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Effective Go: update ... discussion.

R=rsc
CC=golang-dev
https://golang.org/cl/1698041
This commit is contained in:
Rob Pike 2010-06-14 22:40:35 -07:00
parent c9172fb2a3
commit 6c08859b0e

View File

@ -423,7 +423,7 @@ if i < f() // wrong!
<h2 id="control-structures">Control structures</h2>
<p>
The control structures of Go are related to those of C but different
The control structures of Go are related to those of C but differ
in important ways.
There is no <code>do</code> or <code>while</code> loop, only a
slightly generalized
@ -1308,22 +1308,24 @@ to print in the format
Our <code>String()</code> method is able to call <code>Sprintf</code> because the
print routines are fully reentrant and can be used recursively.
We can even go one step further and pass a print routine's arguments directly to another such routine.
The signature of <code>Printf</code> uses the <code>...</code>
type for its final argument to specify that an arbitrary number of parameters can appear
after the format.
The signature of <code>Printf</code> uses the type <code>...interface{}</code>
for its final argument to specify that an arbitrary number of parameters (of arbitrary type)
can appear after the format.
</p>
<pre>
func Printf(format string, v ...) (n int, errno os.Error) {
func Printf(format string, v ...interface{}) (n int, errno os.Error) {
</pre>
<p>
Within the function <code>Printf</code>, <code>v</code> is a variable that can be passed,
for instance, to another print routine. Here is the implementation of the
Within the function <code>Printf</code>, <code>v</code> acts like a variable of type
<code>[]interface{}</code> but if it is passed to another variadic function, it acts like
a regular list of arguments.
Here is the implementation of the
function <code>log.Stderr</code> we used above. It passes its arguments directly to
<code>fmt.Sprintln</code> for the actual formatting.
</p>
<pre>
// Stderr is a helper function for easy logging to stderr. It is analogous to Fprint(os.Stderr).
func Stderr(v ...) {
func Stderr(v ...interface{}) {
stderr.Output(2, fmt.Sprintln(v)) // Output takes parameters (int, string)
}
</pre>
@ -1331,6 +1333,21 @@ func Stderr(v ...) {
There's even more to printing than we've covered here. See the <code>godoc</code> documentation
for package <code>fmt</code> for the details.
</p>
<p>
By the way, a <code>...</code> parameter can be of a specific type, for instance <code>...int</code>
for a min function that chooses the least of a list of integers:
</p>
<pre>
func Min(a ...int) int {
min := int(^uint(0) >> 1) // largest int
for _, i := range a {
if i < min {
min = i
}
}
return min
}
</pre>
<h2 id="initialization">Initialization</h2>
@ -1948,7 +1965,7 @@ type Job struct {
<p>
The <code>Job</code> type now has the <code>Log</code>, <code>Logf</code>
and other
methods of <code>log.Logger</code>. We could have given the <code>Logger</code>
methods of <code>*log.Logger</code>. We could have given the <code>Logger</code>
a field name, of course, but it's not necessary to do so. And now, once
initialized, we can
log to the <code>Job</code>:
@ -1993,7 +2010,7 @@ of <code>Job</code> would dominate it.
</p>
<p>
Second, if the same name appears at the same nesting level, it is usually an error;
it would be erroneous to embed <code>log.Logger</code> if <code>Job</code> struct
it would be erroneous to embed <code>log.Logger</code> if the <code>Job</code> struct
contained another field or method called <code>Logger</code>.
However, if the duplicate name is never mentioned in the program outside the type definition, it is OK.
This qualification provides some protection against changes made to types embedded from outside; there