Go lang at eweek.com and stanford.edu

10.7.30: news.adda/lang"go

. Go is a systems programming language
expressive, concurrent, garbage-collected
. go @ g'code .
. go @ golang.org .

7.30: news.adda/lang"go/eweek's interview of Pike:

paraphrase of eweek.com` Darryl K. Taft 2009-11-13
Pike, Thompson, and Griesemer
are the designers; and,
eweek is interviewing Pike .

. it can take a very long time
to build a program.
Even incremental builds can be slow.
. many of the reasons for that are
just C and C++, and the tools
that everybody used were also slow.
So we wanted to start from scratch .

[. unusual design based on the
Plan 9 compiler suite
Gccgo, written in C++,
generates good code more slowly]
The Plan 9 team produced some
programming languages of its own,
such as Alef and Limbo,
-- in the same family tree
and inspired by the same approach."
... it uses the Plan 9 compiler suite,
linker and assembler,
but the Go compiler is all new.

. One of the big problems is
maintaining the dependencies;
C++ and C in particular
make it very hard to guarantee
that you're not building
anything that you don't need to.
it's the almost dominant reason
why build times are so slow
for large C++ applications.
. Go is very rigid about
dependency specification;
go warns if you try to
pull in an unused dependency .
This guarantees a minimal tree
and that really helps the build.
. we pull the dependency information
up the tree as we go
so that everything
is looked at only once.
and never compiled more than once .
. the typically used lang's
nowadays {C++, Java},
were designed a generation ago
in terms of programming abilities
and understanding.
And they're not aging very well
in the advent of multicore processing
and the dominance of cluster computing
-- things like that really needed a
rethink at the language level.

an unusual type system:
. some have described Go as
oop without objects.
Instead of having a notion of a class
defining all the methods for that class
and then subclassing and so on,
Go is much more orthogonal .
. to write a program that needs
something like a 'write' or a 'sort'
you just say I need something that
knows how to write or sort.
You don't have to explicitly
subclass something from a sorting interface
and build it down.

It's much more compiler-derived
instead of programmer-specified.
And a smaller point,
but it matters to some of us:
you can put an oop`method,
in any type in the system.
it is fully statically typed;
eg, At compile time you know
that everything coming in
can implement the sorting interface
or it would not statically compile .

"But there is dynamic type information
under the covers ...
So it's a statically typed language
with a little bit of
polymorphism mixed in.

Go supports concurrency:
Although most of today's larger machines
have multiple cores,
the common languages out there
don't really have enough support
for using those cores efficiently .

. there are libraries to help with this,
"but they're very difficult to use
and the primitives are fairly clumsy,"

"One of our goals in Go
was to make a language that
could use those processors well,
particularly for the kind of
server-side programming
that is done at Google:
where you have many client requests
coming into a machine
that's multiplexing them .
"It's a parallel Web server with
multiple internal threads of control
for each client request that comes in"

We don't yet have the build
at the kind of scale we need
to say Go is definitely the way to go.
And there's definitely
some more library support needed
for things like scheduling and so on.
But from a starting point
it's a really good place to be."

. programmers who are used to developing
systems software with {C, C++, Java}
will find Go interesting because
it's not much slower than C
and, has a lot of the
nice, light dynamic feel
of those [rapid-dev lang's];
eg, {Python, Ruby (JavaScript?)}

"It's not a Google official language
the way that, say,
Java was an official Sun language,"

a skunkworks project:
"(. one typically developed by a
small and loosely structured group
who research and develop
primarily for the sake of radical innovation.
A skunkworks project often operates with
a high degree of autonomy, in secret,
and unhampered by bureaucracy,
with the understanding that
if the development is successful
then the product will be designed later
according to the usual process.)
. we want people to help us expand it
esp'ly the Windows support; and tools:
esp'ly a debugger, and an IDE;
esp'ly Eclipse support:
It's a fair bit of effort
to make a proper plug-in for Eclipse.

. a few welcomed language features,
like union types, are still needed .

