Modification Prevention Prefix Final

1 Simple Example

A variable declared as final in a member modification cannot be further modified by another modification. All members of a final member are also final, e.g. the fields of a final member that is a record are final.

type Angle = Real(final quantity = "Angle", final unit = "rad", displayUnit = "deg");
class AngleInst parameter Angle a1(unit = "deg",fixed=true); // Error, since unit declared as final parameter Angle a2(displayUnit = "rad", fixed=true); // Fine end AngleInst;

2 Simulation of Angle

When we simulate the class AngleInst we see that there is an error, since we try to modify the unit which is declared as final. We also get a warning because a1 and a2 do not have any default values.

simulate( AngleInst ) // 2015-09-08: OMC bug - allows to modify units declared as final

3 More Advanced Example

Here is another, slightly more advanced, example of the use of final. This example invovles a model that is used as a transfer function within a PI controller.

block TransferBlock // Works like a transfer function parameter Real a[:] = {1, 1} "denominator coefficient vector"; parameter Real b[:] = {1} "numerator coefficient vector"; protected parameter Integer nb(max = na) = size(b, 1); parameter Integer na = size(a, 1); parameter Integer n = na - 1; parameter Real[n] x "State vector"; parameter Real[na] b0 = cat(1, zeros(na - nb), b); end TransferBlock;
model PI "PI controller" parameter Real k = 1 "gain"; parameter Real T = 1 "time constant"; TransferBlock tf(final a = {T, 0}, final b = {T, 1}); end PI;
model Test PI c1(k = 2, T = 3); // Fine PI c2(tf.b = {1}); // Error: b is declared as final end Test;
model Test2 PI c1(k = 2, T = 3); // Fine end Test2;

4 Instantiation of PI

instantiateModel( TransferBlock )
instantiateModel( PI )
instantiateModel( Test ) // 2015-09-08: OMC bug - allows to modify final parameters

We see in the instantiaten of Test that an error occurs because we try to modify b, which is declared as final.

instantiateModel( Test2 )