mirror of
https://github.com/golang/go
synced 2024-11-21 18:04:40 -07:00
- Add introduction section (1 page), essentially a condensed form
of an earlier intro. - Updated contents section. - Removed left-over text from earlier documents. No spec changes. R=r DELTA=379 (147 added, 227 deleted, 5 changed) OCL=21312 CL=21331
This commit is contained in:
Robert Griesemer
parent
67a7abad7f
commit
6715358652
384
doc/go_spec.txt
384
doc/go_spec.txt
@ -3,9 +3,9 @@ The Go Programming Language Specification (DRAFT)
|
||||
|
||||
Robert Griesemer, Rob Pike, Ken Thompson
|
||||
|
||||
----
|
||||
(December 16, 2008)
|
||||
|
||||
----
|
||||
|
||||
This document is a semi-formal specification of the Go systems
|
||||
programming language.
|
||||
@ -15,6 +15,7 @@ This document is not ready for external review, it is under active development.
|
||||
Any part may change substantially as design progresses.
|
||||
</font>
|
||||
|
||||
----
|
||||
|
||||
<!--
|
||||
Timeline (9/5/08):
|
||||
@ -128,6 +129,13 @@ Contents
|
||||
----
|
||||
|
||||
Introduction
|
||||
Guiding principles
|
||||
Program structure
|
||||
Modularity, identifiers and scopes
|
||||
Typing, polymorphism, and object-orientation
|
||||
Pointers and garbage collection
|
||||
Values and references
|
||||
Multithreading and channels
|
||||
|
||||
Notation
|
||||
|
||||
@ -207,11 +215,11 @@ Contents
|
||||
Goto statements
|
||||
|
||||
Function declarations
|
||||
Method declarations
|
||||
Predeclared functions
|
||||
Length and capacity
|
||||
Conversions
|
||||
Allocation
|
||||
Method declarations
|
||||
Predeclared functions
|
||||
Length and capacity
|
||||
Conversions
|
||||
Allocation
|
||||
|
||||
Packages
|
||||
|
||||
@ -223,6 +231,129 @@ Contents
|
||||
Introduction
|
||||
----
|
||||
|
||||
Go is a new systems programming language intended as an alternative to C++ at
|
||||
Google. Its main purpose is to provide a productive and efficient programming
|
||||
environment for compiled programs such as servers and distributed systems.
|
||||
|
||||
|
||||
Guiding principles
|
||||
----
|
||||
|
||||
The design of Go is motivated by the following goals (in no particular order):
|
||||
|
||||
- very fast compilation, instantaneous incremental compilation
|
||||
- strongly typed
|
||||
- procedural
|
||||
- concise syntax avoiding repetition
|
||||
- few, orthogonal, and general concepts
|
||||
- support for threading and interprocess communication
|
||||
- garbage collection
|
||||
- container library written in Go
|
||||
- efficient code, comparable to other compiled languages
|
||||
|
||||
|
||||
Program structure
|
||||
----
|
||||
|
||||
A Go program consists of a number of ``packages''.
|
||||
|
||||
A package is built from one or more source files, each of which consists
|
||||
of a package specifier followed by declarations. There are no statements at
|
||||
the top level of a file.
|
||||
|
||||
By convention, the package called "main" is the starting point for execution.
|
||||
It contains a function, also called "main", that is the first function invoked
|
||||
by the run time system after initialization (if a source file within the program
|
||||
contains a function "init()", that function will be executed before "main.main()"
|
||||
is called).
|
||||
|
||||
Source files can be compiled separately (without the source code of packages
|
||||
they depend on), but not independently (the compiler does check dependencies
|
||||
by consulting the symbol information in compiled packages).
|
||||
|
||||
|
||||
Modularity, identifiers and scopes
|
||||
----
|
||||
|
||||
A package is a collection of import, constant, type, variable, and function
|
||||
declarations. Each declaration binds an ``identifier'' with a program entity
|
||||
(such as a variable).
|
||||
|
||||
In particular, all identifiers in a package are either declared explicitly
|
||||
within the package, arise from an import statement, or belong to a small set
|
||||
of predeclared identifiers (such as "string").
|
||||
|
||||
Scoping follows the usual rules: The scope of an identifier declared within
|
||||
a ``block'' generally extends from the declaration of the identifier to the
|
||||
end of the block. An identifier shadows identifiers with the same name declared
|
||||
in outer scopes. Within a scope, an identifier can be declared at most once.
|
||||
|
||||
A package may mark explicitly declared identifiers for ``export'' to make them
|
||||
visible to other source files in the same package, or to other packages.
