go tutorial

8/8/2019 Go Tutorial

1/16

Introduction----

This document is a tutorial introduction to the basics of the Go programminglanguage, intended for programmers familiar with C or C++. It is not a comprehensive

guide to the language; at the moment the document closest to that is thelanguage specification.After you've read this tutorial, you might want to look atEffective Go,which digs deeper into how the language is used.Also, slides from a 3-day course about Go are available:Day 1,Day 2,Day 3.

The presentation here proceeds through a series of modest programs to illustratekey features of the language. All the programs work (at time of writing) and ar

echecked into the repository in the directory "/doc/progs/".

Program snippets are annotated with the line number in the original file; forcleanliness, blank lines remain blank.

Hello, World----

Let's start in the usual way:

--PROG progs/helloworld.go /package/ END

Every Go source file declares, using a "package" statement, which package it's part of.It may also import other packages to use their facilities.This program imports the package "fmt" to gain access toour old, now capitalized and package-qualified, friend, "fmt.Printf".

Functions are introduced with the "func" keyword.The "main" package's "main" function is where the program starts running (afterany initialization).

String constants can contain Unicode characters, encoded in UTF-8.

(In fact, Go source files are defined to be encoded in UTF-8.)

The comment convention is the same as in C++:

/* ... */// ...

Later we'll have much more to say about printing.

Semicolons----

You might have noticed that our program has no semicolons. In Go

code, the only place you typically see semicolons is separating theclauses of "for" loops and the like; they are not necessary afterevery statement.


2/16

In fact, what happens is that the formal language uses semicolons,much as in C or Java, but they are inserted automaticallyat the end of every line that looks like the end of a statement. Youdon't need to type them yourself.

For details about how this is done you can see the language

specification, but in practice all you need to know is that younever need to put a semicolon at the end of a line. (You can putthem in if you want to write multiple statements per line.) As anextra help, you can also leave out a semicolon immediately beforea closing brace.

This approach makes for clean-looking, semicolon-free code. Theone surprise is that it's important to put the openingbrace of a construct such as an "if" statement on the same line asthe "if"; if you don't, there are situations that may not compileor may give the wrong result. The language forces the brace styleto some extent.

Compiling----

Go is a compiled language. At the moment there are two compilers."Gccgo" is a Go compiler that uses the GCC back end. There is also asuite of compilers with different (and odd) names for each architecture:"6g" for the 64-bit x86, "8g" for the 32-bit x86, and more. Thesecompilers run significantly faster but generate less efficient codethan "gccgo". At the time of writing (late 2009), they also havea more robust run-time system although "gccgo" is catching up.

Here's how to compile and run our program. With "6g", say,

$ 6g helloworld.go # compile; object goes into helloworld.6$ 6l helloworld.6 # link; output goes into 6.out$ 6.outHello, world; or ; o

$

Wit

"gccgo" it oo

itt

mo

t

dition .

$ gccgo

owo

d.go$ .outH

o, wo

d; o

; o

$

Ec

o----

N

xt up,

' v

ion of t

Unix uti ity "

c

o(1)":

--PROG p

og /

c

o.go /p c

g

/ END

T

i p

og

m i m but it' doing numb

of n

w t

ing . In t

t

x mp

,w

w "func" int

oduc

function. T

ywo

d "v

", "con t", nd "typ

"(not u

d y

t) o int

oduc

d

c

tion , do

"impo

t".

Notic

t

t w

c n g

oup d

c

tion of t

m

o

t intop

nt

iz

d i t , on

it

m p

in

, on in

7-10 nd 14-17.But it' not n

c

y to do o; w

cou d

v

id


3/16

con t Sp c

= " "con t N

w in

= "\n"

T

i p

og

m impo

t t

""o "" p c

g

to cc

it "Stdout" v

i b

, of typ

"*o .Fi

". T

"impo

t" t t

m

nt i ctu y d

c

tion: in it g

n

fo

m, u

d in ou

``

o wo

d'' p

og

m,it n m

t

id

ntifi ("fmt")t

t wi b

u

d to cc

m

mb

of t

p c

g

impo

t

d f

om t

fi

(""fmt""),found in t

cu nt di cto

y o

in t nd

d oc tion.In t

i p

og

m, t

oug

, w

'v

d

opp

d t

xp icit n m

f

om t

impo

t ; by d

f u t,p c

g

impo

t

d u ing t

n m

d

fin

d by t

impo

t

d p c

g

,w

ic

by conv

ntion i of cou

t

fi

n m

it

f. Ou

``

o wo

d'' p

og

mcou d

v

id ju t "impo

t "fmt"".

You c n p

cify you

own impo

t n m

if you w nt but it' on y n

c

y if you n d to o v

n ming conf ict.

Giv

n "o .Stdout" w

c n u

it "W

it

St

ing" m

t

od to p

int t

t

ing.

H ving impo

t

d t

"f g" p c

g

, in

12 c t

g ob v

i b

to

o dt

v u

of

c

o' "-n" f g. T

v

i b

"omitN

w in

"

typ

"*boo ", point

to "boo ".

In "m in.m in", w

p

t

gum

nt ( in

20) nd t

n c t

oc t

ing v

i b

w

wi u

to bui d t

output.

T

d

c

tion t t

m

nt

t

fo

m

v

t

ing = ""

T

i i t

"v

"

ywo

d, fo ow

d by t

n m

of t

v

i b

, fo ow

d byit typ

, fo ow

d by n

qu ign nd n initi v u

fo

t

v

i b

.

