display, functions and operators overloading capabilities

Description

In Scilab, variable display, functions and operators may be defined for new objects using functions (Scilab coded or primitives).

Display

The display of new objects defined by tlist structure may be overloaded (the default display is similar to list's one). The overloading function must have no output argument and a single input argument. It's name is formed as follow %<tlist_type>_p where %<tlist_type> stands for the first entry of the tlist type component truncated to the first 9 characters.

Operators

Each operator which is not defined for given operands type may be defined. The overloading function must have a single output argument and one or two inputs according to the number of operands. The function name is formed as follow:

for binary operators: %<first_operand_type>_<op_code>_<second_operand_type>;

for unary operators: %<operand_type>_<op_code>;

extraction and insertion operators which are n-nary operators are described below.

Be careful, only the types registered by the typename function can be used in an overloading macros.

<operand_type>, <first_operand_type>, <second_operand_type> are sequence of characters associated with each data type as described in the following table:

<op_code> is a single character associated with each operator as described in the following table:

The overloading function for extraction syntax b= a(i1, ..., in) has the following syntax: b = %<type_of_a>_e(i1, ..., in, a)

and the syntax [x1, .., xm] = a(i1, ..., in) has the following syntax: [x1, .., xm] = %<type_of_a>_e(i1, ..., in, a) .

The overloading function associated to the insertion syntax a(i1, ..., in) = b has the following syntax: a = %<type_of_b>_i_<type_of_a>(i1, ..., in, b, a) .

The 6 char code may be used for some complex insertion algorithm like x.b(2) = 33 where b field is not defined in the structure x. The insertion is automatically decomposed into temp = x.b; temp(2) = 33; x.b = temp. The 6 char code is used for the first step of this algorithm. The 6 overloading function is very similar to the e's one.

Functions :

Some basic primitive function may also be overloaded for new data type. When such function is undefined for a particular data types the function %<type_of_an_argument>_<function_name> is called. User may add in this called function the definition associated with the input data types.

            var = tlist('tab', ['a', 'b'], ['x'; 'y'], rand(2, 2)) 

            typeof(var)

            function []=%tab_p(l)
            disp([[' '; l(3)] [l(2); string(l(4))]])
            endfunction

            var 

            's' + 1 

            function x=%c_a_s(a, b)
            x = a + string(b);
            endfunction

            's' + 1 

            sin('2 * x') 

            function x=%c_sin(a)
            x = 'sin(' + a + ')'
            endfunction

            sin('2 * x') 

See also

• tlist — Scilab object and typed list definition.
• disp — displays variables
• symbols — scilab operator names
• typeof — explicit type or overloading code of an object
• type — returns the type of a Scilab object
• typename — associates a name to variable type

History