/src/mochilists.erl

  1%% @copyright Copyright (c) 2010 Mochi Media, Inc.
  2%% @author David Reid <dreid@mochimedia.com>
  3%%
  4%% Permission is hereby granted, free of charge, to any person obtaining a
  5%% copy of this software and associated documentation files (the "Software"),
  6%% to deal in the Software without restriction, including without limitation
  7%% the rights to use, copy, modify, merge, publish, distribute, sublicense,
  8%% and/or sell copies of the Software, and to permit persons to whom the
  9%% Software is furnished to do so, subject to the following conditions:
 10%%
 11%% The above copyright notice and this permission notice shall be included in
 12%% all copies or substantial portions of the Software.
 13%%
 14%% THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 15%% IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 16%% FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 17%% THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 18%% LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 19%% FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 20%% DEALINGS IN THE SOFTWARE.
 21
 22%% @doc Utility functions for dealing with proplists.
 23
 24-module(mochilists).
 25-author("David Reid <dreid@mochimedia.com>").
 26-export([get_value/2, get_value/3, is_defined/2, set_default/2, set_defaults/2]).
 27
 28%% @spec set_default({Key::term(), Value::term()}, Proplist::list()) -> list()
 29%%
 30%% @doc Return new Proplist with {Key, Value} set if not is_defined(Key, Proplist).
 31set_default({Key, Value}, Proplist) ->
 32    case is_defined(Key, Proplist) of
 33        true ->
 34            Proplist;
 35        false ->
 36            [{Key, Value} | Proplist]
 37    end.
 38
 39%% @spec set_defaults([{Key::term(), Value::term()}], Proplist::list()) -> list()
 40%%
 41%% @doc Return new Proplist with {Key, Value} set if not is_defined(Key, Proplist).
 42set_defaults(DefaultProps, Proplist) ->
 43    lists:foldl(fun set_default/2, Proplist, DefaultProps).
 44
 45
 46%% @spec is_defined(Key::term(), Proplist::list()) -> bool()
 47%%
 48%% @doc Returns true if Propist contains at least one entry associated
 49%%      with Key, otherwise false is returned.
 50is_defined(Key, Proplist) ->
 51    lists:keyfind(Key, 1, Proplist) =/= false.
 52
 53
 54%% @spec get_value(Key::term(), Proplist::list()) -> term() | undefined
 55%%
 56%% @doc Return the value of <code>Key</code> or undefined
 57get_value(Key, Proplist) ->
 58    get_value(Key, Proplist, undefined).
 59
 60%% @spec get_value(Key::term(), Proplist::list(), Default::term()) -> term()
 61%%
 62%% @doc Return the value of <code>Key</code> or <code>Default</code>
 63get_value(_Key, [], Default) ->
 64    Default;
 65get_value(Key, Proplist, Default) ->
 66    case lists:keyfind(Key, 1, Proplist) of
 67        false ->
 68            Default;
 69        {Key, Value} ->
 70            Value
 71    end.
 72
 73%%
 74%% Tests
 75%%
 76-ifdef(TEST).
 77-include_lib("eunit/include/eunit.hrl").
 78
 79set_defaults_test() ->
 80    ?assertEqual(
 81       [{k, v}],
 82       set_defaults([{k, v}], [])),
 83    ?assertEqual(
 84       [{k, v}],
 85       set_defaults([{k, vee}], [{k, v}])),
 86    ?assertEqual(
 87       lists:sort([{kay, vee}, {k, v}]),
 88       lists:sort(set_defaults([{k, vee}, {kay, vee}], [{k, v}]))),
 89    ok.
 90
 91set_default_test() ->
 92    ?assertEqual(
 93       [{k, v}],
 94       set_default({k, v}, [])),
 95    ?assertEqual(
 96       [{k, v}],
 97       set_default({k, vee}, [{k, v}])),
 98    ok.
 99
100get_value_test() ->
101    ?assertEqual(
102       undefined,
103       get_value(foo, [])),
104    ?assertEqual(
105       undefined,
106       get_value(foo, [{bar, baz}])),
107    ?assertEqual(
108       bar,
109       get_value(foo, [{foo, bar}])),
110    ?assertEqual(
111       default,
112       get_value(foo, [], default)),
113    ?assertEqual(
114       default,
115       get_value(foo, [{bar, baz}], default)),
116    ?assertEqual(
117       bar,
118       get_value(foo, [{foo, bar}], default)),
119    ok.
120
121-endif.
122