-spec append(Key, Value, Dict1) -> Dict2 when Dict1 :: dict(Key, Value), Dict2 :: dict(Key, Value).

Appends a new Value to the current list of values associated with Key.

See also section Notes.

-spec append_list(Key, ValList, Dict1) -> Dict2
                     when Dict1 :: dict(Key, Value), Dict2 :: dict(Key, Value), ValList :: [Value].

Appends a list of values ValList to the current list of values associated with Key. An exception is generated if the initial value associated with Key is not a list of values.

See also section Notes.

-spec erase(Key, Dict1) -> Dict2 when Dict1 :: dict(Key, Value), Dict2 :: dict(Key, Value).

Erases all items with a given key from a dictionary.

-spec fetch(Key, Dict) -> Value when Dict :: dict(Key, Value).

Returns the value associated with Key in dictionary Dict. This function assumes that Key is present in dictionary Dict, and an exception is generated if Key is not in the dictionary.

See also section Notes.

-spec fetch_keys(Dict) -> Keys when Dict :: dict(Key, Value :: term()), Keys :: [Key].

Returns a list of all keys in dictionary Dict.

-spec filter(Pred, Dict1) -> Dict2
                when
                    Pred :: fun((Key, Value) -> boolean()),
                    Dict1 :: dict(Key, Value),
                    Dict2 :: dict(Key, Value).

Dict2 is a dictionary of all keys and values in Dict1 for which Pred(Key, Value) is true.

-spec find(Key, Dict) -> {ok, Value} | error when Dict :: dict(Key, Value).

Searches for a key in dictionary Dict. Returns {ok, Value}, where Value is the value associated with Key, or error if the key is not present in the dictionary.

See also section Notes.

-spec fold(Fun, Acc0, Dict) -> Acc1
              when
                  Fun :: fun((Key, Value, AccIn) -> AccOut),
                  Dict :: dict(Key, Value),
                  Acc0 :: Acc,
                  Acc1 :: Acc,
                  AccIn :: Acc,
                  AccOut :: Acc.

Calls Fun on successive keys and values of dictionary Dict together with an extra argument Acc (short for accumulator). Fun must return a new accumulator that is passed to the next call. Acc0 is returned if the dictionary is empty. The evaluation order is undefined.

-spec from_list(List) -> Dict when Dict :: dict(Key, Value), List :: [{Key, Value}].

Converts the Key-Value list List to dictionary Dict.

-spec is_empty(Dict) -> boolean() when Dict :: dict().

Returns true if dictionary Dict has no elements, otherwise false.

-spec is_key(Key, Dict) -> boolean() when Dict :: dict(Key, Value :: term()).

Tests if Key is contained in dictionary Dict.

-spec map(Fun, Dict1) -> Dict2
             when
                 Fun :: fun((Key, Value1) -> Value2),
                 Dict1 :: dict(Key, Value1),
                 Dict2 :: dict(Key, Value2).

Calls Fun on successive keys and values of dictionary Dict1 to return a new value for each key. The evaluation order is undefined.

-spec merge(Fun, Dict1, Dict2) -> Dict3
               when
                   Fun :: fun((Key, Value1, Value2) -> Value),
                   Dict1 :: dict(Key, Value1),
                   Dict2 :: dict(Key, Value2),
                   Dict3 :: dict(Key, Value).

Merges two dictionaries, Dict1 and Dict2, to create a new dictionary. All the Key-Value pairs from both dictionaries are included in the new dictionary. If a key occurs in both dictionaries, Fun is called with the key and both values to return a new value. merge can be defined as follows, but is faster:

merge(Fun, D1, D2) ->
    fold(fun (K, V1, D) ->
                 update(K, fun (V2) -> Fun(K, V1, V2) end, V1, D)
         end, D2, D1).

-spec new() -> dict().

Creates a new dictionary.

-spec size(Dict) -> non_neg_integer() when Dict :: dict().

Returns the number of elements in dictionary Dict.

-spec store(Key, Value, Dict1) -> Dict2 when Dict1 :: dict(Key, Value), Dict2 :: dict(Key, Value).

Stores a Key-Value pair in dictionary Dict2. If Key already exists in Dict1, the associated value is replaced by Value.

-spec take(Key, Dict) -> {Value, Dict1} | error
              when Dict :: dict(Key, Value), Dict1 :: dict(Key, Value), Key :: term(), Value :: term().

This function returns value from dictionary and a new dictionary without this value. Returns error if the key is not present in the dictionary.

-spec to_list(Dict) -> List when Dict :: dict(Key, Value), List :: [{Key, Value}].

Converts dictionary Dict to a list representation.

-spec update(Key, Fun, Dict1) -> Dict2
                when
                    Dict1 :: dict(Key, Value),
                    Dict2 :: dict(Key, Value),
                    Fun :: fun((Value1 :: Value) -> Value2 :: Value).

Updates a value in a dictionary by calling Fun on the value to get a new value. An exception is generated if Key is not present in the dictionary.

-spec update(Key, Fun, Initial, Dict1) -> Dict2
                when
                    Dict1 :: dict(Key, Value),
                    Dict2 :: dict(Key, Value),
                    Fun :: fun((Value1 :: Value) -> Value2 :: Value),
                    Initial :: Value.

Updates a value in a dictionary by calling Fun on the value to get a new value. If Key is not present in the dictionary, Initial is stored as the first value. For example, append/3 can be defined as:

append(Key, Val, D) ->
    update(Key, fun (Old) -> Old ++ [Val] end, [Val], D).

-spec update_counter(Key, Increment, Dict1) -> Dict2
                        when Dict1 :: dict(Key, Value), Dict2 :: dict(Key, Value), Increment :: number().

Adds Increment to the value associated with Key and stores this value. If Key is not present in the dictionary, Increment is stored as the first value.

This can be defined as follows, but is faster:

update_counter(Key, Incr, D) ->
    update(Key, fun (Old) -> Old + Incr end, Incr, D).