The run-time needs a fair bit of development.
The garbage collector works just fine
but it's not robust or efficient enough
to be a practical solution
for a large-scale server.
. we're very aware of the need to
prevent gc causing pauses
in real-time systems programming .
But there's some very clever work
published at IBM that may be of use
for a much better garbage collector.
. that would be a milestone:
a native compiled language with gc
that works well in a systems environment.

news.adda/lang"go/Another Go at Language Design:

Google's Rob Pike speaking at stanford.edu 2010.4.28
Stanford EE Computer Systems Colloquium

About the talk:
. A while back, it seemed that
type-driven object-oriented languages
such as C++ and Java had taken over.
They still dominate education.
Yet the last few years
have seen a number of
different languages reach prominence,
often of very different styles:
Python, Ruby, Scala, Erlang, Lua,
and many more.
Surely there are enough languages.
Yet new ones keep appearing.
Why? And why now?
In this talk I will explain
some possible reasons
and why they led us to define
yet another language, Go.
Slides: (pdf) [the source of this entry]

Another Go at Language Design:
Russ Cox
Robert Griesemer
Rob Pike
Ian Taylor
Ken Thompson
David Symonds, Nigel Tao, Andrew
Gerrand, Stephen Ma, and others,
many contributions from the
open source community.
I'm always delighted by the
light touch and stillness
of early programming languages.
Not much text; a lot gets done.
Old programs read like quiet conversations
between a well-spoken research worker
and a well-studied mechanical colleague,
not as a debate with a compiler.
Who'd have guessed
sophistication bought such noise?
-Dick Gabriel

If more than one function is selected,
any function template specializations
in the set
are eliminated if the set also contains
a non-template function,
and any given
function template specialization F1
is eliminated if the set contains
a second function template specialization
whose function template
is more specialized than the
function template of F1
according to the
partial ordering rules of
After such eliminations, if any,
there shall remain exactly one selected function.
(C++0x, §13.4 [4])

Which Boost templated pointer type should I use?

public static <I, O> ListenableFuture<O>
  ListenableFuture<I> input
  , Function <? super I, ? extends ListenableFuture
      <? extends O
dear god make it stop
- a recently observed chat status

foo::Foo *myFoo =
new foo::Foo(foo::FOO_INIT)
- but in the original Foo was a longer word

