implement Constraint, Substitution

src/main/java/edu/kit/typicalc/model/Constraint.java

@@ -6,6 +6,10 @@ import edu.kit.typicalc.model.type.Type;
  * Constrains two types to be equal.
  */
 public class Constraint {
+
+    private final Type a;
+    private final Type b;
+
     /**
      * Creates a new constraint using the two types.
      *
@@ -13,23 +17,23 @@ public class Constraint {
      * @param b second type
      */
     public Constraint(Type a, Type b) {
-        // TODO
+        // TODO: null checks?
+        this.a = a;
+        this.b = b;
     }
 
     /**
      * @return the first type
      */
     public Type getFirstType() {
-        return null;
+        return a;
-        // TODO
     }
 
     /**
      * @return the second type
      */
     public Type getSecondType() {
-        return null;
+        return b;
-        // TODO
     }
 
 }

src/main/java/edu/kit/typicalc/model/Substitution.java

@@ -7,6 +7,10 @@ import edu.kit.typicalc.model.type.TypeVariable;
  * A substitution specifies that some type should be replaced by a different type.
  */
 public class Substitution {
+
+    private final TypeVariable a;
+    private final Type b;
+
     /**
      * Creates a new substitution using a type variable a and a type b. When the substitution is applied to a type,
      * all occurring instances of a should be substituted with b.
@@ -15,22 +19,22 @@ public class Substitution {
      * @param b type to insert
      */
     public Substitution(TypeVariable a, Type b) {
-        // TODO
+        // TODO: null checks?
+        this.a = a;
+        this.b = b;
     }
 
     /**
      * @return the type variable
      */
     public TypeVariable getVariable() {
-        return null;
+        return a;
-        // TODO
     }
 
     /**
      * @return the replacement type
      */
     Type getType() {
-        return null;
+        return b;
-        // TODO
     }
 }