Go t

i

to b

t

, nd t

i d

c

tion cou d b

o

t

n

d. Sinc

t

t

ing con t nt i of typ

t

ing, w

don't

v

to t

t

compi

t

t.W

cou d w

it

v

= ""

o

w

cou d go

v

n

o

t

nd w

it

t

idiom

:= ""

T

":=" op

to

i u

d ot in Go to

p

nt n initi izing d

c

tion.T

' on

in t

"fo

" c u

on t

n

xt in

:

--PROG p

og /

c

o.go /fo

/

T

"f g" p c

g

p

d t

gum

nt nd

ft t

non-f g

gum

nt

in i t t

t c n b

it

t

d ov

in t

obviou w y.

T

Go "fo

" t t

m

nt diff

f

om t

t of C in numb

of w y . Fi

t,


4/16

it' t

on y ooping con t

uct; t

i no "w

i

" o

"do". S

cond,t

no p nt

on t

c u

, but t

b

c

on t

body

m nd to

y. T

m

pp i

to t

"if" nd " witc

" t t

m

nt .L t

x mp

wi

ow om

ot

w y "fo

" c n b

w

itt

n.

T

body of t

oop bui d up t

t

ing " " by pp

nding (u ing "+=")t

gum

nt nd

p

ting p c

. Aft

t

oop, if t

"-n" f g i not

t, t

p

og

m pp

nd n

w in

. Fin y, it w

it

t

u t.

Notic

t

t "m in.m in" i ni dic function wit

no tu

n typ

.It' d

fin

d t

t w y. F ing off t

nd of "m in.m in" m

n '' ucc

''; if you w nt to ign n on

ou tu

n, c

o .Exit(1)

T

"o " p c

g

cont in ot

nti fo

g

tting t

t

d; fo

in t nc

, "o .A

g " i ic

u

d by t

"f g" p c

g

to cc

t

comm nd- in

gum

nt .

An Int

ud

bout Typ

----

Go

om

f mi i

typ

uc

"int" nd "f o t", w

ic

p

ntv u

of t

'' pp

op

i t

'' iz

fo

t

m c

in

. It o d

fin

xp icit y- iz

d typ

uc

"int8", "f o t64", nd o on, p u un ign

d int

g typ

uc

"uint", "uint32",

tc. T

di tinct typ

;

v

n if "int" nd "int32" bot

32 bit in iz

,t

y not t

m

typ

. T

i o "byt

" ynonym fo

"uint8", w

ic

i t

m

nt typ

fo

t

ing .

Sp

ing of " t

ing", t

t' bui t-in typ

w

. St

ing

immut b

v u

&md

;t

y not ju t y of "byt

" v u

.

Onc

you'v

bui t t

ing v u

, you c n't c

ng

it, t

oug

of cou

you c n c

ng

t

ing v

i b

imp y by

igning it. T

i nipp

t f

om " t

ing .go" i

g cod

:

--PROG p

og / t

ing .go /

o/ /ci o/

How

v

t

fo owing t t

m

nt

i

g b

c u

t

y wou d modify " t

ing" v u

:

[0] = 'x'(*p)[1] = 'y'

In C++ t

m

, Go

t

ing

bit

i

"con

t

t

ing

", w

i

point

to t

ing

n ogou to "con t t

ing"

f

nc

.

Y

, t

point

. How

v

, Go imp ifi

t

i

u

itt

;

d on.

A

y

d

c

d i

t

i :

v

yOfInt [10]int

A

y , i

t

ing ,

v u

, but t

y

mut b

. T

i diff

f

om C, in w

ic

"

yOfInt" wou d b

u b

point

to "int".In Go, inc

y

v u

, it' m

ningfu ( nd u

fu ) to t

bout point

to

y .

T

iz

of t

y i p

t of it typ

;

ow

v

, on

c n d

c


5/16

ic

v

i b

to

o d f nc

to ny y, of ny iz

,wit

t

m

m

nt typ

.A ic

xp

ion

t

fo

m " [ ow :

ig

]",

p

ntingt

int n y ind

x

d f

om " ow" t

oug

"

ig

-1"; t

u ting ic

i ind

x

d f

om "0" t

oug

"

ig

- ow-1".In

o

t, ic

oo

ot i

y but wit

no

xp icit iz

("[]" v . "[10]") nd t

y

f

nc

gm

nt of n und ying, u u y nonymou , gu

y. Mu tip

ic

c n

d t if t

y p

nt pi

c

of t

m

y;mu tip

y c n n

v

d t .

S ic

muc

mo common in Go p

og

m t

n gu

y ; t

y' mo f

xib

,

v

f nc

m ntic , nd

ffici

nt. W

t t

y c

i t

p

ci

cont

o of to

g

yout of gu

y; if you w nt to

v

und d

m

nt of n y to d wit

in you

t

uctu , you

ou d u

gu

y. To c t

on

, u

compound v u

con t

ucto

&md

; n

xp

ion fo

m

d

f

om

typ

fo

ow

d by

b

c

-bound

d

xp

ion

i

t

i

:

[3]int{1,2,3}

In t

i c

t

con t

ucto

bui d n y of 3 "int ".

W

n p

ing n y to function, you mo t

w y w nt

to d

c t

fo

m p

m

t to b

ic

. W

n you c t

function, ic

t

y to c t

(

ffici

nt y) ic

f nc

nd p

t

t.By d

f u t, t

ow nd upp bound of ic

m tc

t

nd of t

xi ting obj

ct, o t

conci

not tion "[:]"wi ic

t

w

o

y.

