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The Origins of Go

Like biolog ical species, successf ul langu ages beget offspring that incor porate the advantages of

their ancestors; int erbre e ding som etimes leads to sur prising strengt hs; and, ver y occasionally,

a radic al ne w fe ature arises wit hout pre cedent. We can lear n a lot about why a langu age is the

way it is and what env iro nment it has been adapt ed for by looking at these influences.

The figure below shows the most imp ortant influences of earlier programming langu ages on

the desig n of Go.

Go is som etimes des crib ed as a ‘‘C-li ke langu age,’’ or as ‘‘C for the 21st century.’’ Fr om C, Go

in her ite d its expression syntax, cont rol-flow statements, basic dat a types, cal l-by-value param￾eter passing, point ers, and above all, C’s emp hasis on programs that compi le to efficient

machine code and cooperate natural ly wit h the abstrac tions of cur rent operat ing systems.

The Go Programming Language

© 2016 Alan A. A. Donovan & Brian W. Kernighan

revision 3b600c, date 29 Sep 2015

ptg16091132

THE ORIGINS OF GO xiii

But there are other ancestors in Go’s fami ly tre e. One maj or stream of influence comes fro m

languages by Nik laus Wir th, beg inning wit h Pascal. Modula-2 inspired the package con cept.

Ob ero n eliminated the distinc tion bet ween module int erface files and module imp lementation

files. Obero n-2 influence d the syntax for packages, imports, and declarat ions, and Obj e ct

Ob ero n prov ide d the syntax for met hod declarat ions.

Anot her lineage among Go’s ancestors, and one that makes Go distinc tive among recent

prog ramming langu ages, isa sequence of lit tle-k now n research langu ages deve lop ed at Bel l

Labs, all ins pired by the con cept of commu nicating sequent ial pro cesses (CSP) fro m To ny

Ho are’s seminal 1978 pap er on the found ation s of con cur rency. In CSP,aprogram isaparal lel

comp osition of processes that have no share d st ate; the pro cesses communic ate and synchro￾nize using channel s. But Hoare’s CSP was a for mal langu age for des cribing the fundament al

concepts of con cur rency, not a programming langu age for writing exe cut able programs.

Rob Pike and others began to exp eriment wit h CSP imp lementation s as actu al langu ages. The

firs t was cal le d Sque ak (‘‘A langu age for communic ating wit h mice’’), which provide d a lan￾gu age for handling mou se and key board events, wit h st atically cre ate d ch annel s. This was

fo llowe d by Newsque ak, which offered C-li ke statement and expression syntax and Pas cal-li ke

type not ation. It was a purely functional langu age wit h garb age col lec tion, again aimed at

managing key board , mous e, and window events. Channel s became firs t-class values, dynami￾cally cre ate d and storable in variables.

The Plan9operat ing system car r ied these ide as forward in a langu age cal le d Alef. Alef tried

to make Newsque ak a viable system programming langu age, but its omission of garb age col￾le ction made conc urrency too painf ul.

Ot her cons tructions in Go show the influence of non-ancestral genes here and there; for

example iota is loosely fro m APL, and lexic al scop e with neste d func tions is fro m Scheme

(and most langu ages since). Here too we find nove l mu tat ions. Go’s innovat ive slices provide

dy namic arrays wit h efficient random access but als o permit sop histicate d sh aring

ar rangements reminiscent of lin ked lists. And the defer st atement is new wit h Go.

The Go Project

Al l prog ramming langu ages reflec t the programming phi losop hy of their creators, which often

includes a significant component of reaction to the perceive d shortcomings of earlier lan￾gu ages. The Go pro jec t was bor ne of frust rat ion wit h several sof tware systems at Google that

were suf fer ing fro m an explosion of complexity. (This pro blem is by no means unique to

Go ogle.)

As Rob Pike put it, ‘‘comp lexity is multiplic ative’’: fixingapro blem by mak ing one par t of the

system more complex slowly but surely adds complexity to other par ts. Wi th con stant pres￾sure to add features and opt ion s and configurat ions, and to ship code quickly, it’s easy to

neglec t simplicity, even thoug h in the lon g run simplicity is the key to good sof tware.

