Constraining Type of Replaceable Elements

1 General Description

A declaration of a replaceable element of a class can represent either a variable (as comp1 in MicroCircuit) or a local class declaration (as type CompType = Resistor in GenMicroCircuit2). The extends keyword in the second form has nothing to do with inheritance, it is just a reuse of the keyword for a different purpose. It is however recommended to avoid modifiers in the constraining type (the expression after the extends keyword).

2 MicroCircuit

class MicroCircuit replaceable Resistor comp1; end MicroCircuit;

In the class TempMicroCircuit the instance comp1 is modified to have the type TempResistor instead of Resistor.

class TempMicroCircuit = MicroCircuit(redeclare TempResistor comp1);

A more generic circuit expressing the same thing as TempMicroCircuit.

class GenMicroCircuit replaceable type CompType = Resistor; replaceable CompType comp1; end GenMicroCircuit;

Type Error, Inductor is not subtype of Resistor. By extending CompType = Resistor with TwoPin the redeclaration can be successfully done.

class InductorMicroCircuit = GenMicroCircuit(redeclare type CompType = Inductor);

3 Electrical Units

type Voltage = Real(Unit = "V");
type Current = Real(Unit = "A");

4 Connectors

connector Pin Voltage v; flow Current i; end Pin;

5 Component TwoPin

partial class TwoPin "Superclass of elements with two electrical pins" Pin p, n; Voltage v; Current i; equation v = p.v - n.v; p.i + n.i = 0; i = p.i; end TwoPin;

6 Generic MicroCircuit

After changing the GenMicroCircuit class there is no problem to define a more specific circuit, e.g. using the component type Capacitor.

class GenMicroCircuit2 replaceable type CompType = Resistor extends TwoPin; // No inheritance! replaceable CompType comp1; end GenMicroCircuit2;
class CapacitorMicroCircuit = GenMicroCircuit2(redeclare type CompType = Capacitor);

The CapacitorMicroCircuit has no replaceable CompType declaration left since the original replaceable declaration was replaced. Therefore we need to perform a redeclaration with redeclare replaceable to be able to perform further modifications.

class GenCapacitorMicroCircuit = GenMicroCircuit2(redeclare replaceable type CompType = TempCapacitor);

The constraining type of a replaceable redeclaration must be a subtype of the constraining type of the declaration it redeclares. This condition is fulfilled for GenCapacitorMicroCircuit above, since the constraining type GenCapacitor is a subtype of TwoPin. Thus the modifier R = 20 in the definition of MicroCircuit3 is propagated to both the declaration and the constraining type, which is apparent in the class MicroCircuit3expanded.

class MicroCircuit2 replaceable TempResistor R1 extends Resistor; end MicroCircuit2;
class MicroCircuit3 = MicroCircuit2(R1 (R = 20));
class MicroCircuit3expanded replaceable TempResistor R1(R = 20) extends Resistor(R = 20); end MicroCircuit3expanded;

In an element redeclaration of a replaceable element the modifiers of the replaced constraining type are merged to both the new declaration and to the new constraining type. The modifier R=30 for the constraining type Resistor below is propagated to the new type TempResistor2 and the new constraining type Resistor2.

class MicroCircuit4 replaceable TempResistor R1 extends Resistor(R=30); end MicroCircuit4;
class MicroCircuit5 = MicroCircuit4(redeclare replaceable TempResistor2 R1 extends Resistor2);
class MicroCircuit5expanded replaceable TempResistor2 R1(R = 30) extends Restistor2(R=30); end MicroCircuit5expanded;