5.7. Complex Mappings

You can have mappings of mappings. For example:

  mapping numbers = ([
                       "roman": ([
                                   "i": 1,
                                   "iv": 4,
                                   "v": 5
                                ]),
                       "english": ([
                                     "1": 1,
                                     "4": 4,
                                     "5": 5
                                  ])
                    ]);

  numbers["roman"]["i"];      // this is 1
  numbers["english"]["1"];    // this is also 1

Mappings can also be composed using the '*' operator (composed in the mathematical sense of the word):

  mapping m1 = ([ ]), m2 = ([ ]), m3;

  m1["a"] = "b";
  m2["b"] = "c";

  m3 = m1 * m2 

  //
  // m3 = "a" -> "c"
  //

You may also add two mappings. The sum of two mappings is defined as the union of the two mappings.

  mapping m1 = ([ ]), m2 = ([ ]), m3;

  m1["a"] = "b";
  m2["b"] = "c";

  m3 = m1 + m2;

  //
  // m3 = "a" -> "b"
  //      "b" -> "c"
  // 

The subtraction operator is not defined for mappings (use map_delete()).