How did we get here?
A personal analysis:
1) C and Unix became dominant in research.
2) The desire for a higher-level language
led to C++,
which grafted the Simula style of oop onto C.
It was a poor fit
but since it compiled to C
it brought high-level programming to Unix.
3) C++ became the language of choice
in {parts of industry, many research universities}.
4) Java arose
as a clearer, stripped-down C++.
5) By the late 1990s,
a teaching language was needed that seemed relevant,
and Java was chosen.
Programming became too hard
These languages are hard to use.
They are subtle, intricate, and verbose.
Their standard model is oversold,
and we respond with add-on models
such as "patterns".
( Norvig:
patterns are a demonstration of
weakness in a language.
Yet these languages are successful and vital.
A reaction
The inherent clumsiness of the main languages
has caused a reaction.
A number of successful simpler languages
(Python, Ruby, Lua, JavaScript, Erlang, ...)
have become popular, in part,
as a rejection of the standard languages.
Some beautiful and rigorous languages
(Scala, Haskell, ...)
were designed by domain experts
although they are not as widely adopted.
So despite the standard model,
other approaches are popular
and there are signs of a growth in
"outsider" languages,
a renaissance of language invention.
A confusion
The standard languages (Java, C++)
are statically typed.
Most outsider languages (Ruby, Python, JavaScript)
are interpreted and dynamically typed.
Perhaps as a result, non-expert programmers
have confused "ease of use" with
interpretation and dynamic typing.
This confusion arose because of
how we got here:
grafting an orthodoxy onto a language
that couldn't support it cleanly.
standard languages#The good:
very strong:
type-safe, effective, efficient.
In the hands of experts? great.
Huge systems and huge companies
are built on them.
. practically work well for
large scale programming:
big programs, many programmers.
standard languages#The bad:
hard to use.
Compilers are slow and fussy.
Binaries are huge.
Effective work needs language-aware tools,
distributed compilation farms, ...
Many programmers prefer to avoid them.
The languages are at least 10 years old
and poorly adapted to the current tech:
clouds of networked multicore CPUs.
Flight to the suburbs:
This is partly why Python et al.
have become so popular:
They don't have much of the "bad".
- dynamically typed (fewer noisy keystrokes)
- interpreted (no compiler to wait for)
- good tools (interpreters make things easier)
But they also don't have the "good":
- slow
- not type-safe (static errors occur at runtime)
- very poor at scale
And they're also not very modern.
A niche
There is a niche to be filled:
a language that has the good,
avoids the bad,
and is suitable to modern computing infrastructure:
statically typed
light on the page
fast to work in
scales well
doesn't require tools, but supports them well
good at networking and multiprocessing
The target:
Go aims to combine the safety and performance
of a statically typed compiled language
with the expressiveness and convenience
of a dynamically typed interpreted language.
. be suitable for modern systems programming.
Hello, world 2.0
Serving http://localhost:8080/world:
package main
import ( "fmt" "http" )
func handler(c *http.Conn, r *http.Request)
{ fmt.Fprintf(c, "Hello, %s.", r.URL.Path[1:]) }
func main()
{ http.ListenAndServe
(":8080", http.HandlerFunc(handler)) }
How does Go fill the niche?
Fast compilation
Expressive type system
Garbage collection
Systems programming capabilities
Clarity and orthogonality
Compilation demo:
Why so fast?
New clean compiler worth ~5X compared to gcc.
We want a millionX for large programs,
so we need to fix the dependency problem.
In Go, programs compile into packages
and each compiled package file
imports transitive dependency info.
If [depends on](A.go, B.go, C.go}:
- compile C.go, B.go, then A.go.
- to compile A.go,
compiler reads B.o but not C.o.
At scale, this can be a huge speedup.
Trim the tree:
Large C++ programs (Firefox, OpenOffice, Chromium)
have huge build times.
On a Mac (OS X 10.5.7, gcc 4.0.1):
. C`stdio.h: 00,360 lines from 9 files
C++`iostream: 25,326 lines from 131 files
Obj'C`Cocoa.h 112,047 lines from 689 files
-- But we haven't done any real work yet!
Go`fmt: 195 lines from 1 file:
summarizing 6 dependent packages.
As we scale,
the improvement becomes exponential.
Wednesday, April 28, 2010
Expressive type system
Go is an oop language, but unusually so.
There is no such thing as a class.
There is no subclassing.
. even basic types, eg,{integers, strings},
can have methods.
Objects implicitly satisfy interfaces,
which are just sets of methods.
Any named type can have methods:
type Day int
var dayName = []string{"Sunday", "Monday", [...]} 
func (d Day) String() string
{ if 0 <= d && int(d) < len(dayName)
    { return dayName[d] }
  return "NoSuchDay"
type Fahrenheit float
func (t Fahrenheit) String() string
{ return fmt.Sprintf("%.1f°F", t) }
Note that these methods
do not take a pointer (although they could).
This is not the same notion as
Java's Integer type:
it's really an int (float).
There is no box.
type Stringer interface { String() string }
func print(args ...Stringer)
{ for i, s := range args
    { if i > 0
       { os.Stdout.WriteString(" ") }
print(Day(1), Fahrenheit(72.29))
=> Monday 72.3°F
Again, these methods do not take a pointer,
although another type might define
a String() method that does,
and it too would satisfy Stringer.
Empty Interface:
The empty interface (interface {})
has no methods.
Every type satisfies the empty interface.
func print(args ...interface{})
{ for i, arg := range args
   { if i > 0 { os.Stdout.WriteString(" ") }
      switch a := arg.(type)
     { // "type switch"
     case Stringer: os.Stdout.WriteString(a.String())
     case int: os.Stdout.WriteString(itoa(a))
     case string: os.Stdout.WriteString(a)
     // more types can be used
     default: os.Stdout.WriteString("????")
print(Day(1), "was", Fahrenheit(72.29))
=> Monday was 72.3°F

Small and implicit
Fahrenheit and Day satisfied Stringer implicitly;
other types might too.
A type satisfies an interface simply by
implementing its methods.
There is no "implements" declaration;
interfaces are satisfied implicitly.
It's a form of duck typing,
but (usually) checkable at compile time.
An object can (and usually does)
satisfy many interfaces simultaneously.
For instance, Fahrenheit and Day satisfy Stringer
and also the empty interface.
In Go, interfaces are usually small:
one or two or even zero methods.
type Reader interface
{ Read(p []byte) (n int, err os.Error) }
// And similarly for Writer
Anything with a Read method implements Reader.
- Sources: files, buffers, network connections, pipes
- Filters: buffers, checksums, decompressors, decrypters
JPEG decoder takes a Reader, so it can decode from disk,
network, gzipped HTTP, ....
Buffering just wraps a Reader:
var bufferedInput Reader =
Fprintf uses a Writer:
func Fprintf(w Writer, fmt string, a ...interface{})

Interfaces can be retrofitted:
Had an existing RPC implementation
that used custom wire format.
Changed to an interface:
type Encoding interface
 { ReadRequestHeader(*Request) os.Error
   ReadRequestBody(interface{}) os.Error
   WriteResponse(*Response, interface{}) os.Error
   Close() os.Error
Two functions (send, recv) changed signature.
func sendResponse
  (sending *sync.Mutex, req *Request
  , reply interface{}
  , enc *gob.Encoder
  , errmsg string) 
After (and similarly for receiving):
func sendResponse
  (sending *sync.Mutex
  , req *Request
  , reply interface{}
  , enc Encoding
  , errmsg string)
That is almost the whole change
to the RPC implementation.

