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-module(klsn_map). |
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-export([ |
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lookup/2 |
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, get/2 |
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, get/3 |
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, upsert/3 |
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, remove/2 |
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, filter/1 |
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, invert/1 |
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]). |
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-export_type([ |
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key/0 |
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]). |
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%% A path into a nested map, represented as a list of keys. Example: |
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%% [foo, bar, baz] first looks up foo in the outer map, then bar in |
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%% the returned map, and finally baz. |
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-type key() :: [term()]. |
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%% @doc |
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%% Fetch the value at Key inside Map or raise error:not_found when |
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%% the path cannot be resolved. |
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-spec get(key(), map()) -> term(). |
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get(Key, Map) -> |
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case lookup(Key, Map) of |
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{value, Value} -> |
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Value; |
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none -> |
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erlang:error(not_found, [Key, Map]) |
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end. |
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|
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%% @doc |
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%% Same as get/2 but returns Default instead of throwing. |
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-spec get(key(), map(), term()) -> term(). |
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get(Key, Map, Default) -> |
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klsn_maybe:get_value(lookup(Key, Map), Default). |
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|
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%% @doc |
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%% Variant of get/2 that never throws. Returns {value, V} when the |
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%% path exists or none otherwise. |
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-spec lookup(key(), map()) -> klsn:'maybe'(term()). |
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lookup([], Value) -> |
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{value, Value}; |
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lookup(_, Value) when not is_map(Value) -> |
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none; |
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lookup([H|T], Map) -> |
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case maps:find(H, Map) of |
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{ok, Value} -> |
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lookup(T, Value); |
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error -> |
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none |
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end. |
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%% @doc |
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%% Insert or replace the element located at *Key* with *Value* inside |
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%% *Map*. Missing intermediary maps are created on-the-fly. |
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-spec upsert(key(), term(), map()) -> map(). |
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upsert(Key, Value, Map) -> |
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upsert_(Key, Value, {value, Map}, [], []). |
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upsert_([], Value, _, [], []) -> |
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Value; |
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upsert_([], Value, _, [{value, Map}|Maps], [Key|Keys]) -> |
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upsert_([], Map#{Key=>Value}, none, Maps, Keys); |
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upsert_([], Value, _, [none|Maps], [Key|Keys]) -> |
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upsert_([], #{Key=>Value}, none, Maps, Keys); |
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upsert_([H|T], Value, none, Maps, Keys) -> |
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upsert_(T, Value, none, [none|Maps], [H|Keys]); |
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upsert_([H|T], Value, {value, Map}, Maps, Keys) -> |
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Elem = lookup([H], Map), |
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upsert_(T, Value, Elem, [{value, Map}|Maps], [H|Keys]). |
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%% @doc |
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%% Remove the element at *Path* inside *Map*. Returns Map unchanged when the |
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%% path cannot be resolved. An empty path clears the map. |
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-spec remove(key(), map()) -> map(). |
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remove([], _Map) -> |
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#{}; |
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remove(Path, Map) -> |
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[KeyToDelete|PathToKeepRev] = lists:reverse(Path), |
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PathToKeep = lists:reverse(PathToKeepRev), |
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case lookup(PathToKeep, Map) of |
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{value, MapToDelete} when is_map(MapToDelete) -> |
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upsert(PathToKeep, maps:remove(KeyToDelete, MapToDelete), Map); |
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_ -> |
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Map |
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end. |
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%% @doc |
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%% Remove entries whose value is none and unwrap {value, V}. |
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-spec filter(maps:map(Key, klsn:'maybe'(Value))) -> maps:map(Key, Value). |
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filter(Map) -> |
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maps:filtermap(fun |
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(_, {value, Value}) -> |
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{true, Value}; |
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(_, none) -> |
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false |
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end, Map). |
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%% @doc |
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%% Produce a new map where keys become values and vice-versa. |
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-spec invert(maps:map(Key, Value)) -> maps:map(Value, Key). |
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invert(Map) -> |
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maps:from_list(lists:map(fun({Key, Value})-> |
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{Value, Key} |
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end, maps:to_list(Map))). |