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Diffstat (limited to 'doc/go_tutorial.txt')
| -rw-r--r-- | doc/go_tutorial.txt | 58 |
1 files changed, 28 insertions, 30 deletions
diff --git a/doc/go_tutorial.txt b/doc/go_tutorial.txt index 89ac59fa1..164182030 100644 --- a/doc/go_tutorial.txt +++ b/doc/go_tutorial.txt @@ -4,7 +4,7 @@ Let's Go Rob Pike ---- -(March 17, 2009) +(March 18, 2009) This document is a tutorial introduction to the basics of the Go systems programming @@ -36,7 +36,9 @@ Let's start in the usual way: Every Go source file declares, using a "package" statement, which package it's part of. The "main" package's "main" function is where the program starts running (after -any initialization). +any initialization). It may also import other packages to use their facilities. +This program imports the package "fmt" to gain access to +our old, now capitalized and package-qualified friend, "fmt.Printf". Function declarations are introduced with the "func" keyword. @@ -44,18 +46,6 @@ Notice that string constants can contain Unicode characters, encoded in UTF-8. Go is defined to accept UTF-8 input. Strings are arrays of bytes, usually used to store Unicode strings represented in UTF-8. -The built-in function "print()" has been used during the early stages of -development of the language but is not guaranteed to last. Here's a version of the -program that doesn't depend on "print()": - ---PROG progs/helloworld2.go - -This version imports the ''os'' package to acess its "Stdout" variable, of type -"*os.File". The "import" statement is a declaration: it names the identifier ("os") -that will be used to access members of the package imported from the file ("os"), -found in the current directory or in a standard location. -Given "os.Stdout" we can use its "WriteString" method to print the string. - The comment convention is the same as in C++: /* ... */ @@ -84,12 +74,23 @@ Semicolons aren't needed here; in fact, semicolons are unnecessary after any top-level declaration, even though they are needed as separators <i>within</i> a parenthesized list of declarations. -Also notice that we've dropped the explicit name from the imports; by default, +This program imports the ""os"" package to access its "Stdout" variable, of type +"*os.File". The "import" statement is actually a declaration: in its general form, +as used in our ``hello world'' program, +it names the identifier ("fmt") +that will be used to access members of the package imported from the file (""fmt""), +found in the current directory or in a standard location. +In this program, though, we've dropped the explicit name from the imports; by default, packages are imported using the name defined by the imported package, -which by convention is of course the file name itself. You can specify your +which by convention is of course the file name itself. Our ``hello world'' program +could have said just "import "fmt"". + +You can specify your own import names if you want but it's only necessary if you need to resolve a naming conflict. +Given "os.Stdout" we can use its "WriteString" method to print the string. + Having imported the "flag" package, line 8 creates a global variable to hold the value of echo's "-n" flag. The variable "n_flag" has type "*bool", pointer to "bool". @@ -407,7 +408,7 @@ Finally, we can use our new package: --PROG progs/helloworld3.go -and run the program: +And now we can run the program: % helloworld3 hello, world @@ -424,8 +425,8 @@ Building on the "file" package, here's a simple version of the Unix utility "cat By now this should be easy to follow, but the "switch" statement introduces some new features. Like a "for" loop, an "if" or "switch" can include an -initialization statement. The "switch" on line 12 uses one to create variables -"nr" and "er" to hold the return values from "f.Read()". (The "if" on line 19 +initialization statement. The "switch" on line 14 uses one to create variables +"nr" and "er" to hold the return values from "f.Read()". (The "if" on line 21 has the same idea.) The "switch" statement is general: it evaluates the cases from top to bottom looking for the first case that matches the value; the case expressions don't need to be constants or even integers, as long as @@ -437,7 +438,7 @@ in a "for" statement, a missing value means "true". In fact, such a "switch" is a form of "if-else" chain. While we're here, it should be mentioned that in "switch" statements each "case" has an implicit "break". -Line 19 calls "Write()" by slicing the incoming buffer, which is itself a slice. +Line 21 calls "Write()" by slicing the incoming buffer, which is itself a slice. Slices provide the standard Go way to handle I/O buffers. Now let's make a variant of "cat" that optionally does "rot13" on its input. @@ -462,7 +463,7 @@ we have a second implementation of the "reader" interface. --PROG progs/cat_rot13.go /type.rotate13/ /end.of.rotate13/ -(The "rot13" function called on line 37 is trivial and not worth reproducing.) +(The "rot13" function called on line 38 is trivial and not worth reproducing.) To use the new feature, we define a flag: @@ -474,7 +475,7 @@ and use it from within a mostly unchanged "cat()" function: (We could also do the wrapping in "main" and leave "cat()" mostly alone, except for changing the type of the argument; consider that an exercise.) -Lines 51 through 53 set it all up: If the "rot13" flag is true, wrap the "reader" +Lines 52 through 55 set it all up: If the "rot13" flag is true, wrap the "reader" we received into a "rotate13" and proceed. Note that the interface variables are values, not pointers: the argument is of type "reader", not "*reader", even though under the covers it holds a pointer to a "struct". @@ -551,11 +552,8 @@ Printing The examples of formatted printing so far have been modest. In this section we'll talk about how formatted I/O can be done well in Go. -There's a package "fmt" that implements a version of "Printf" (upper case) -that should look familiar: - ---PROG progs/printf.go - +We've seen simple uses of the package "fmt", which +implements "Printf", "Fprintf", and so on. Within the "fmt" package, "Printf" is declared with this signature: Printf(format string, v ...) (n int, errno *os.Error) @@ -740,7 +738,7 @@ together: --PROG progs/sieve.go /func.main/ /^}/ -Line 23 creates the initial channel to pass to "generate", which it +Line 25 creates the initial channel to pass to "generate", which it then starts up. As each prime pops out of the channel, a new "filter" is added to the pipeline and <i>its</i> output becomes the new value of "ch". @@ -756,7 +754,7 @@ channel, launches a goroutine internally using a function literal, and returns the channel to the caller. It is a factory for concurrent execution, starting the goroutine and returning its connection. -The function literal notation (lines 6-10) allows us to construct an +The function literal notation (lines 8-12) allows us to construct an anonymous function and invoke it on the spot. The same change can be made to "filter": @@ -789,7 +787,7 @@ code that invokes the operation and responds to the request: --PROG progs/server.go /type.binOp/ /^}/ -Line 8 defines the name "binOp" to be a function taking two integers and +Line 10 defines the name "binOp" to be a function taking two integers and returning a third. The "server" routine loops forever, receiving requests and, to avoid blocking due to |