The Go Programming Language Design FAQ
Origins
Why are you creating a new language?
TODO
What is the history of the project?
TODO
What are Go's ancestors?
Go is mostly in the C family (basic syntax), with significant input from the Pascal/Modula/Oberon family (declarations, packages), plus it borrows some ideas from languages inspired by Tony Hoare's CSP, such as Newsqueak and Limbo (concurrency). However, it is a new language across the board. In every respect the language was designed by thinking about what programmers do and how to make programming, at least the kind of programming we do, more effective, which means more fun.
Who are the protagonists?
Robert Griesemer, Rob Pike and Ken Thompson laid out the goals and
original specification of the language. Ian Taylor read the draft
specification and decided to write gccgo. Russ
Cox joined later and helped move the language and libraries from
prototype to reality.
Changes from C
Why is the syntax so different from C?
Other than declaration syntax, the differences are not major and stem from two desires. First, the syntax should feel light, without too many mandatory keywords, repetition, or arcana. Second, the language has been designed to be easy to parse. The grammar is conflict-free and can be parsed without a symbol table. This makes it much easier to build tools such as debuggers, dependency analyzers, automated documentation extractors, IDE plug-ins, and so on. C and its descendants are notoriously difficult in this regard but it's not hard to fix things up.
Why are declarations backwards?
They're only backwards if you're used to C. In C, the notion is that a
variable is declared like an expression denoting its type, which is a
nice idea, but the type and expression grammars don't mix very well and
the results can be confusing; consider function pointers. Go mostly
separates expression and type syntax and that simplifies things (using
prefix * for pointers is an exception that proves the rule). In C,
the declaration
int* a, b;
declares a to be a pointer but not b; in Go
var a, b *int;
declares both to be pointers. This is clearer and more regular.
Also, the := short declaration form argues that a full variable
declaration should present the same order as := so
var a uint64 = 1;has the same effect as
a := uint64(1);
Parsing is also simplified by having a distinct grammar for types that
is not just the expression grammar; keywords such as func
and chan keep things clear.
Why is there no pointer arithmetic?
Safety. Without pointer arithmetic it's possible to create a language that can never derive an illegal address that succeeds incorrectly. Compiler and hardware technology have advanced to the point where a loop using array indices can be as efficient as a loop using pointer arithmetic. Also, the lack of pointer arithmetic can simplify the implementation of the garbage collector.
Why are ++ and -- statements and not expressions? And why postfix, not prefix?
Without pointer arithmetic, the convenience value of pre- and postfix
increment operators drops. By removing them from the expression
hierarchy altogether, expression syntax is simplified and the messy
issues around order of evaluation of ++ and --
(consider f(i++) and p[i] = q[i++])
are eliminated as well. The simplification is
significant. As for postfix vs. prefix, either would work fine but
the postfix version is more traditional; insistence on prefix arose
with the STL, part of a language whose name contains, ironically, a
postfix increment.
Absent features
Why does Go not have generic types?
Generics may well come at some point. We don't feel an urgency for them, although we understand some programmers do.
Generics are convenient but they come at a cost in complexity in the type system and run-time. We haven't yet found a design that gives value proportionate to the complexity, although we continue to think about it. Meanwhile, Go's built-in maps and slices, plus the ability to use the empty interface to construct containers (with explicit unboxing) mean in many cases it is possible to write code that does what generics would enable, if less smoothly.
This remains an open issue.
Why does Go not have exceptions?
Exceptions are a similar story. A number of designs for exceptions have been proposed but each adds significant complexity to the language and run-time. By their very nature, they span functions and perhaps even goroutines; they have wide-ranging implications. There is also concern about the effect exceptions would have on the libraries. They are, by definition, exceptional yet experience with other languages that support them show they have profound effect on library and interface definition. It would be nice to find a design that allows them to be truly exceptional without encouraging common errors to turn into special control flow requiring every programmer to compensate.
Like generics, exceptions remain an open issue.
Why does Go not have assertions?
This is answered in the general FAQ.
TODO
TODO:
Why does Go not have: - macros? - conditional compilation? What do you have planned? - variant types? explain: package design slices oo separate from storage (abstraction vs. implementation) why garbage collection? no data in interfaces concurrency questions: goroutine design why aren't maps atomic why csp inheritance? embedding? dependency declarations in the language oo questions dynamic dispatch clean separation of interface and implementation why no automatic numeric conversions? make vs new Why do maps only work on builtin types?