U ing ic

on

c n w

it

t

i function (f

om " um.go"):

--PROG p

og / um.go / um/ /^}/

Not

ow t

tu

n typ

("int") i d

fin

d fo

" um()" by t ting it ft

t

p

m

t

i t.

To c t

function, w

ic

t

y. T

i int

ic t

c (w

'

ow imp

w y in mom

nt) con t

uct n

y nd ic

it:

:=

um([3]int{1,2,3}[:])

If you

c

ting

gu

y but w nt t

compi

to count t

m

nt fo

you, u

"..." t

y iz

:

:= um([...]int{1,2,3}[:])

T

t' fu i

t

n n

c

y, t

oug

.In p

ctic

, un

you'

m

ticu ou bout to

g

yout wit

in d t t

uctu

, ic

it

f&md

;u ing

mpty b

c

t wit

no iz

&md

;i you n

d:

:= um([]int{1,2,3})

T

o m p , w

ic

you c n initi iz

i

t

i :


6/16

m := m p[ t

ing]int{"on

":1 , "two":2}

T

bui t-in function "

n()", w

ic

tu

n numb

of

m

nt ,m

it fi

t pp

nc

in " um". It wo

on t

ing ,

y , ic

, m p , nd c

nn

.

By t

w y, not

t

ing t

t wo

on t

ing ,

y , ic

, m p nd c

nn

i t

"

ng

" c u

on "fo

" oop . In t

d of w

iting

fo

i := 0; i & t;

n( ); i++ { ... }

to oop ov t

m

nt of ic

(o

m p o

...) , w

cou d w

it

fo

i, v :=

ng

{ ... }

T

i ign "i" to t

ind

x nd "v" to t

v u

of t

ucc

iv

m

nt of t

t

g

t of t

ng

. S

<

f='/doc/

ff

ctiv

_go.

tm '>Eff

ctiv

Gofo

mo

x mp

of it u

.

An Int ud

bout A oc tion

----

Mo t typ

in Go v u

. If you

v

n "int" o

" t

uct"o

n y,

ignm

ntcopi

t

cont

nt of t

obj

ct.To oc t

n

w v

i b

, u

"n

w()", w

ic

tu

n point to t

oc t

d to

g

.

typ

T t

uct { , b int }v

t *T = n

w(T)

o

t

mo

idiom tic

t := n

w(T)

Som

typ

&md

;m p , ic

, nd c

nn

(

b

ow)&md

;

v

f

nc

m ntic .If you'

o ding ic

o

m p nd you modify it cont

nt , ot

v

i b

f

ncing t

m

und

ying d t wi

t

modific tion. Fo

t

t

typ

you w nt to u

t

bui t-in function "m

()":

m := m

(m p[ t

ing]int)

T

i t t

m

nt initi iz

n

w m p

dy to to

nt

i

.If you ju t d

c

t

m p, in

v

m m p[ t

ing]int

it c

t

"ni "

f

nc

t

t c nnot

o d nyt

ing. To u

t

m p,you mu t fi

t initi iz

t

f

nc

u ing "m

()" o

by ignm

nt f

om n

xi ting m p.

Not

t

t "n

w(T)"

tu

n typ

"*T" w

i

"m

(T)"

tu

n typ

"T". If you (mi t

n y) oc t

f

nc

obj

ct wit

"n

w()",you

c

iv

point

to ni

f

nc

,

quiv

nt to

d

c

ing n uniniti iz

d v

i b

nd t

ing it dd

.

An Int

ud

bout Con t nt


7/16

----

A t

oug

int

g

com

in ot of iz

in Go, int

g

con t nt do not.T

no con t nt i

"0LL" o

"0x0UL". In t

d, int

g

con t nt

v u t

d

g

-p ci ion v u

t

tc n ov f ow on y w

n t

y

ign

d to n int

g v

i b

wit

too itt

p

ci ion to

p

nt t

v u

.

con t

dEig

t = (1 & t;& t; 100) >> 97 //

g

T

nu nc

t

t d

v

di

ction to t

g

of t

ngu g

p

cific tion but

om

i u t

tiv

x mp

:

v

uint64 = 0 //

typ

uint64, v u

0 := uint64(0) //

quiv

nt; u

"conv

ion"i := 0x1234 // i g

t d

f u t typ

: intv

j int = 1

6 //

g - 1000000 i p

nt b

in n intx := 1.5 // f o ti3div2 := 3/2 // int

g

divi ion -

u t i 1

f3div2 := 3./2. // f

o

ting point divi

ion -

u

t i

1.5

Conv ion on y wo

fo

imp

c

uc

conv ting "int " of on

ign o

iz

to not

, nd b

tw

n "int " nd "f o t ", p u f

w ot

imp

c

. T

no utom tic num ic conv ion of ny

ind in Go,ot

t

n t

t of m

ing con t nt

v

conc t

iz

nd typ

w

n

ign

d to v

i b

.

An I/O P c

g

----

N

xt w

' oo

t imp

p c

g

fo

doing fi

I/O wit

t

u u o

t of op

n/c o

/ d/w

it

int f c

. H ' t

t

t of "fi

.go":

--PROG p

og /fi

.go /p c

g

/ /^}/

T

fi

t f

w in

d

c

t

n m

of t

p c

g

&md

;"fi

"&md

; nd t

n impo

t two p c

g

. T

"o "p c

g

id

t

diff

nc

b

tw

n v

iou op

ting y t

m to giv

con i t

nt vi

w of fi

nd o on;

w

'

going to u

it

o

nd ing uti iti

nd

p

oduc

t

udim

nt of it fi

I/O.

