new tasks

Task/Arrays/Erlang/arrays.erl

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+  %% Create a fixed-size array with entries 0-9 set to 'undefined'
+  A0 = array:new(10).
+  10 = array:size(A0).
+
+  %% Create an extendible array and set entry 17 to 'true',
+  %% causing the array to grow automatically
+  A1 = array:set(17, true, array:new()).
+  18 = array:size(A1).
+
+  %% Read back a stored value
+  true = array:get(17, A1).
+
+  %% Accessing an unset entry returns the default value
+  undefined = array:get(3, A1).
+
+  %% Accessing an entry beyond the last set entry also returns the
+  %% default value, if the array does not have fixed size
+  undefined = array:get(18, A1).
+
+  %% "sparse" functions ignore default-valued entries
+  A2 = array:set(4, false, A1).
+  [{4, false}, {17, true}] = array:sparse_to_orddict(A2).
+
+  %% An extendible array can be made fixed-size later
+  A3 = array:fix(A2).
+
+  %% A fixed-size array does not grow automatically and does not
+  %% allow accesses beyond the last set entry
+  {'EXIT',{badarg,_}} = (catch array:set(18, true, A3)).
+  {'EXIT',{badarg,_}} = (catch array:get(18, A3)).