|
||||
|
||||
|
||||
Typing, polymorphism, and object-orientation
|
||||
----
|
||||
|
||||
Go programs are strongly typed. Certain variables may be polymorphic.
|
||||
The language provides mechanisms to make use of such polymorphic variables
|
||||
type-safe.
|
||||
|
||||
Object-oriented programming is supported by interface types.
|
||||
Different interface types are independent of each
|
||||
other and no explicit hierarchy is required (such as single or
|
||||
multiple inheritance explicitly specified through respective type
|
||||
declarations). Interface types only define a set of methods that a
|
||||
corresponding implementation must provide. Thus interface and
|
||||
implementation are strictly separated.
|
||||
|
||||
An interface is implemented by associating methods with types. If a type
|
||||
defines all methods of an interface, it implements that interface and thus
|
||||
can be used where that interface is required. Unless used through a variable
|
||||
of interface type, methods can always be statically bound (they are not
|
||||
``virtual''), and invoking them incurs no extra run-time overhead compared
|
||||
to ordinary functions.
|
||||
|
||||
Go has no explicit notion of classes, sub-classes, or inheritance.
|
||||
These concepts are trivially modeled in Go through the use of
|
||||
functions, structures, embedding of types, associated methods, and interfaces.
|
||||
|
||||
Go has no explicit notion of type parameters or templates. Instead,
|
||||
containers (such as stacks, lists, etc.) are implemented through the
|
||||
use of abstract operations on interface types.
|
||||
|
||||
|
||||
Pointers and garbage collection
|
||||
----
|
||||
|
||||
Variables may be allocated automatically (when entering the scope of
|
||||
the variable) or explicitly on the heap. Pointers are used to refer
|
||||
to heap-allocated variables. Pointers may also be used to point to
|
||||
any other variable; such a pointer is obtained by "taking the
|
||||
address" of that variable. Variables are automatically reclaimed when
|
||||
they are no longer accessible. There is no pointer arithmetic in Go.
|
||||
|
||||
|
||||
Values and references
|
||||
----
|
||||
|
||||
All objects have value semantics, but their contents may be accessed
|
||||
through different pointers referring to the same object.
|
||||
For example, when calling a function with an array, the array is
|
||||
passed by value, possibly by making a copy. To pass a reference,
|
||||
one must explicitly pass a pointer to the array.
|
||||
|
||||
|
||||
Multithreading and channels
|
||||
----
|
||||
|
||||
Go supports multithreaded programming directly. A function may
|
||||
be invoked as a parallel thread of execution. Communication and
|
||||
synchronization are provided through channels and their associated
|
||||
language support.
|
||||
|
||||
|
||||
----
|
||||
|
||||
Notation
|
||||
----
|
||||
@ -274,6 +405,7 @@ A production may be referenced from various places in this document
|
||||
but is usually defined close to its first use. Productions and code
|
||||
examples are indented.
|
||||
|
||||
----
|
||||
|
||||
Source code representation
|
||||
----
|
||||
@ -315,6 +447,7 @@ Letters and digits
|
||||
|
||||
All non-ASCII code points are considered letters; digits are always ASCII.
|
||||
|
||||
----
|
||||
|
||||
Vocabulary
|
||||
----
|
||||
@ -538,6 +671,8 @@ The following words are reserved and must not be used as identifiers:
|
||||
continue for import return var
|
||||
|
||||
|
||||
----
|
||||
|
||||
Declarations and scope rules
|
||||
----
|
||||
|
||||
@ -921,6 +1056,7 @@ export directive.
|
||||
export sin, cos
|
||||
export math.abs
|
||||
|
||||
----
|
||||
|
||||
Types
|
||||
----
|
||||
@ -1583,6 +1719,8 @@ As an example, "T0" and "T1" are equal but not identical because they have
|
||||
different declarations.
|
||||
|
||||
|
||||
----
|
||||
|
||||
Expressions
|
||||
----
|
||||
|
||||
@ -2362,6 +2500,8 @@ TODO: Complete this list as needed.
|
||||
Constant expressions can be evaluated at compile time.
|
||||
|
||||
|
||||
----
|
||||
|
||||
Statements
|
||||
----
|
||||
|
||||
@ -2884,6 +3024,8 @@ clause of the switch statement.
|
||||
FallthroughStat = "fallthrough" .
|
||||
|
||||
|
||||
----
|
||||
|
||||
Function declarations
|
||||
----
|
||||
|
||||
@ -3069,6 +3211,8 @@ into a faster internal call that doesn't do slicing).
