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Effective Go: update ... discussion.
R=rsc CC=golang-dev https://golang.org/cl/1698041
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@ -245,7 +245,7 @@ var (
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countLock sync.Mutex
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countLock sync.Mutex
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inputCount uint32
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inputCount uint32
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outputCount uint32
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outputCount uint32
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errorCount uint32
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errorCount uint32
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)
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)
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</pre>
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</pre>
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@ -423,7 +423,7 @@ if i < f() // wrong!
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<h2 id="control-structures">Control structures</h2>
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<h2 id="control-structures">Control structures</h2>
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<p>
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<p>
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The control structures of Go are related to those of C but different
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The control structures of Go are related to those of C but differ
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in important ways.
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in important ways.
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There is no <code>do</code> or <code>while</code> loop, only a
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There is no <code>do</code> or <code>while</code> loop, only a
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slightly generalized
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slightly generalized
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@ -1308,22 +1308,24 @@ to print in the format
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Our <code>String()</code> method is able to call <code>Sprintf</code> because the
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Our <code>String()</code> method is able to call <code>Sprintf</code> because the
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print routines are fully reentrant and can be used recursively.
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print routines are fully reentrant and can be used recursively.
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We can even go one step further and pass a print routine's arguments directly to another such routine.
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We can even go one step further and pass a print routine's arguments directly to another such routine.
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The signature of <code>Printf</code> uses the <code>...</code>
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The signature of <code>Printf</code> uses the type <code>...interface{}</code>
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type for its final argument to specify that an arbitrary number of parameters can appear
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for its final argument to specify that an arbitrary number of parameters (of arbitrary type)
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after the format.
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can appear after the format.
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</p>
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</p>
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<pre>
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<pre>
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func Printf(format string, v ...) (n int, errno os.Error) {
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func Printf(format string, v ...interface{}) (n int, errno os.Error) {
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</pre>
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</pre>
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<p>
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<p>
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Within the function <code>Printf</code>, <code>v</code> is a variable that can be passed,
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Within the function <code>Printf</code>, <code>v</code> acts like a variable of type
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for instance, to another print routine. Here is the implementation of the
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<code>[]interface{}</code> but if it is passed to another variadic function, it acts like
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a regular list of arguments.
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Here is the implementation of the
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function <code>log.Stderr</code> we used above. It passes its arguments directly to
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function <code>log.Stderr</code> we used above. It passes its arguments directly to
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<code>fmt.Sprintln</code> for the actual formatting.
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<code>fmt.Sprintln</code> for the actual formatting.
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</p>
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</p>
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<pre>
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<pre>
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// Stderr is a helper function for easy logging to stderr. It is analogous to Fprint(os.Stderr).
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// Stderr is a helper function for easy logging to stderr. It is analogous to Fprint(os.Stderr).
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func Stderr(v ...) {
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func Stderr(v ...interface{}) {
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stderr.Output(2, fmt.Sprintln(v)) // Output takes parameters (int, string)
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stderr.Output(2, fmt.Sprintln(v)) // Output takes parameters (int, string)
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}
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}
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</pre>
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</pre>
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@ -1331,6 +1333,21 @@ func Stderr(v ...) {
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There's even more to printing than we've covered here. See the <code>godoc</code> documentation
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There's even more to printing than we've covered here. See the <code>godoc</code> documentation
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for package <code>fmt</code> for the details.
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for package <code>fmt</code> for the details.
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</p>
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</p>
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<p>
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By the way, a <code>...</code> parameter can be of a specific type, for instance <code>...int</code>
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for a min function that chooses the least of a list of integers:
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</p>
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<pre>
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func Min(a ...int) int {
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min := int(^uint(0) >> 1) // largest int
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for _, i := range a {
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if i < min {
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min = i
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}
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}
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return min
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}
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</pre>
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<h2 id="initialization">Initialization</h2>
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<h2 id="initialization">Initialization</h2>
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@ -1948,7 +1965,7 @@ type Job struct {
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<p>
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<p>
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The <code>Job</code> type now has the <code>Log</code>, <code>Logf</code>
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The <code>Job</code> type now has the <code>Log</code>, <code>Logf</code>
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and other
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and other
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methods of <code>log.Logger</code>. We could have given the <code>Logger</code>
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methods of <code>*log.Logger</code>. We could have given the <code>Logger</code>
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a field name, of course, but it's not necessary to do so. And now, once
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a field name, of course, but it's not necessary to do so. And now, once
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initialized, we can
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initialized, we can
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log to the <code>Job</code>:
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log to the <code>Job</code>:
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@ -1993,7 +2010,7 @@ of <code>Job</code> would dominate it.
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</p>
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</p>
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<p>
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<p>
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Second, if the same name appears at the same nesting level, it is usually an error;
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Second, if the same name appears at the same nesting level, it is usually an error;
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it would be erroneous to embed <code>log.Logger</code> if <code>Job</code> struct
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it would be erroneous to embed <code>log.Logger</code> if the <code>Job</code> struct
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contained another field or method called <code>Logger</code>.
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contained another field or method called <code>Logger</code>.
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However, if the duplicate name is never mentioned in the program outside the type definition, it is OK.
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However, if the duplicate name is never mentioned in the program outside the type definition, it is OK.
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This qualification provides some protection against changes made to types embedded from outside; there
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This qualification provides some protection against changes made to types embedded from outside; there
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