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doc/effective_go.html: a little more about errors

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Make it a little clearer how they are used, in particular that
it is not enough just to return a nil pointer on error, but also
to return an error value explaining the problem.

Fixes #1963.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/97360045
This commit is contained in:
Rob Pike 2014-05-14 13:46:58 -07:00
parent 61d8a33719
commit 1476686cdb
1 changed files with 17 additions and 3 deletions
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20
doc/effective_go.html
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@ -3287,9 +3287,18 @@ the garbage collector for bookkeeping.
<p>
Library routines must often return some sort of error indication to
the caller. As mentioned earlier, Go's multivalue return makes it
the caller.
As mentioned earlier, Go's multivalue return makes it
easy to return a detailed error description alongside the normal
return value. By convention, errors have type <code>error</code>,
return value.
It is good style to use this feature to provide detailed error information.
For example, as we'll see, <code>os.Open</code> doesn't
just return a <code>nil</code> pointer on failure, it also returns an
error value that describes what went wrong.
</p>
<p>
By convention, errors have type <code>error</code>,
a simple built-in interface.
</p>
<pre>
@ -3301,7 +3310,12 @@ type error interface {
A library writer is free to implement this interface with a
richer model under the covers, making it possible not only
to see the error but also to provide some context.
For example, <code>os.Open</code> returns an <code>os.PathError</code>.
As mentioned, alongside the usual <code>*os.File</code>
return value, <code>os.Open</code> also returns an
error value.
If the file is opened successfully, the error will be <code>nil</code>,
but when there is a problem, it will hold an
<code>os.PathError</code>:
</p>
<pre>
// PathError records an error and the operation and