Post facto abstraction:
We saw an opportunity:
RPC needed only Encode and Decode methods.
Put those in an interface
and you've abstracted the codec.
Total time: 20 minutes,
including writing and testing the
JSON implementation of the interface.
(We also wrote a trivial wrapper
to adapt the existing codec
for the new rpc.Encoding interface.)
In Java,
RPC would be refactored
into a half-abstract class,
subclassed to create
JsonRPC and StandardRPC.
In Go,
there is no need to manage a type hierarchy:
just pass in an encoding interface stub
(and nothing else).
Systems software must often manage
connections and clients.
Go provides independently executing goroutines
that communicate and synchronize
using channels.
Analogy with Unix:
processes connected by pipes.
But in Go things are fully typed
and lighter weight.
Start a new flow of control with the go keyword.
Parallel computation is easy:
func main() {
  go expensiveComputation(x, y, z)
  anotherExpensiveComputation(a, b, c)
Roughly speaking, a goroutine is like
a thread, but lighter weight:
- stacks are small, segmented, sized on demand
- goroutines are muxed [multiplexed] by demand
onto true threads
- requires support from
language, compiler, runtime
- can't just be a C++ library
Thread per connection:
Doesn't scale in practice,
so in most languages
we use event-driven callbacks
and continuations.
But in Go,
a goroutine per connection model scales well.
for {
  rw := socket.Accept()
  conn := newConn(rw, handler)
  go conn.serve()
Our trivial parallel program again:
func main() {
  go expensiveComputation(x, y, z)
  anotherExpensiveComputation(a, b, c)
Need to know when the computations are done.
Need to know the result.
A Go channel provides the capability:
a typed synchronous communications mechanism.
Goroutines communicate using channels.
func computeAndSend(x, y, z int) chan int
{ ch := make(chan int)
  go func()
    {ch <- expensiveComputation(x, y, z)}()
  return ch
func main()
{ ch := computeAndSend(x, y, z)
  v2 := anotherExpensiveComputation(a, b, c)
  v1 := <-ch
  fmt.Println(v1, v2)

A worker pool:
Traditional approach (C++, etc.) is to
communicate by sharing memory:
- shared data structures protected by mutexes
Server would use shared memory
to apportion work:
type Work struct
 { x, y, z int assigned
 , done bool
type WorkSet struct
{ mu sync.Mutex
  work []*Work
But not in Go.
Share memory by communicating
In Go, you reverse the equation.
- channels use the
operator to
synchronize and communicate
Typically don't need or want mutexes.
type Work struct { x, y, z int }
func worker(in <-chan *Work, out chan <- *Work)
{ for w := range in
  { w.z = w.x * w.y
    out <- w
func main()
{ in, out := make(chan *Work), make(chan *Work)
  for i := 0; i < 10; i++
     { go worker(in, out) }
  go sendLotsOfWork(in)

Garbage collection:
Automatic memory management
simplifies life.
GC is critical for concurrent programming;
otherwise it's too fussy
and error-prone to track ownership
as data moves around.
GC also clarifies design.
A large part of the design
of C and C++ libraries
is about deciding who owns memory,
who destroys resources.
But garbage collection isn't enough.
Memory safety:
Memory in Go is intrinsically safer:
pointers but no pointer arithmetic
no dangling pointers
(locals move to heap as needed)
no pointer-to-integer conversions
   ( Package unsafe allows this
   but labels the code as dangerous;
   used mainly in some low-level libraries.)
all variables are zero-initialized
all indexing is bounds-checked
Should have far fewer buffer overflow exploits.
Systems language:
By systems language, we mean
suitable for writing systems software.
- web servers
- web browsers
- web crawlers
- search indexers
- databases
- compilers
- programming tools (debuggers, analyzers, ...)
- IDEs
- operating systems (maybe)
Systems programming:
loadcode.blogspot.com 2009:
"[Git] is known to be very fast.
It is written in C.
A Java version JGit was made.
It was considerably slower.
Handling of memory and lack of unsigned types
[were] some of the important reasons."
Shawn O. Pearce (git mailing list):
"JGit struggles with not having
an efficient way to represent a SHA-1.
C can just say "unsigned char[20]"
and have it inline into the
container's memory allocation.
A byte[20] in Java will cost
an *additional* 16 bytes of memory,
and be slower to access
because the bytes themselves
are in a different area of memory
from the container object."
Control of bits and memory:
Like C, Go has
- full set of unsigned types
- bit-level operations
- programmer control of memory layout
type T struct
 { x int
   buf [20]byte [...]
- pointers to inner values
p := &t.buf

