Operator Overloading

Except three operators ($, ||, &&), the rest operators can be overloaded.

Overloading depends on a group of hook functions, their naming convention is:

__<type>_<optype>_operator__

type includes:

• array
• bool
• func
• int
• nil
• obj
• real
• str

optype includes:

• assign =
• pluseq +=
• subeq -=
• lmoveqi <<=
• rmoveq >>=
• muleq *=
• diveq /=
• oreq |=
• andeq &=
• xoreq ^=
• modeq %=
• cor |
• cand &
• cxor ^
• equal ==
• nonequal !=
• lt <
• le <=
• gt >
• ge >=
• lmov <<
• rmov >>
• plus +
• sub -
• mul *
• div /
• mod %
• sdec -- e.g. i--
• sinc ++ e.g. i++
• index []
• property .
• negative -
• reverse ~
• not !
• pinc ++ e.g. ++i
• pdec -- e.g. --i

Example:

Sys = Import('sys');

@__int_cand_operator__(left, right)
{
    Sys.print(left);
    Sys.print(right);
    return true;
}
sys.print((1 & 2));

This example will overload int operator & . The output is:

1
2
true

Which means the expression value is the return value of __int_cand_operator__.

Let’s change something:

Sys = Import('sys');

@__int_cand_operator__(left, right)
{
    Sys.print(left);
    Sys.print(right);
    return left & right;
}
sys.print((1 & 2));

Now, the output is:

1
2
0

& in its hook functions will not be overloaded.

Operator overloading on object is a little bit different. Besides the way that shown above, the hook functions can be existed in Set definition.

Example:

Sys = Import('sys');

S {
  attr;
  @__obj_cand_operator__(&left, &right)
  {
      Sys.print(left);
      Sys.print(right);
      return true;
  }
}

a = $S;
b = $S;
Sys.print((a & b));

The output is:

OBJECT
OBJECT
true

In this example, hook function __obj_cand_operator__ is given in a Set definition.

Another Example:

Sys = Import('sys');

S {
  attr;
  @__obj_cand_operator__(&left, &right)
  {
      Sys.print(left);
      Sys.print(right);
      return true;
  }
}

@__obj_cand_operator__(left, right)
{
    Sys.print(left);
    Sys.print(right);
    return false;
}
O {
  attr;
}

a = $S;
b = $S;
c = $O;
d = $O;
Sys.print((a & b));
Sys.print((c & d));

The output is:

OBJECT
OBJECT
true
OBJECT
OBJECT
false

In this example, & between the objects of Set S will call the hook function defined in S, and Set O objects will triggered global function __obj_cand_operator__.