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authorSverker Eriksson <[email protected]>2017-05-05 14:51:58 +0200
committerSverker Eriksson <[email protected]>2017-05-10 11:46:10 +0200
commit6c3265b86582d4848e1c77efee3a649a137694d6 (patch)
tree876267fdaa055bdb204a77127d3a9f4c5f137d4d /lib/stdlib
parent95dec7497abbdb06defcb23e99fa31e06597496e (diff)
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stdlib: Add examples for ets:select_replace docs
Diffstat (limited to 'lib/stdlib')
-rw-r--r--lib/stdlib/doc/src/ets.xml36
1 files changed, 28 insertions, 8 deletions
diff --git a/lib/stdlib/doc/src/ets.xml b/lib/stdlib/doc/src/ets.xml
index d1ec176f81..62e97218cd 100644
--- a/lib/stdlib/doc/src/ets.xml
+++ b/lib/stdlib/doc/src/ets.xml
@@ -1495,17 +1495,37 @@ is_integer(X), is_integer(Y), X + Y < 4711]]></code>
<fsummary>Match and replace objects atomically in an ETS table</fsummary>
<desc>
<p>Matches the objects in the table <c><anno>Tab</anno></c> using a
- <seealso marker="#match_spec">match specification</seealso>. If
- an object is matched, the existing object is replaced with
- the match specification result, which <em>must</em> retain
- the original key or the operation will fail with <c>badarg</c>.</p>
+ <seealso marker="#match_spec">match specification</seealso>. For each
+ matched object, the existing object is replaced with
+ the match specification result.</p>
+ <p>The match-and-replace operation for each individual object is guaranteed to be
+ <seealso marker="#concurrency">atomic and isolated</seealso>. The
+ <c>select_replace</c> table iteration as a whole, like all other select functions,
+ does not give such guarantees.</p>
+ <p>The match specifiction must be guaranteed to <em>retain the key</em>
+ of any matched object. If not, <c>select_replace</c> will fail with <c>badarg</c>
+ without updating any objects.</p>
<p>For the moment, due to performance and semantic constraints,
tables of type <c>bag</c> are not yet supported.</p>
<p>The function returns the total number of replaced objects.</p>
- <note>
- <p>The match/replacement operation atomicity scope is limited
- to each individual object.</p>
- </note>
+ <p><em>Example</em></p>
+ <p>For all 2-tuples with a list in second position, add atom <c>'marker'</c> first in the list:</p>
+ <pre>
+1> <input>T = ets:new(x,[]), ets:insert(T, {key, [1, 2, 3]}).</input>
+true
+2> <input>MS = ets:fun2ms(fun({K, L}) when is_list(L) -> {K, [marker | L]} end).</input>
+[{{'$1','$2'},[{is_list,'$2'}],[{{'$1',[marker|'$2']}}]}]
+3> <input>ets:select_replace(T, MS).</input>
+1
+4> <input>ets:tab2list(T).</input>
+[{key,[marker,1,2,3]}]
+ </pre>
+ <p>A generic single object compare-and-swap operation:</p>
+ <pre>
+[Old] = ets:lookup(T, Key),
+New = update_object(Old),
+Success = (1 =:= ets:select_replace(T, [{Old, [], [{const, New}]}])),
+ </pre>
</desc>
</func>