|
||||
-->
|
||||
|
||||
|
||||
----
|
||||
|
||||
Packages
|
||||
----
|
||||
|
||||
@ -3168,6 +3312,8 @@ Here is a complete example Go package that implements a concurrent prime sieve:
|
||||
}
|
||||
|
||||
|
||||
----
|
||||
|
||||
Program initialization and execution
|
||||
----
|
||||
|
||||
@ -3233,229 +3379,3 @@ When main.main() returns, the program exits.
|
||||
|
||||
TODO: is there a way to override the default for package main or the
|
||||
default for the function name main.main?
|
||||
|
||||
|
||||
<!--
|
||||
----
|
||||
----
|
||||
UNUSED PARTS OF OLD DOCUMENT go_lang.txt - KEEP AROUND UNTIL NOT NEEDED ANYMORE
|
||||
----
|
||||
|
||||
Guiding principles
|
||||
----
|
||||
|
||||
Go is a new systems programming language intended as an alternative to C++ at
|
||||
Google. Its main purpose is to provide a productive and efficient programming
|
||||
environment for compiled programs such as servers and distributed systems.
|
||||
|
||||
The design is motivated by the following guidelines:
|
||||
|
||||
- very fast compilation (1MLOC/s stretch goal); instantaneous incremental compilation
|
||||
- procedural
|
||||
- strongly typed
|
||||
- concise syntax avoiding repetition
|
||||
- few, orthogonal, and general concepts
|
||||
- support for threading and interprocess communication
|
||||
- garbage collection
|
||||
- container library written in Go
|
||||
- reasonably efficient (C ballpark)
|
||||
|
||||
The language should be strong enough that the compiler and run time can be
|
||||
written in itself.
|
||||
|
||||
|
||||
Program structure
|
||||
----
|
||||
|
||||
A Go program consists of a number of ``packages''.
|
||||
|
||||
A package is built from one or more source files, each of which consists
|
||||
of a package specifier followed by import declarations followed by other
|
||||
declarations. There are no statements at the top level of a file.
|
||||
|
||||
By convention, one package, by default called main, is the starting point for
|
||||
execution. It contains a function, also called main, that is the first function
|
||||
invoked by the run time system.
|
||||
|
||||
If a source file within the program
|
||||
contains a function init(), that function will be executed
|
||||
before main.main() is called.
|
||||
|
||||
Source files can be compiled separately (without the source
|
||||
code of packages they depend on), but not independently (the compiler does
|
||||
check dependencies by consulting the symbol information in compiled packages).
|
||||
|
||||
|
||||
Modularity, identifiers and scopes
|
||||
----
|
||||
|
||||
A package is a collection of import, constant, type, variable, and function
|
||||
declarations. Each declaration associates an ``identifier'' with a program
|
||||
entity (such as a type).
|
||||
|
||||
In particular, all identifiers in a package are either
|
||||
declared explicitly within the package, arise from an import statement,
|
||||
or belong to a small set of predefined identifiers (such as "int32").
|
||||
|
||||
A package may make explicitly declared identifiers visible to other
|
||||
packages by marking them as exported; there is no ``header file''.
|
||||
Imported identifiers cannot be re-exported.
|
||||
|
||||
Scoping is essentially the same as in C: The scope of an identifier declared
|
||||
within a ``block'' extends from the declaration of the identifier (that is, the
|
||||
position immediately after the identifier) to the end of the block. An identifier
|
||||
shadows identifiers with the same name declared in outer scopes. Within a
|
||||
block, a particular identifier must be declared at most once.
|
||||
|
||||
|
||||
Typing, polymorphism, and object-orientation
|
||||
----
|
||||
|
||||
Go programs are strongly typed. Certain values can also be
|
||||
polymorphic. The language provides mechanisms to make use of such
|
||||
polymorphic values type-safe.
|
||||
|
||||
Interface types provide the mechanisms to support object-oriented
|
||||
programming. Different interface types are independent of each
|
||||
other and no explicit hierarchy is required (such as single or
|
||||
multiple inheritance explicitly specified through respective type
|
||||
declarations). Interface types only define a set of methods that a
|
||||
corresponding implementation must provide. Thus interface and
|
||||
implementation are strictly separated.
|
||||
|
||||
An interface is implemented by associating methods with types.
|
||||
If a type defines all methods of an interface, it
|
||||
implements that interface and thus can be used where that interface is
|
||||
required. Unless used through a variable of interface type, methods
|
||||
can always be statically bound (they are not ``virtual''), and incur no
|
||||
run-time overhead compared to an ordinary function.
|
||||
|
||||
[OLD
|
||||
Interface types, building on structures with methods, provide
|
||||
the mechanisms to support object-oriented programming.