T

ot

it

m i t

ow-

v

,

xt

n " y c " p c

g

, w

ic

p

ovid

p

imitiv

int

f c

to t

und

ying op

ting y t

m' c .

N

xt i typ

d

finition: t

"typ

"

ywo

d int

oduc

typ

d

c

tion,in t

i c

d t t

uctu

c

d "Fi

".To m

t

ing itt

mo

int

ting, ou

"Fi

" inc ud

t

n m

of t

fi

t

t t

fi

d

c

ipto

f

to.

B

c u

"Fi

" t

t wit

c pit

tt

, t

typ

i v i b

out id

t

p c

g

,t

t i , by u

of t

p c

g

. In Go t

u

bout vi ibi ity of info

m tion i

imp

: if n m

(of top-

v

typ

, function, m

t

od, con t nt o

v

i b

,o

of t

uctu

fi

d o

m

t

od) i c pit iz

d, u

of t

p c

g

m y

it. Ot

wi

, t

n m

nd

nc

t

t

ing b

ing n m

d i vi ib

on y in id

t

p c

g

in w

ic


8/16

it i d

c d. T

i i mo t

n conv

ntion; t

u

i

nfo

c

d by t

compi .In Go, t

t

m fo

pub ic y vi ib

n m

i ''

xpo

t

d''.

In t

c

of "Fi

", it fi

d ow c

nd o invi ib

to u ,but w

wi oon giv

it om

xpo

t

d, upp

-c

m

t

od .

Fi

t, t

oug

,

i f cto

y to c t

"Fi

":

--PROG p

og /fi

.go /n

wFi

/ /^}/

T

i tu

n point to n

w "Fi

" t

uctu wit

t

fi

d

c

ipto

nd n m

fi

d in. T

i cod

u

Go' notion of ''compo it

it

'', n ogou tot

on

u

d to bui d m p nd y , to con t

uct n

w

p- oc t

dobj

ct. W

cou d w

it

n := n

w(Fi

)

n.fd = fdn.n m

= n m

tu

n n

but fo

imp

t

uctu i

"Fi

" it'

i to tu

n t

dd of compo it

it ,

i don

on in

21.

W

c n u

t

f cto

y to con t

uct om

f mi i

,

xpo

t

d v

i b

of typ

"*Fi

":

--PROG p

og /fi

.go /v

/ /^.$/

T

"n

wFi

" function w not

xpo

t

d b

c u

it' int n . T

p

op ,

xpo

t

d f cto

y to u

i "Op

n":

--PROG p

og /fi

.go /func.Op

n/ /^}/

T

numb

of n

w t

ing in t

f

w in

. Fi

t, "Op

n"

tu

n mu tip

v u

, "Fi

" nd n

o

(mo

bout

o

in mom

nt).W

d

c

t

mu ti-v u

tu

n p

nt

iz

d i t of d

c

tion ; ynt ctic yt

y oo

ju t i

cond p

m

t

i t. T

function" y c .Op

n" o

mu ti-v u

tu

n, w

ic

w

c n g

b wit

t

mu ti-v

i b

d

c

tion on in

31; it d

c

"

" nd "

" to

o d t

two v u

,

bot

of typ

"int" (

t

oug

you'd

v

to

oo

t t

"

y

c

" p

c

g

to

t

t). Fin y, in

35

tu

n two v u

: point

to t

n

w "Fi

" nd t

o

. If " y c .Op

n" f i , t

fi

d

c

ipto

"

" wi b

n

g tiv

nd "n

wFi

" wi

tu

n "ni ".

About t

o

o

: T

"o " ib

y inc ud

g

n

notion of n

o

.It' good id

to u

it f ci ity in you

own int

f c

, w

do

, fo

con i t

nt

o

nd ing t

oug

out Go cod

. In "Op

n" w

u

conv

ion to t

n t

Unix' int

g

"

no" v u

into t

int

g

typ

"o .E

no", w

ic

imp

m

nt "o .E

o

".

Now t

t w

c n bui d "Fi

", w

c n w

it

m

t

od fo

t

m. To d

c

m

t

od of typ

, w

d

fin

function to

v

n

xp icit

c

iv

of t

t typ

, p c

din p

nt

b

fo

t

function n m

. H

om

m

t

od fo

"*Fi

",

c

of w

ic

d

c

c

iv

v

i b

"fi

".


9/16

--PROG p

og /fi

.go /C o

/ END

T

i no imp icit "t

i " nd t

c

iv

v

i b

mu t b

u

d to cc

m

mb of t

t

uctu . M

t

od not d

c d wit

int

" t

uct" d

c

tion it

f. T

" t

uct" d

c

tion d

fin

on y d t m

mb

.

In f ct, m

t

od c n b

c

t

d fo

mo t ny typ

you n m

, uc

n int

g

o

y, not ju t fo

" t

uct ". W

' n

x mp

wit

y t .

T

"St

ing" m

t

od i o c

d b

c u

of p

inting conv

ntion w

' d

c

ib

t .

T

m

t

od u

t

pub ic v

i b

"o .EINVAL" to

tu

n t

("o .E

o

"v ion of t

) Unix o

cod

"EINVAL". T

"o " ib

y d

fin

t nd

d

t of uc

o

v u

.

W

c n now u

ou

n

w p c

g

:

--PROG p

og /

owo

d3.go /p c

g

/ END

T

''"./"'' in t

impo

t of ''"./fi

"'' t

t

compi

to u

ou

own p c

g

t

t

n om

t

ing f

om t

di cto

y of in t

d p c

g

.(A

o, ''"fi

.go"'' mu t b

compi

d b

fo w

c n impo

t t

p c

g

.)

