.. efun:: mixed deep_copy(mixed value)

  Create a deep copy of :arg:`value` and return it. For arrays and mappings this means that a new array or mapping is created with copies of the original content. Embedded arrays and mappings are truly copied, too.

  For other values this function is a no-op.

  If DYNAMIC_COST is defined, every nested mapping or array counts towards the evaluation cost in both size and nesting depth.

  .. usage::

    In contrast to the example in :efun:`copy`, changes to the nested array below are not visible in both copies::

      mixed *a, *b;

      a = ({ 1, ({ 21, 22 }) });
      b = deep_copy(a);
      a[0] = -1;
      a[1][0] = -21;

      // a is now   ({ -1, ({ -21, 22 }) })
      // b is still ({  1, ({  21, 22 }) })

  :history 3.2.6 introduced:
  :history 3.2.9 changed: added the dynamic cost to the efun

  .. seealso:: :efun:`copy`