|
||||
Different interface types are independent of each
|
||||
other and no explicit hierarchy is required (such as single or
|
||||
multiple inheritance explicitly specified through respective type
|
||||
declarations). Interface types only define a set of methods that a
|
||||
corresponding implementation must provide. Thus interface and
|
||||
implementation are strictly separated.
|
||||
|
||||
An interface is implemented by associating methods with
|
||||
structures. If a structure implements all methods of an interface, it
|
||||
implements that interface and thus can be used where that interface is
|
||||
required. Unless used through a variable of interface type, methods
|
||||
can always be statically bound (they are not ``virtual''), and incur no
|
||||
run-time overhead compared to an ordinary function.
|
||||
END]
|
||||
|
||||
Go has no explicit notion of classes, sub-classes, or inheritance.
|
||||
These concepts are trivially modeled in Go through the use of
|
||||
functions, structures, associated methods, and interfaces.
|
||||
|
||||
Go has no explicit notion of type parameters or templates. Instead,
|
||||
containers (such as stacks, lists, etc.) are implemented through the
|
||||
use of abstract operations on interface types or polymorphic values.
|
||||
|
||||
|
||||
Pointers and garbage collection
|
||||
----
|
||||
|
||||
Variables may be allocated automatically (when entering the scope of
|
||||
the variable) or explicitly on the heap. Pointers are used to refer
|
||||
to heap-allocated variables. Pointers may also be used to point to
|
||||
any other variable; such a pointer is obtained by "taking the
|
||||
address" of that variable. Variables are automatically reclaimed when
|
||||
they are no longer accessible. There is no pointer arithmetic in Go.
|
||||
|
||||
|
||||
Multithreading and channels
|
||||
----
|
||||
|
||||
Go supports multithreaded programming directly. A function may
|
||||
be invoked as a parallel thread of execution. Communication and
|
||||
synchronization are provided through channels and their associated
|
||||
language support.
|
||||
|
||||
|
||||
Values and references
|
||||
----
|
||||
|
||||
All objects have value semantics, but their contents may be accessed
|
||||
through different pointers referring to the same object.
|
||||
For example, when calling a function with an array, the array is
|
||||
passed by value, possibly by making a copy. To pass a reference,
|
||||
one must explicitly pass a pointer to the array. For arrays in
|
||||
particular, this is different from C.
|
||||
|
||||
There is also a built-in string type, which represents immutable
|
||||
strings of bytes.
|
||||
|
||||
|
||||
Interface of a type
|
||||
----
|
||||
|
||||
The interface of a type is defined to be the unordered set of methods
|
||||
associated with that type. Methods are defined in a later section;
|
||||
they are functions bound to a type.
|
||||
|
||||
|
||||
[OLD
|
||||
It is legal to assign a pointer to a struct to a variable of
|
||||
compatible interface type. It is legal to assign an interface
|
||||
variable to any struct pointer variable but if the struct type is
|
||||
incompatible the result will be nil.
|
||||
END]
|
||||
|
||||
|
||||
[OLD
|
||||
The polymorphic "any" type
|
||||
----
|
||||
|
||||
Given a variable of type "any", one can store any value into it by
|
||||
plain assignment or implicitly, such as through a function parameter
|
||||
or channel operation. Given an "any" variable v storing an underlying
|
||||
value of type T, one may:
|
||||
|
||||
- copy v's value to another variable of type "any"
|
||||
- extract the stored value by an explicit conversion operation T(v)
|
||||
- copy v's value to a variable of type T
|
||||
|
||||
Attempts to convert/extract to an incompatible type will yield nil.
|
||||
|
||||
No other operations are defined (yet).
|
||||
|
||||
Note that type
|
||||
interface {}
|
||||
is a special case that can match any struct type, while type
|
||||
any
|
||||
can match any type at all, including basic types, arrays, etc.
|
||||
|
||||
TODO: details about reflection
|
||||
END]
|
||||
|
||||
|
||||
[OLD
|
||||
The nil value
|
||||
----
|
||||
|
||||
The predeclared constant
|
||||
|
||||
nil
|
||||
|
||||
represents the ``zero'' value for a pointer type or interface type.
|
||||
|
||||
The only operations allowed for nil are to assign it to a pointer or
|
||||
interface variable and to compare it for equality or inequality with a
|
||||
pointer or interface value.
|
||||
|
||||
var p *int;
|
||||
if p != nil {
|
||||
print(p)
|
||||
} else {
|
||||
print("p points nowhere")
|
||||
}
|
||||
|
||||
By default, pointers are initialized to nil.
|
||||
|
||||
TODO: This needs to be revisited.
|
||||
-->
|
||||
|
||||
Loading…
Reference in New Issue
Block a user