Now w

c n compi

nd

un t

p

og

m:

$ 6g fi

.go # compi

fi

p c

g

$ 6g

owo

d3.go # compi

m in p c

g

$ 6 -o

owo

d3

owo

d3.6 # in

- no n

d to m

ntion "fi

"$

owo

d3

o, wo

dc n't op

n fi

;

=No uc

fi

o

di

cto

y$

Rotting c t ----

Bui ding on t

"fi

" p c

g

,

' imp

v

ion of t

Unix uti ity "c t(1)","p

og /c t.go":

--PROG p

og /c t.go /p c

g

/ END

By now t

i

ou d b

y to fo ow, but t

" witc

" t t

m

nt int

oduc

om

n

w f

tu

. Li

"fo

" oop, n "if" o

" witc

" c n inc ud

niniti iz tion t t

m

nt. T

" witc

" on in

18 u

on

to c

t

v

i b

"n

" nd "

" to

o d t

tu

n v u

f

om "f.R

d()". (T

"if" on in

25

t

m

id

.) T

" witc

" t t

m

nt i g

n

: it

v u t

t

c

f

om top to bottom oo

ing fo

t

fi

t c

t

t m tc

t

v u

; t

c

xp

ion don't n

d to b

con t nt o

v

n int

g

, ong t

y

v

t

m

typ

.

Sinc

t

" witc

" v u

i ju t "t

u

", w

cou d

v

it off&md

; i o

t

itu tionin "fo

" t t

m

nt, mi ing v u

m

n "t

u

". In f ct, uc

" witc

"i fo

m of "if-

" c

in. W

i

w

'

, it

ou d b

m

ntion

d t

t in


10/16

" witc

" t t

m

nt

c

"c

"

n imp icit "b

".

Lin

25 c "W

it

()" by icing t

incoming buff

, w

ic

i it

f ic

.S ic

p

ovid

t

t nd

d Go w y to

nd

I/O buff

.

Now

t' m

v

i nt of "c t" t

t option

y do

"

ot13" on it input.It'

y to do by ju t p

oc

ing t

byt

, but in t

d w

wi

xp oit

Go' notion of n int

f c

.

T

"c t()" ub

outin

u

on y two m

t

od of "f": "R

d()" nd "St

ing()", o

t' t

t by d

fining n int

f c

t

t

x ct y t

o

two m

t

od .H i cod

f

om "p

og /c t_

ot13.go":

--PROG p

og /c t_

ot13.go /typ

. d / /^}/

Any typ

t

t

t

two m

t

od of " d "&md

; g

d

of w

t

v

ot

m

t

od t

typ

m y o

v

&md

;i id to imp

m

nt t

int f c

. Sinc

"fi

.Fi

" imp

m

nt t

m

t

od , it imp

m

nt t

"

d

" int

f c

. W

cou d tw

t

"c t" ub

outin

to cc

pt "

d

"

in

t

d of

"*fi

.Fi

"

nd it wou

d wo

ju

t fin

, but

t'

mb

i

itt

fi

t by w

iting

cond typ

t

t imp

m

nt " d ", on

t

t w

p n

xi ting "

d

" nd do

"

ot13" on t

d t . To do t

i , w

ju t d

fin

t

typ

nd imp

m

nt t

m

t

od nd wit

no ot

boo

ping,w

v

cond imp

m

nt tion of t

" d " int f c

.

--PROG p

og /c t_

ot13.go /typ

.

ot t

13/ /

nd.of.

ot t

13/

(T

"

ot13" function c

d on in

42 i t

ivi nd not wo

t

p

oducing

.)

To u

t

n

w f

tu , w

d

fin

f g:

--PROG p

og /c t_

ot13.go /

ot13F g/

nd u

it f

om wit

in mo t y unc

ng

d "c t()" function:

--PROG p

og /c t_

ot13.go /func.c t/ /^}/

(W

cou d o do t

w

pping in "m in" nd

v

"c t()" mo t y on

,

xc

ptfo

c

nging t

typ

of t

gum

nt; con id

t

t n

x

ci

.)Lin

56 t

oug

58

t it up: If t

"

ot13" f g i t

u

, w

p t

"

d

"w

c

iv

d into "

ot t

13" nd p

oc

d. Not

t

t t

int

f c

v

i b

v

u

, not point

: t

gum

nt i

of typ

"

d

", not "*

d

", v

n t

oug

und

t

cov

it

o d point

to " t

uct".

H

it i in ction:

$

c

o bcd

fg

ij

mnopq

tuvwxyz ./c t bcd

fg

ij

mnopq

tuvwxyz$

c

o bcd

fg

ij

mnopq

tuvwxyz ./c t --

ot13nopq

tuvwxyz bcd

fg

ij

m$
/pp>
F n of d

p

nd

ncy inj

ction m y t

c

f

om

ow

i y int

f c

ow u to ub titut

t

imp

m

nt tion of fi

d

c

ipto

.


11/16

Int f c

di tinctiv

f

tu of Go. An int f c

i imp

m

nt

d by typ

if t

typ

imp

m

nt t

m

t

od d

c d in t

int f c

.T

i m

n t

t typ

m y imp

m

nt n

bit

y numb

of diff

nt int

f c

.T

i no typ

i

c

y; t

ing c n b

muc

mo d

oc,

w

w wit

"

ot13". T

typ

"fi

.Fi

" imp

m

nt " d "; it cou d

oimp

m

nt "w

it

", o

ny ot

int

f c

bui t f

om it m

t

od t

t

fit t

cu

nt itu tion. Con id

t

mpty int

f c

typ

Empty int

f c

{}

Ev y typ

imp

m

nt t

mpty int f c

, w

ic

m

itu

fu fo

t

ing i

cont in

.

