erts: Implement maps path iterator

1 files changed, 130 insertions, 8 deletions

diff --git a/lib/stdlib/doc/src/maps.xml b/lib/stdlib/doc/src/maps.xml
index 8c7270816b..a3afbf8e7f 100644
--- a/lib/stdlib/doc/src/maps.xml
+++ b/lib/stdlib/doc/src/maps.xml
@@ -33,16 +33,32 @@
     <p>This module contains functions for maps processing.</p>
   </description>
 
+  <datatypes>
+    <datatype>
+      <name name="iterator"/>
+      <desc>
+        <p>An iterator representing the key value associations in a map.</p>
+        <p>Created using <seealso marker="#iterator-1"><c>maps:iterator/1</c></seealso>
+        and <seealso marker="#iterator-2"><c>maps:iterator/2</c></seealso>.</p>
+        <p>Consumed by <seealso marker="#next-1"><c>maps:next/1</c></seealso>,
+          <seealso marker="#filter-2"><c>maps:filter/2</c></seealso>,
+          <seealso marker="#fold-3"><c>maps:fold/3</c></seealso> and
+          <seealso marker="#map-2"><c>maps:map/2</c></seealso>.</p>
+      </desc>
+    </datatype>
+  </datatypes>
+
   <funcs>
     <func>
       <name name="filter" arity="2"/>
       <fsummary>Select pairs that satisfy a predicate.</fsummary>
       <desc>
-        <p>Returns a map <c><anno>Map2</anno></c> for which predicate
-          <c><anno>Pred</anno></c> holds true in <c><anno>Map1</anno></c>.</p>
+        <p>Returns a map <c><anno>Map</anno></c> for which predicate
+          <c><anno>Pred</anno></c> holds true in <c><anno>MapOrIter</anno></c>.</p>
         <p>The call fails with a <c>{badmap,Map}</c> exception if
-          <c><anno>Map1</anno></c> is not a map, or with <c>badarg</c> if
-          <c><anno>Pred</anno></c> is not a function of arity 2.</p>
+          <c><anno>MapOrIter</anno></c> is not a map or valid iterator,
+          or with <c>badarg</c> if <c><anno>Pred</anno></c> is not a
+          function of arity 2.</p>
         <p><em>Example:</em></p>
         <code type="none">
 > M = #{a => 2, b => 3, c=> 4, "a" => 1, "b" => 2, "c" => 4},
@@ -76,12 +92,16 @@
       <fsummary></fsummary>
       <desc>
         <p>Calls <c>F(K, V, AccIn)</c> for every <c><anno>K</anno></c> to value
-          <c><anno>V</anno></c> association in <c><anno>Map</anno></c> in
+          <c><anno>V</anno></c> association in <c><anno>MapOrIter</anno></c> in
           any order. Function <c>fun F/3</c> must return a new
           accumulator, which is passed to the next successive call.
           This function returns the final value of the accumulator. The initial
           accumulator value <c><anno>Init</anno></c> is returned if the map is
           empty.</p>
+        <p>The call fails with a <c>{badmap,Map}</c> exception if
+          <c><anno>MapOrIter</anno></c> is not a map or valid iterator,
+          or with <c>badarg</c> if <c><anno>Fun</anno></c> is not a
+          function of arity 3.</p>
         <p><em>Example:</em></p>
         <code type="none">
 > Fun = fun(K,V,AccIn) when is_list(K) -> AccIn + V end,
@@ -169,6 +189,75 @@ false</code>
     </func>
 
