diff options
Diffstat (limited to 'doc/go_tutorial.txt')
| -rw-r--r-- | doc/go_tutorial.txt | 24 |
1 files changed, 19 insertions, 5 deletions
diff --git a/doc/go_tutorial.txt b/doc/go_tutorial.txt index 2b2a0cda1..ab02baf2c 100644 --- a/doc/go_tutorial.txt +++ b/doc/go_tutorial.txt @@ -384,8 +384,8 @@ assigned to a variable. An I/O Package ---- -Next we'll look at a simple package for doing file I/O with the usual -sort of open/close/read/write interface. Here's the start of "file.go": +Next we'll look at a simple package for doing file I/O with an +open/close/read/write interface. Here's the start of "file.go": --PROG progs/file.go /package/ /^}/ @@ -437,11 +437,11 @@ We can use the factory to construct some familiar, exported variables of type "* --PROG progs/file.go /var/ /^.$/ The "newFile" function was not exported because it's internal. The proper, -exported factory to use is "Open": +exported factory to use is "OpenFile" (we'll explain that name in a moment): ---PROG progs/file.go /func.Open/ /^}/ +--PROG progs/file.go /func.OpenFile/ /^}/ -There are a number of new things in these few lines. First, "Open" returns +There are a number of new things in these few lines. First, "OpenFile" returns multiple values, a "File" and an error (more about errors in a moment). We declare the multi-value return as a parenthesized list of declarations; syntactically @@ -460,6 +460,20 @@ consistent error handling throughout Go code. In "Open" we use a conversion to translate Unix's integer "errno" value into the integer type "os.Errno", which implements "os.Error". +Why "OpenFile" and not "Open"? To mimic Go's "os" package, which +our exercise is emulating. The "os" package takes the opportunity +to make the two commonest cases - open for read and create for +write - the simplest, just "Open" and "Create". "OpenFile" is the +general case, analogous to the Unix system call "Open". Here is +the implementation of our "Open" and "Create"; they're trivial +wrappers that eliminate common errors by capturing +the tricky standard arguments to open and, especially, to create a file: + +--PROG progs/file.go /^const/ /^}/ + +--PROG progs/file.go /func.Create/ /^}/ + +Back to our main story. Now that we can build "Files", we can write methods for them. To declare a method of a type, we define a function to have an explicit receiver of that type, placed |