So

ting----

Int

f

c

p

ovid

imp

fo

m of po

ymo

p

i

m. T

y comp

t

y

p

t

t

d

finition of w

t n obj

ct do

f

om

ow it do

it,

owingdi tinct imp

m

nt tion to b

p

nt

d t diff nt tim

by t

m

int

f c

v

i b

.

A n

x mp

, con id t

i imp

o

t go

it

m t

n f

om "p

og / o

t.go":

--PROG p

og / o

t.go /func.So

t/ /^}/

T

cod

n d on y t

m

t

od , w

ic

w

w

p into o

t' "Int f c

":

--PROG p

og / o

t.go /int f c

/ /^}/

W

c n pp y "So

t" to ny typ

t

t imp

m

nt "L

n", "L

", nd "Sw p".T

" o

t" p c

g

inc ud

t

n

c

y m

t

od to ow o

ting of

y of int

g

, t

ing ,

tc.;

' t

cod

fo

y of "int"

--PROG p

og / o

t.go /typ

.*IntA

y/ /Sw p/

H

w

m

t

od d

fin

d fo

non-" t

uct" typ

. You c n d

fin

m

t

od fo

ny typ

you d

fin

nd n m

in you

p c

g

.

And now

outin

to t

t it out, f

om "p

og / o

tm in.go". T

i u

function in t

" o

t" p c

g

, omitt

d

fo

b

vity,to t

t t

t t

u t i o

t

d.

--PROG p

og / o

tm in.go /func.int / /^}/

If w

v

n

w typ

w

w nt to b

b

to o

t, w

n

d to do i to imp

m

nt t

t

m

t

od fo

t

t typ

, i

t

i :

--PROG p

og / o

tm in.go /typ

.d y/ /Sw p/

P

inting----

T

x mp

of fo

m tt

d p

inting o f

v

b

n mod

t. In t

i

ction

w

' t

bout

ow fo

m tt

d I/O c n b

don

w

in Go.

W

'v

n imp

u

of t

p c

g

"fmt", w

ic


12/16

imp

m

nt "P

intf", "Fp

intf", nd o on.Wit

in t

"fmt" p c

g

, "P

intf" i d

c d wit

t

i ign tu :

P

intf(fo

m t t

ing, v ...int

f c

{}) (n int,

no o .E

o

)

T

to

n "..." int

oduc

v

i b

-

ngt

gum

nt i t t

t in C wou db

nd

d u ing t

" td

g.

" m c

o .

In Go, v

i dic function

p

d ic

of t

gum

nt of t

p

cifi

d typ

. In "P

intf"' c

, t

d

c

tion y "...int f c

{}" o t

ctu

typ

i ic

of

mpty int f c

v u

, "[]int f c

{}"."P

intf" c n

x min

t

gum

nt by it

ting ov

t

ic

nd, fo

c

m

nt, u ing typ

witc

o

t

f

ction ib

yto int p t t

v u

.It' off topic

but uc

un-tim

typ

n y i

p

xp in om

of t

nic

p

op

ti

of Go' "P

intf",du

to t

bi ity of "P

intf" to di cov t

typ

of it

gum

nt dyn mic y.

Fo

x mp

, in C

c

fo

m t mu t co

pond to t

typ

of it

gum

nt. It'

i

in m

ny c

in Go. In

t

d of "%

ud" youc n ju t y "%d"; "P

intf"

now t

iz

nd ign

dn

of t

int

g nd c n do t

ig

t t

ing fo

you. T

nipp

t

--PROG p

og /p

int.go 'NR==10' 'NR==11'

p

int

18446744073709551615 -1

In f ct, if you' zy t

fo

m t "%v" wi

p

int, in imp

pp

op

i t

ty

, ny v u

,

v

n n y o

t

uctu . T

output of

--PROG p

og /p

int.go 'NR==14' 'NR==20'

i

18446744073709551615 {77 Sun

t St

ip} [1 2 3 4]

You c n d

op t

fo

m tting tog

t

if you u

"P

int" o

"P

int n"in t

d of "P

intf". T

o

outin

do fu y utom tic fo

m tting.T

"P

int" function ju t p

int it

m

nt out u ing t

quiv

ntof "%v" w

i

"P

int n" in

t p c

b

tw

n

gum

nt nd dd n

w in

. T

output of

c

of t

two in

i id

ntic to t

t of t

"P

intf" c bov

.

--PROG p

og /p

int.go 'NR==21' 'NR==22'

If you

v

you

own typ

you'd i

"P

intf" o

"P

int" to fo

m t,ju t giv

it "St

ing()" m

t

od t

t

tu

n t

ing. T

p

int

outin

wi

x min

t

v u

to inqui

w

t

it imp

m

nt t

m

t

od nd if o, u

it

t

t

n om

ot

fo

m tting.H

' imp

x mp

.

--PROG p

og /p

int_ t

ing.go 'NR==9' END

Sinc

"*t

tTyp

"

"St

ing()" m

t

od, t

d

f u t fo

m tt

fo

t

t typ

wi u

it nd p

oduc

t

output

77 Sun

t St

ip


13/16

Ob v

t

t t

"St

ing()" m

t

od c "Sp

int" (t

obviou Gov

i nt t

t tu

n t

ing) to do it fo

m tting; p

ci fo

m tt c n u

t

"fmt" ib

y

cu

iv

y.

