofmt</code> is a pretty-printer
whose purpose is to enforce layout rules; it replaces the usual
compendium of do's and don'ts that allows interpretation.
All the Go code in the repository has been run through <code>gofmt</code>.

<h3 id="How_do_I_submit_patches_to_the_Go_libraries">
How do I submit patches to the Go libraries?</h3>

<p>
The library sources are in <code>go/src/pkg</code>.
If you want to make a significant change, please discuss on the mailing list before embarking.

<p>
See the document
<a href="contribute.html">Contributing to the Go project</a>
for more information about how to proceed.

<h3 id="Where_is_assert">
Where is assert?</h3>

<p>
Go doesn't provide assertions. They are undeniably convenient, but our
experience has been that programmers use them as a crutch to avoid thinking
about proper error handling and reporting. Proper error handling means that
servers continue operation after non-fatal errors instead of crashing.
Proper error reporting means that errors are direct and to the point,
saving the programmer from interpreting a large crash trace. Precise
errors are particularly important when the programmer seeing the errors is
not familiar with the code.

<p>
The same arguments apply to the use of <code>assert()</code> in test programs. Proper
error handling means letting other tests run after one has failed, so
that the person debugging the failure gets a complete picture of what is
wrong. It is more useful for a test to report that
<code>isPrime</code> gives the wrong answer for 2, 3, 5, and 7 (or for
2, 4, 8, and 16) than to report that <code>isPrime</code> gives the wrong
answer for 2 and therefore no more tests were run. The programmer who
triggers the test failure may not be familiar with the code that fails.
Time invested writing a good error message now pays off later when the
test breaks.

<p>
In testing, if the amount of extra code required to write
good errors seems repetitive and overwhelming, it might work better as a
table-driven test instead.
Go has excellent support for data structure literals.

<p>
We understand that this is a point of contention. There are many things in
the Go language and libraries that differ from modern practices, simply
because we feel it's sometimes worth trying a different approach.

<h2 id="Implementation">Implementation</h2>

<h3 id="What_compiler_technology_is_used_to_build_the_compilers">
What compiler technology is used to build the compilers?</h3>

<p>
<code>Gccgo</code> has a C++ front-end with a recursive descent parser coupled to the
standard GCC back end. <code>Gc</code> is written in C using
<code>yacc</code>/<code>bison</code> for the parser.
Although it's a new program, it fits in the Plan 9 C compiler suite
(<a href="http://plan9.bell-labs.com/sys/doc/compiler.html">http://plan9.bell-labs.com/sys/doc/compiler.html</a>)
and uses a variant of the Plan 9 loader to generate ELF binaries.

<p>
We considered writing <code>6g</code>, the original Go compiler, in Go itself but
elected not to do so because of the difficulties of bootstrapping and
especially of open source distribution&mdash;you'd need a Go compiler to
set up a Go environment. <code>Gccgo</code>, which came later, makes it possible to
consider writing a compiler in Go, which might well happen. (Go would be a
fine language in which to implement a compiler; a native lexer and
parser are already available in <a href="/pkg/go/"><code>/pkg/go</code></a>.)

<p>
We also considered using LLVM for <code>6g</code> but we felt it was too large and
slow to meet our performance goals.

<h3 id="How_is_the_runtime_implemented">
How is the runtime implemented?</h3>

<p>
Again due to bootstrapping issues, the runtime is mostly in C (with a
tiny bit of assembler) although Go is capable of implementing most of
it now. <code>Gccgo</code>'s runtime uses <code>glibc</code>.
<code>Gc</code> uses a custom library, to keep the footprint under
control; it is
compiled with a version of the Plan 9 C compiler that supports
segmented stacks for goroutines.
Work is underway to provide the same stack management in
<code>gccgo</code>.

<h2 id="Performance">Performance</h2>

<h3 id="Why_does_Go_perform_badly_on_benchmark_x">
Why does Go perform badly on benchmark X?</h3>

<p>
One of Go's design goals is to approach the performance of C for comparable
programs, yet on some benchmarks it does quite poorly, including several 
in <a href="/test/bench/">test/bench</a>. The slowest depend on libraries 
for which versions of comparable performance are not available in Go. 
For instance, pidigits depends on a multi-precision math package, and the C
versions, unlike Go's, use <a href="http://gmplib.org/">GMP</a> (which is
written in optimized assembler). 
Benchmarks that depend on regular expressions (regex-dna, for instance) are
essentially comparing Go's stopgap <a href="/pkg/regexp">regexp package</a> to
mature, highly optimized regular expression libraries like PCRE.
</p>

<p>
Benchmark games are won by extensive tuning and the Go versions of most
of the benchmarks need attention.  If you measure comparable C
and Go programs (reverse-complement is one example), you'll see the two
languages are much closer in raw performance than this suite would
indicate.
</p>

<p>
Still, there is room for improvement. The compilers are good but could be
better, many libraries need major performance work, and the garbage collector
isn't fast enough yet (even if it were, taking care not to generate unnecessary 
garbage can have a huge effect).
</p>