The Go Programming Language

© 2016 Alan A. A. Donovan & Brian W. Kernighan

revision 3b600c, date 29 Sep 2015

ptg16091132

xiv PREFACE

Simp licity requires more wor k at the beg inning ofapro jec t to reduce an idea to its essence and

more dis cip line over the lifet ime of a pro jec t to distinguish good changes fro m bad or per nicious ones. Wit h sufficient effor t,agood change can be accommodated wit hout compromising what Fre d Brooks cal le d the ‘‘conceptu al int egr ity’’ of the desig n butabad change cannot,

andaper nicious change trades simplicity for its shallow cou sin, conv enience. Only through

simplicity of desig n canasystem remain stable, sec ure , and coh erent as it grows.

The Go pro jec t includes the langu age its elf, its tools and stand ard librar ies, and last but not

le ast, a cultural agenda of radic al simplicity. Asarecent hig h-leve l language , Go has the bene-

fit of hindsig ht, and the basics are don e we ll: it has garbage col lec tion,apackage system, firs tcl ass functions, lexic al scop e,asystem cal l interface, and immut able str ings in which text is

general ly encoded in UTF-8. But it has comp arat ive ly few features and is unlikely to add

more . Fo r inst ance, it has no imp licit numer ic conv ersions, no con str uctor s or destr uctor s, no

op erator overloading, no defau lt parameter values, no inher itance, no gener ics, no exception s,

no macros, no function annot ation s, and no thread-lo cal storage. The langu age is mature and

st able, and guarante es backwards compatibi lit y: older Go programs can be compi led and run

with newer versions of compi lers and stand ard librar ies.

Go has enough ofatyp e system to avoid most of the careless mistakes that plague programmers in dynamic langu ages, but it has a simpler typ e system than comparable typ ed langu ages.

This appro ach can som etimes lead to isolate d pockets of ‘‘untyped’’ prog ramming wit hin a

broader framewor k of typ es, and Go programmers do not go to the lengt hs that C++ or

Haskel l prog rammers do to express safet y prop erties as typ e-bas ed pro ofs. But in prac tice Go

gives programmers much of the safet y and run-t ime per for mance benefits ofarel ative ly

st ron g type system wit hout the burden ofacomplex one.

Go encourages an awareness of contemp orar y comp uter system desig n, partic ularly the

importance of locality. Its bui lt-in dat a types and most librar y data str uctures are craf ted to

work natural ly wit hout explicit initializat ion or imp licit con str uctor s, so rel ative ly few memor y al location s and memor y wr ites are hidden in the code. Go’s aggregate typ es (str ucts and

ar rays) hold their elements direc tly, requir ing less storage and fewer allo cat ions and point er

indirec tion s than langu ages that use indirec t fields. And since the moder n comp uter isaparal lel machine, Go has conc urrency features bas ed on CSP, as mention ed earlier. The var iablesize stacks of Go’s lig htweig ht threads or goro utines are initial ly small enoug h that creating one

goro utine is che ap and cre ating a million is prac tic al.

Go’s stand ard librar y, often descr ibed as coming wit h ‘‘batt eries include d,’’ prov ides cle an

building blo cks and APIs for I/O, text pro cessing, graphics, cryptography, net wor king, and

dist ribut ed app lic ations, wit h supp ort for many stand ard file for mats and pro tocol s. The

librar ies and tools make extensive use of convent ion to reduce the need for configurat ion and

explanation, thu s simplif ying program logic and mak ing diverse Go programs more simi lar to

each other and thu s easier to learn. Pro jec ts bui lt using the go to ol use only file and identifier

names and an occ asional speci al comment to deter mine all the librar ies, exec utables, tests,

benchmarks, examples, platfor m-specific var iants, and documentation for a proj e ct; the Go

source its elf cont ains the bui ld sp ecification.