Anot

f

tu of "P

intf" i t

t t

fo

m t "%T" wi p

int t

ing p

nt tion of t

typ

of v u

, w

ic

c n b

ndy w

n d

buggingpo ymo

p

ic cod

.

It' po ib

to w

it

fu cu tom p

int fo

m t wit

f g nd p ci ion nd uc

, but t

t' g

tting itt

off t

m in t

d o w

'

v

it n

xp o

tion

x

ci

.

You mig

t

, t

oug

,

ow "P

intf" c n t

w

t

typ

imp

m

nt t

"St

ing()" m

t

od. Actu

y w

t it do

i

if t

v u

c nb

conv

t

d to n int

f c

v

i b

t

t imp

m

nt t

m

t

od.Sc

m tic y, giv

n v u

"v", it do

t

i :

typ

St

ing

int

f c

{

St

ing()

t

ing}

, o

:= v.(St

ing

) // T

t w

t

v imp

m

nt "St

ing()"if o

{

u t = .St

ing()}

{

u t = d

f u tOutput(v)}

T

cod

u

``typ

tion'' ("v.(St

ing )") to t

t if t

v u

to din"v" ti fi

t

"St

ing " int f c

; if it do

, " "

wi b

com

n int

f c

v

i b

imp

m

nting t

m

t

od nd "o

" wi b

"t

u

". W

t

n u

t

int

f c

v

i b

to c t

m

t

od.(T

''comm , o

'' p tt

n i Go idiom u

d to t

t t

ucc

ofop

tion uc

typ

conv

ion, m p upd t

, communic tion , nd o on, t

oug

t

i i t

on y pp

nc

in t

i tuto

i .)If t

v u

do

not ti fy t

int

f c

, "o

" wi b

f

.

In t

i nipp

t t

n m

"St

ing

" fo ow t

conv

ntion t

t w

dd ''[

]

''to int

f c

d

c

ibing imp

m

t

od

t i

t

i .

On

t w

in

. To comp

t

t

uit

, b

id

"P

intf"

tc. nd "Sp

intf"

tc., t

o "Fp

intf"

tc. Un i

in C, "Fp

intf"' fi

t

gum

nt i

not

fi

. In

t

d, it i

v

i

b

of typ

"io.W

it

", w

ic

i

nint

f c

typ

d

fin

d in t

"io" ib

y:

typ

W

it

int

f c

{W

it

(p []byt

) (n int,

o .E

o

)}

(T

i int

f c

i not

conv

ntion n m

, t

i tim

fo

"W

it

"; t

o"io.R

d

", "io.R

dW

it

", nd o on.)T

u you c n c "Fp

intf" on ny typ

t

t imp

m

nt t nd

d "W

it

()"m

t

od, not ju t fi

but o n

two

c

nn

, buff

, w

t

v

you w nt.

P

im

numb

----


14/16

Now w

com

to p

oc

nd communic tion&md

;concu nt p

og

mming.It' big ubj

ct o to b

b

i

f w

um

om

f mi i

ity wit

t

topic.

A c ic p

og

m in t

ty

i p

im

i

v

.(T

i

v

of E

to t

n

i comput tion

y mo

ffici

nt t

nt

go

it

m p

nt

d

, but w

mo

int

t

d in concu

ncy t

n go

it

mic t t

mom

nt.)It wo

by t

ing t m of t

n tu

numb nd int

oducing

qu

nc

of fi t , on

fo

c

p

im

, to winnow t

mu tip

oft

t p

im

. At

c

t

p w

v

qu

nc

of fi t

of t

p

im

o f

, nd t

n

xt numb to pop out i t

n

xt p

im

, w

ic

t

igg t

c tion of t

n

xt fi t in t

c

in.

H

' f ow di g

m;

c

box

p

nt fi t

m

nt w

o

c tion i t

igg d by t

fi

t numb t

t f ow

d f

om t

m

nt b

fo it.

&nb p;&nb p;&nb p;&nb p;&nb p;

To c t

t m of int

g , w

u

Go c

nn

, w

ic

,bo owing f

om CSP' d

c

nd nt , p

nt communic tion c

nn

t

t c n conn

ct two concu nt comput tion .In Go, c

nn

v

i b

f nc

to

un-tim

obj

ct t

tcoo

din t

t

communic tion;

wit

m p nd ic

, u

"m

" to c t

n

w c

nn

.

H i t

fi

t function in "p

og / i

v

.go":

--PROG p

og / i

v

.go /S

nd/ /^}/

T

"g

n

t

" function

nd t

qu

nc

2, 3, 4, 5, ... to it

gum

nt c

nn

, "c

", u ing t

bin

y communic tion op

to

"& t;-".C

nn

op

tion b oc

, o if t

' no

cipi

nt fo

t

v u

on "c

",t

nd op

tion wi w it unti on

b

com

v i b

.

T

"fi t

" function

t

gum

nt : n input c

nn

, n outputc

nn

, nd p

im

numb

. It copi

v u

f

om t

input to t

output, di c

ding nyt

ing divi ib

by t

p

im

. T

un

y communic tion op

to

"& t;-" (

c

iv

)

t

i

v

t

n

xt v u

on t

c

nn

.