Simplicity and clarity:
Go's design aims for being easy to use,
which means it must be easy to understand,
even if that sometimes contradicts
superficial ease of use.
Some examples:
No implicit numeric conversions,
although the way constants work
ameliorates the inconvenience.

No method overloading.
For a given type,
there is only one method
with that name.
There is no "public" or "private" label.
Instead, items with UpperCaseNames
are visible to clients;
lowerCaseNames are not.
Numeric constants are "ideal numbers":
no size or signed/unsigned distinction,
hence no L or U or UL endings.
077 // octal
1 << 100
Syntax of literal determines default type:
1.234e5 // float
1e2 // float
100 // int
But they are just numbers
that can be used at will
and assigned to variables
with no conversions necessary.
seconds := time.Nanoseconds()/1e9
// result has integer type

High precision constants:
Arithmetic with constants is high precision.
Only when assigned to a variable
are they rounded or truncated to fit.
const MaxUint = 1<<32 - 1
const Ln2
= 0.6931471805599453094172321214581\
const Log2E = 1/Ln2 // accurate reciprocal
var x float64 = Log2E // rounded to nearest float64 value
The value assigned to x
will be as precise as possible
in a 64-bit float.

And more:
There are other aspects of Go
that make it easy and expressive
yet scalable and efficient:
- clear package structure
- initialization
- clear rules about how a program
begins execution
- top-level initializing
functions and values
- composite values
var freq =
map[string]float{"C4":261.626, "A4":440}
// etc.
- tagged values
var s = Point{x:27, y:-13.2}
- function literals and closures
go func() { for { c1 <- <-c2 } }()
- reflection
- and more....
Plus automatic document generation and formatting.
Go is different:

Go is object-oriented not type-oriented:
– inheritance is not primary
– methods on any type,
but no classes or subclasses
Go is (mostly) implicit not explicit:
– types are inferred not declared
– objects have interfaces
but they are derived, not specified
Go is concurrent not parallel:
– intended for program structure,
not max performance
– but still can keep all the cores busy
– ... and many programs are
more nicely expressed with concurrent ideas
even if not parallel at all .
The language is designed and usable.
Two compiler suites:
Gc, written in C,
generates OK code very quickly.
- unusual design based on the
Plan 9 compiler suite
Gccgo, written in C++,
generates good code more slowly
- uses GCC's code generator and tools
Libraries good and growing,
but some pieces are still preliminary.
Garbage collector works fine
(simple mark and sweep)
but is being rewritten for more concurrency,
less latency.
Available for Linux etc., Mac OS X.
Windows port underway.
All available as open source.

Go was the 2009 TIOBE "Language of the year"
two months after it was released.
"I have reimplemented a networking project
from Scala to Go.
Scala code is 6000 lines.
Go is about 3000.
Even though Go does not have the power of abbreviation,
the flexible type system
seems to out-run Scala
when the programs start getting longer.
Hence, Go produces much shorter code asymptotically."
- Petar Maymounkov
"Go is unique because of the
set of things it does well.
It has areas for improvement,
but for my needs it is the best match
when compared to: C, C++, C#, D, Java,
Erlang, Python, Ruby, and Scala."
- Hans Stimer

For those on the team,
it's the main day-to-day language now.
It has rough spots but mostly in the libraries,
which are improving fast.
Productivity seems much higher.
(I get behind on mail much more often.)
Most builds take a fraction of a second.
Starting to be used inside Google
for some production work.
We haven't built truly large software in Go yet,
but all indicators are positive.
Try it out:
This is a true open source project
-- Full source, documentation and much more
... you're welcome to fork it too!
(issue#9 considers renaming the project):
Comment 120 by cjaramilu, Nov 11, 2009
"Gol", it is soccer goal in spanish
Comment 134 by stefan.midjich, Nov 11, 2009
Comment 242 by sekour, Nov 11, 2009
Comment 711 by phio.asia, Nov 12, 2009
"Qu", which means "Go" in Chinese :-) .]
Rob Pike, Another Go at Language Design
Wednesday, April 28, 2010