_content/doc/effective_go: remove discussion of loop variable reuse

It's no longer needed as of the Go 1.22 release.

Fixes golang/go#68808

Change-Id: Ib968a414703d28c1d4b4c5300bb5c697264b639e
Reviewed-on: https://go-review.googlesource.com/c/website/+/604575
Reviewed-by: Carlos Amedee <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Rob Pike <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: ianlancetaylor

_content/doc/effective_go.html

@@ -2870,53 +2870,12 @@ <h3 id="channels">Channels</h3>
 of them can run at any moment.
 As a result, the program can consume unlimited resources if the requests come in too fast.
 We can address that deficiency by changing <code>Serve</code> to
-gate the creation of the goroutines.
-Here's an obvious solution, but beware it has a bug we'll fix subsequently:
+gate the creation of the goroutines:
 </p>
 
 <pre>
 func Serve(queue chan *Request) {
     for req := range queue {
-        sem &lt;- 1
-        go func() {
-            process(req) // Buggy; see explanation below.
-            &lt;-sem
-        }()
-    }
-}</pre>
-
-<p>
-The bug is that in a Go <code>for</code> loop, the loop variable
-is reused for each iteration, so the <code>req</code>
-variable is shared across all goroutines.
-That's not what we want.
-We need to make sure that <code>req</code> is unique for each goroutine.
-Here's one way to do that, passing the value of <code>req</code> as an argument
-to the closure in the goroutine:
-</p>
-
-<pre>
-func Serve(queue chan *Request) {
-    for req := range queue {
-        sem &lt;- 1
-        go func(req *Request) {
-            process(req)
-            &lt;-sem
-        }(req)
-    }
-}</pre>
-
-<p>
-Compare this version with the previous to see the difference in how
-the closure is declared and run.
-Another solution is just to create a new variable with the same
-name, as in this example:
-</p>
-
-<pre>
-func Serve(queue chan *Request) {
-    for req := range queue {
-        req := req // Create new instance of req for the goroutine.
         sem &lt;- 1
         go func() {
             process(req)
@@ -2926,22 +2885,13 @@ <h3 id="channels">Channels</h3>
 }</pre>
 
 <p>
-It may seem odd to write
-</p>
-
-<pre>
-req := req
-</pre>
-
-<p>
-but it's legal and idiomatic in Go to do this.
-You get a fresh version of the variable with the same name, deliberately
-shadowing the loop variable locally but unique to each goroutine.
+(Note that in Go versions before 1.22 this code has a bug: the loop
+variable is shared across all goroutines.
+See the <a href="/wiki/LoopvarExperiment">Go wiki</a> for details.)
 </p>
 
 <p>
-Going back to the general problem of writing the server,
-another approach that manages resources well is to start a fixed
+Another approach that manages resources well is to start a fixed
 number of <code>handle</code> goroutines all reading from the request
 channel.
 The number of goroutines limits the number of simultaneous