--PROG p

og / i

v

.go /Copy.t

/ /^}/

T

g

n

to

nd fi t

x

cut

concu

nt y. Go

it own mod

of p

oc

/t

d / ig

t-w

ig

t p

oc

/co

outin

, o to void not tion confu ion w

c concu

nt y

x

cutingcomput tion in Go go

outin

. To t

t go

outin

,invo

t

function, p

fixing t

c wit

t

ywo

d "go";t

i t

t t

function

unning in p

wit

t

cu

ntcomput tion but in t

m

dd

p c

:

go um(

ug

A

y) // c cu t

um in t

b c

g

ound

If you w nt to

now w

n t

c cu tion i don

, p c

nn

on w

ic

it c n

po

t b c

:


15/16

c

:= m

(c

n int)go um(

ug

A y, c

)// ... do om

t

ing

fo

w

i

u t := & t;-c

// w it fo

, nd

t

i

v

,

u t

B c

to ou

p

im

i

v

. H '

ow t

i

v

pip

in

i titc

dtog

t

:

--PROG p

og / i

v

.go /func.m in/ /^}/

Lin

29 c

t

t

initi c

nn

to p to "g

n

t

", w

ic

itt

n t

t up. A

c

p

im

pop out of t

c

nn

, n

w "fi t "i dd

d to t

pip

in

nd it output b

com

t

n

w v u

of "c

".

T

i

v

p

og

m c n b

tw

d to u

p tt n commonin t

i ty

of p

og

mming. H i v

i nt v ionof "g

n t

", f

om "p

og / i

v

1.go":

--PROG p

og

/

i

v

1.go /func.g

n

t

/ /^}/

T

i v ion do

t

tup int n

y. It c t

t

outputc

nn

, unc

go

outin

unning function it

, nd tu

n t

c

nn

to t

c . It i f cto

y fo

concu nt

x

cution, t

ting t

go

outin

nd tu

ning it conn

ction.

T

function it not tion ( in

12-16) ow u to con t

uct n nonymou function nd invo

it on t

pot. Notic

t

t t

oc v

i b

"c

" i v i b

to t

function it nd iv

on

v

n ft "g

n t

" tu

n .

T

m

c

ng

c n b

m d

to "fi t ":

--PROG p

og / i

v

1.go /func.fi t

/ /^}/

T

" i

v

" function' m in oop b

com

imp

nd c

u t, nd w

i

w

'

t it

t' tu

n it into f cto

y too:

--PROG p

og / i

v

1.go /func. i

v

/ /^}/

Now "m in"' int

f c

to t

p

im

i

v

i c

nn

of p

im

:

--PROG p

og / i

v

1.go /func.m in/ /^}/

Mu

tip

xing----

Wit

c

nn

, it' po ib

to

v

mu tip

ind

p

nd

nt c i

nt go

outin

wit

outw

iting n

xp icit mu tip

x

. T

t

ic

i to

nd t

v

c

nn

in t

m

g

,w

ic

it wi t

n u

to

p y to t

o

igin

nd

.A

i tic c i

nt-

v

p

og

m i ot of cod

, o

i v

y imp

ub titut

to i u t

t

t

id

. It t

t by d

fining "

qu

t" typ

, w

ic

mb

d c

nn

t

t wi b

u

d fo

t

p y.

--PROG p

og /

v

.go /typ

.

qu

t/ /^}/


16/16

T

v wi b

t

ivi : it wi do imp

bin

y op tion on int

g . H

' t

cod

t

t invo

t

op

tion nd

pond to t

qu

t:

--PROG p

og / v .go /typ

.binOp/ /^}/

Lin

14 d

fin

t

n m

"binOp" to b

function t

ing two int

g

nd

tu

ning t

i

d.

T

" v "

outin

oop fo v , c

iving qu

t nd, to void b oc

ing du

to ong-

unning op tion, t

ting go

outin

to do t

ctu wo

.

--PROG p

og / v .go /func. v / /^}/

W

con t

uct v in f mi i

w y, t

ting it nd tu

ning c

nn

conn

ct

d to it:

--PROG p

og /

v

.go /func. t

tS

v

/ /^}/

H ' imp

t

t. It t

t v wit

n ddition op to

nd

nd out"N"

qu

t wit

out w iting fo

t

p i

. On y ft

t

qu

t

ntdo

it c

c

t

u t .

--PROG p

og / v .go /func.m in/ /^}/

On

nnoy nc

wit

t

i p

og

m i t

t it do

n't

ut down t

v c

n y;w

n "m in" tu

n t

numb of ing ing go

outin

b oc

d on communic tion. To o v

t

i ,

w

c n p

ovid

cond, "quit" c

nn

to t

v

:

--PROG p

og /

v

1.go /func. t

tS

v

/ /^}/

It p

t

quit c

nn

to t

"

v

" function, w

ic

u

it i

t

i :

--PROG p

og /

v

1.go /func.

v

/ /^}/

In id

"

v

", t

"

ct" t t

m

nt c

oo

w

ic

of t

mu tip

communic tion

i t

d by it c

c n p

oc

d. If

b oc

d, it w it unti on

c n p

oc

d; if

mu

tip

c

n p

oc

d, it c

oo

on

t

ndom. In t

i

in

t

nc

, t

"

ct" ow t

v

to

ono

qu

t unti it

c

iv

quit m

g

, t w

ic

point it

tu

n , t

min ting it

x

cution.

A t

t'

ft i to t

ob

t

"quit" c

nn

t t

nd of m in:

--PROG p

og /

v

1.go / dd

,.quit/...--PROG p

og /

v

1.go /quit....t

u

/

T

' ot mo

to Go p

og

mming nd concu

nt p

og

mming in g

n

but t

i quic

tou

ou d giv

you om

of t

b ic .

go tutorial

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