Add convenience function json2:obj_fetch/3

The json2:obj_fetch/2 either returns an object member's value or exits
with a struct_no_key error if the object member is not found. Add
json2:obj_fetch/3 that returns either the object member's value or a
default value if the object member is not found.

Add a new unit test for json2:obj_fetch/2,3 to the json2_SUITE.

Also in json2_SUITE, fix the test source directories for the
json2_decode_valid and json2_decode_invalid tests. Add asserts to
verify that one or more test files are processed by those tests.

src/json2.erl

@@ -16,7 +16,7 @@
 
 -module(json2).
 -export([encode/1, decode_string/1, decode/2]).
--export([is_obj/1, obj_new/0, obj_fetch/2, obj_find/2, obj_is_key/2]).
+-export([is_obj/1, obj_new/0, obj_fetch/2, obj_fetch/3, obj_find/2, obj_is_key/2]).
 -export([obj_store/3, obj_from_list/1, obj_fold/3]).
 -export([test/0]).
 -author("Jim Larson <jalarson@amazon.com>, Robert Wai-Chi Chu <robchu@amazon.com>").
@@ -597,7 +597,7 @@ obj_new() ->
     {struct, []}.
 
 %% Fetch an object member's value, expecting it to be in the object.
-%% Return value, runtime error if no member found with that name.
+%% Return value, or runtime error if no member found with that name.
 
 obj_fetch(Key, {struct, Props}) when is_list(Props) ->
     case proplists:get_value(Key, Props) of
@@ -607,6 +607,19 @@ obj_fetch(Key, {struct, Props}) when is_list(Props) ->
             Value
     end.
 
+
+%% Fetch an object member's value if the member exists. Return value
+%% if found, or default if no member found with that name.
+
+obj_fetch(Key, {struct, Props}, Default) when is_list(Props) ->
+    case proplists:get_value(Key, Props) of
+        undefined ->
+            Default;
+        Value ->
+            Value
+    end.
+
+
 %% Fetch an object member's value, or indicate that there is no such member.
 %% Return {ok, Value} or 'error'.
 

testsuite/json2_SUITE.erl

@@ -8,7 +8,8 @@ all() ->
     [
      json2_decode_valid,
      json2_decode_invalid,
-     json2_decode_invalid_utf8
+     json2_decode_invalid_utf8,
+     json2_obj_fetch
     ].
 
 groups() ->
@@ -36,8 +37,9 @@ end_per_testcase(_Test, _Config) ->
 
 %%====================================================================
 json2_decode_valid(_Config) ->
-    Dir = filename:join(?srcdir, "json2_SUITE_data/valid"),
+    Dir = filename:join(?data_srcdir(?MODULE), "valid"),
     Tests = filelib:wildcard(filename:join(Dir, "*.json")),
+    ?assertMatch([_|_], Tests),
     [begin
          {ok, Bin} = file:read_file(T),
          Str = unicode:characters_to_list(Bin),
@@ -46,8 +48,9 @@ json2_decode_valid(_Config) ->
     ok.
 
 json2_decode_invalid(_Config) ->
-    Dir = filename:join(?srcdir, "json2_SUITE_data/invalid"),
+    Dir = filename:join(?data_srcdir(?MODULE), "invalid"),
     Tests = filelib:wildcard(filename:join(Dir, "*.json")),
+    ?assertMatch([_|_], Tests),
     [begin
          {ok, Bin} = file:read_file(T),
          Str = unicode:characters_to_list(Bin),
@@ -61,3 +64,19 @@ json2_decode_invalid_utf8(_Config) ->
     ?assertMatch({Str1, {error, _}}, {Str1, json2:decode_string(Str1)}),
     ?assertMatch({Str2, {error, _}}, {Str2, json2:decode_string(Str2)}),
     ok.
+
+json2_obj_fetch(_Config) ->
+    F = filename:join(?data_srcdir(?MODULE), "valid/simple-object.json"),
+    {ok, Bin} = file:read_file(F),
+    Str = unicode:characters_to_list(Bin),
+    {ok, Obj} = json2:decode_string(Str),
+    ?assertEqual({array,[]}, json2:obj_fetch("a", Obj)),
+    NotFound = try
+                   json2:obj_fetch("b", Obj)
+               catch
+                   C:Exc ->
+                       {C, Exc}
+               end,
+    ?assertEqual({exit, {struct_no_key, "b"}}, NotFound),
+    ?assertEqual(foo, json2:obj_fetch("b", Obj, foo)),
+    ok.