Commit 49a35a63 authored by Rob Pike's avatar Rob Pike

be more explicit about initialization of embedded fields.

R=rsc
CC=golang-dev
https://golang.org/cl/186161
parent 8cf627ad
......@@ -1395,7 +1395,7 @@ func (b ByteSize) String() string {
</pre>
<p>
The expression <code>YB</code> prints as <code>1.00YB</code>,
while <code>ByteSize(1e13)</code> prints as <code>9.09TB</code>,
while <code>ByteSize(1e13)</code> prints as <code>9.09TB</code>.
</p>
<h3 id="variables">Variables</h3>
......@@ -1878,12 +1878,15 @@ but does not give them field names.
// ReadWriter stores pointers to a Reader and a Writer.
// It implements io.ReadWriter.
type ReadWriter struct {
*Reader
*Writer
*Reader // *bufio.Reader
*Writer // *bufio.Writer
}
</pre>
<p>
This struct could be written as
The embedded elements are pointers to structs and of course
must be initialized to point to valid structs before they
can be used.
The <code>ReadWriter</code> struct could be written as
</p>
<pre>
type ReadWriter struct {
......@@ -1933,15 +1936,16 @@ type Job struct {
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>
a field name, of course, but it's not necessary to do so. And now we can
log to a <code>Job</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>:
</p>
<pre>
job.Log("starting now...")
</pre>
<p>
The <code>Logger</code> is a regular field of the struct and we can initialize
it in the usual way.
it in the usual way with a constructor,
</p>
<pre>
func NewJob(command string, logger *log.Logger) *Job {
......@@ -1949,6 +1953,12 @@ func NewJob(command string, logger *log.Logger) *Job {
}
</pre>
<p>
or with a composite literal,
</p>
<pre>
job := &amp;Job{command, log.New(os.Stderr, nil, "Job: ", log.Ldate)}
</pre>
<p>
If we need to refer to an embedded field directly, the type name of the field,
ignoring the package qualifier, serves as a field name. If we needed to access the
<code>*log.Logger</code> of a <code>Job</code> variable <code>job</code>,
......
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