     <func>
+      <name name="iterator" arity="1"/>
+      <fsummary>Create a map iterator.</fsummary>
+      <desc>
+        <p>Returns a map iterator <c><anno>Iterator</anno></c> that can
+          be used by <seealso marker="#next-1"><c>maps:next/1</c></seealso>
+          to traverse the keys and values in a map. This call is equivalent
+          to calling <seealso marker="#iterator-2"><c>maps:iterator/2</c></seealso>
+          with an empty map as the options.</p>
+        <p>The call fails with a <c>{badmap,Map}</c> exception if
+          <c><anno>Map</anno></c> is not a map.</p>
+        <p><em>Example:</em></p>
+        <code type="none">
+> M = #{ a => 1, b => 2 }.
+#{a => 1,b => 2}
+> I = maps:iterator(M).
+[{a,1},{b,2}]
+> {K1, V1, I2} = maps:next(I).
+{a,1,[{b,2}]}
+> {K2, V2, I3} = maps:next(I2).
+{b,2,[]}
+> maps:next(I3).
+none</code>
+      </desc>
+    </func>
+
+    <func>
+      <name name="iterator" arity="2"/>
+      <fsummary>Create a map iterator.</fsummary>
+      <desc>
+        <p>Returns a map iterator <c><anno>Iterator</anno></c> that can
+          be used by <seealso marker="#next-1"><c>maps:next/1</c></seealso>
+          to traverse the keys and values in a map. The iterator will behave
+          according to the given <c><anno>Opts</anno></c>.</p>
+        <taglist>
+          <tag>optimize</tag>
+          <item>
+            Configures whether the iterator should be optimized for <c>speed</c>
+            or for <c>memory</c> consumption. Default is <c>speed</c>.
+          </item>
+          <tag>ordered</tag>
+          <item>
+            Configures whether the iterator should return the key value
+            associations ordered on the keys according to erlang term order
+            or not. The default is <c>false</c>.
+          </item>
+        </taglist>
+        <p>Both options can be configured at the same time.</p>
+        <p>The call fails with a <c>{badmap,Map}</c> exception if
+          <c><anno>Map</anno></c> is not a map.</p>
+        <p><em>Example:</em></p>
+        <code type="none">
+> M = maps:from_list([{I,I} || I &lt;- lists:seq(1,50)]).
+#{45 => 45,6 => 6,2 => 2,49 => 49,41 => 41,33 => 33,42 => 42,
+  43 => 43,10 => 10,9 => 9,19 => 19,14 => 14,5 => 5,18 => 18,
+  31 => 31,22 => 22,29 => 29,21 => 21,27 => 27,24 => 24,
+  47 => 47,40 => 40,30 => 30,23 => 23,28 => 28,46 => 46,
+  16 => 16,38 => 38,4 => 4,...}
+> MemoryIter = maps:iterator(M, #{ optimize => memory }), ok.
+ok
+> {K1, V1, _} = maps:next(MemoryIter), {K1, V1}.
+{46,46}
+> OrderedIter = maps:iterator(M, #{ ordered => true, optimize => memory }), ok.
+ok
+> {K2, V2, _} = maps:next(OrderedIter), {K2, V2}.
+{1,1}</code>
+      </desc>
+    </func>
+
+    <func>
       <name name="keys" arity="1"/>
       <fsummary></fsummary>
       <desc>
@@ -188,12 +277,16 @@ false</code>
       <name name="map" arity="2"/>
       <fsummary></fsummary>
       <desc>
-        <p>Produces a new map <c><anno>Map2</anno></c> by calling function
+        <p>Produces a new map <c><anno>Map</anno></c> by calling function
           <c>fun F(K, V1)</c> for every <c><anno>K</anno></c> to value
-          <c><anno>V1</anno></c> association in <c><anno>Map1</anno></c> in
+          <c><anno>V1</anno></c> association in <c><anno>MapOrIter</anno></c> in
           any order. Function <c>fun F/2</c> must return value
           <c><anno>V2</anno></c> to be associated with key <c><anno>K</anno></c>
-          for the new map <c><anno>Map2</anno></c>.</p>
+          for the new map <c><anno>Map</anno></c>.</p>
+        <p>The call fails with a <c>{badmap,Map}</c> exception if
+          <c><anno>MapOrIter</anno></c> is not a map or valid iterator,
+          or with <c>badarg</c> if <c><anno>Fun</anno></c> is not a
+          function of arity 2.</p>
         <p><em>Example:</em></p>
         <code type="none">
 > Fun = fun(K,V1) when is_list(K) -> V1*2 end,
@@ -234,6 +327,35 @@ false</code>
     </func>
 
     <func>
+      <name name="next" arity="1"/>
+      <fsummary>Get the next key and value from an iterator.</fsummary>
+      <desc>
+        <p>Returns the next key-value association in
+          <c><anno>Iterator</anno></c> and a new iterator for the
+          remaining associations in the iterator.
+        </p>
+        <p>
+          If there are no more associations in the iterator,
+          <c>none</c> is returned.
+        </p>
+        <p><em>Example:</em></p>
+        <code type="none">
+> Map = #{a => 1, b => 2, c => 3}.
+#{a => 1,b => 2,c => 3}
+> Iter = maps:iterator(Map).
+[{a,1},{b,2},{c,3}]
+> {_, _, Iter1} = maps:next(Iter).
+{a,1,[{b,2},{c,3}]}
+> {_, _, Iter2} = maps:next(Iter1).
+{b,2,[{c,3}]}
+> {_, _, Iter3} = maps:next(Iter2).
+{c,3,[]}
+> maps:next(Iter3).
+none</code>
+      </desc>
+    </func>
+
+    <func>
       <name name="put" arity="3"/>
       <fsummary></fsummary>
       <desc>