-chan T // can send and receive values of type T +chan T // can be used to send and receive values of type T chan <- float // can only be used to send floats -<-chan int // can only receive ints +<-chan int // can only be used to receive ints
@@ -3065,27 +3065,6 @@ if x := f(); x < y { - -
@@ -3757,81 +3736,154 @@ m := make(map[string] int, 100); # map with initial space for 100 elements
+Go programs are constructed by linking together packages. +A package is in turn constructed from one or more source files that +together provide an interface to a set of types, constants, functions, +and variables. Those elements may be imported and used in +another package. +
+ ++Each source file consists of a package clause defining the package +to which it belongs, followed by a possibly empty set of import +declarations that declare packages whose contents it wishes to use, +followed by a possibly empty set of declarations of functions, +types, variables, and constants. The source text following the +package clause acts as a block for scoping ($Declarations and scope +rules). +
-Package = PackageClause { ImportDecl [ ";" ] } { Declaration [ ";" ] } .
+SourceFile = PackageClause { ImportDecl [ ";" ] } { Declaration [ ";" ] } .
-The source text following the package clause acts like a block for scoping
-purposes ($Declarations and scope rules).
+-Every source file identifies the package to which it belongs. -The file must begin with a package clause. +A package clause begins each source file and defines the package +to which the file belongs. +
-PackageClause = "package" PackageName . - -package Math +PackageClause = "package" PackageName .+
+package math +-A package can gain access to exported identifiers from another package -through an import declaration: +
+A set of files sharing the same PackageName form the implementation of a package. +An implementation may require that all source files for a package inhabit the same directory. +
+ ++A source file gains access to exported identifiers (§Exported +identifiers) from another package through an import declaration. +In the general form, an import declaration provides an identifier +that code in the source file may use to access the imported package's +contents and a file name referring to the (compiled) implementation of +the package. The file name may be relative to a repository of +installed packages. +
-ImportDecl = "import" ( ImportSpec | "(" [ ImportSpecList ] ")" ) .
-ImportSpecList = ImportSpec { ";" ImportSpec } [ ";" ] .
-ImportSpec = [ "." | PackageName ] PackageFileName .
-PackageFileName = StringLit .
+ImportDecl = "import" ( ImportSpec | "(" [ ImportSpecList ] ")" ) .
+ImportSpecList = ImportSpec { ";" ImportSpec } [ ";" ] .
+ImportSpec = [ "." | PackageName ] PackageFileName .
+PackageFileName = StringLit .
-An import statement makes the exported package-level identifiers of the named
-package file accessible to this package.
-In the following discussion, assume we have a package in the
-file "/lib/math", called package "math", which exports the identifiers
-"Sin" and "Cos" denoting the respective trigonometric functions.
+After an import, in the usual case an exported name N from the imported
+package P may be accessed by the qualified identifier
+P.N (§Qualified identifiers). The actual
+name P depends on the form of the import declaration. If
+an explicit package name p1 is provided, the qualified
+identifer will have the form p1.N. If no name
+is provided in the import declaration, P will be the package
+name declared within the source files of the imported package.
+Finally, if the import declaration uses an explicit period
+(.) for the package name, N will appear
+in the package-level scope of the current file and the qualified name is
+unnecessary and erroneous. In this form, it is an error if the import introduces
+a name conflict.
+
-In the general form, with an explicit package name, the import
-statement declares that package name as an identifier whose
-contents are the exported elements of the imported package.
-For instance, after
+In this table, assume we have compiled a package named
+math, which exports function Sin, and
+installed the compiled package in file
+"lib/math".
+
+Import syntax Local name of Sin + +import M "lib/math" M.Sin +import "lib/math" math.Sin +import . "lib/math" Sin ++ +
+If a package is constructed from multiple source files, all names +at package-level scope, not just exported names, are visible to all the +files in the package. An import declaration is still necessary to +declare intention to use the names, +but the imported names do not need a qualified identifer to be +accessed. +
+ ++The compilation of a multi-file package may require +that the files be compiled and installed in an order that satisfies +the resolution of names imported within the package. +
+ +
+If source file math1.go contains
+
-import M "/lib/math"
+package math
+
+const twoPi = 6.283185307179586
+
+function Sin(x float) float { return ... }
-the contents of the package /lib/math can be accessed by
-"M.Sin", "M.Cos", etc.
-In its simplest form, with no package name, the import statement
-implicitly uses the imported package name itself as the local
-package name. After
-
+and file "math2.go" begins
+
-import "/lib/math" +package math + +import "lib/math"-the contents are accessible by "math.Sin", "math.Cos".
-Finally, if instead of a package name the import statement uses
-an explicit period, the contents of the imported package are added
-to the current package. After
+then, provided "math1.go" is compiled first and
+installed in "lib/math", math2.go
+may refer directly to Sin and twoPi
+without a qualified identifier.
+
-import . "/lib/math" -+
-Here is a complete example Go package that implements a concurrent prime sieve: +Here is a complete Go package that implements a concurrent prime sieve. +
package main
+import "fmt"
+
// Send the sequence 2, 3, 4, ... to channel 'ch'.
func generate(ch chan <- int) {
for i := 2; ; i++ {
@@ -3856,7 +3908,7 @@ func sieve() {
go generate(ch); // Start generate() as a subprocess.
for {
prime := <-ch;
- print(prime, "\n");
+ fmt.Print(prime, "\n");
ch1 := make(chan int);
go filter(ch, ch1, prime);
ch = ch1
@@ -3972,7 +4024,7 @@ Program execution begins by initializing the main package and then
invoking main.main().
-When main.main() returns, the program exits.
+When main.main() returns, the program exits.