Homework 4

src/cd/frontend/semantic/InheritanceChecker.java

@@ -0,0 +1,75 @@
+package cd.frontend.semantic;
+
+import cd.frontend.semantic.SemanticFailure.Cause;
+import cd.ir.Ast.ClassDecl;
+import cd.ir.Ast.MethodDecl;
+import cd.ir.AstVisitor;
+import cd.ir.Symbol.ClassSymbol;
+import cd.ir.Symbol.MethodSymbol;
+import cd.ir.Symbol.VariableSymbol;
+import cd.util.Pair;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class InheritanceChecker extends AstVisitor<Void, Void> {
+	
+	ClassSymbol classSym;
+
+	@Override
+	public Void classDecl(ClassDecl ast, Void arg) {
+		classSym = ast.sym;
+		
+		// check for cycles in the inheritance hierarchy:
+		Set<ClassSymbol> supers = new HashSet<ClassSymbol>();
+		ClassSymbol sc = classSym.superClass;
+		supers.add(classSym);
+		while (sc != null) {
+			if (supers.contains(sc))
+				throw new SemanticFailure(
+						Cause.CIRCULAR_INHERITANCE,
+						"Class %s has %s as a superclass twice", 
+						ast.name, sc.name);
+			supers.add(sc);
+			sc = sc.superClass;
+		}
+		
+		this.visitChildren(ast, null);
+		
+		return null;
+	}
+
+	@Override
+	public Void methodDecl(MethodDecl ast, Void arg) {
+		
+		// check that methods overridden from a parent class agree
+		// on number/type of parameters
+		MethodSymbol sym = ast.sym;
+		MethodSymbol superSym = classSym.superClass.getMethod(ast.name);
+		if (superSym != null) {
+			if (superSym.parameters.size() != sym.parameters.size())
+				throw new SemanticFailure(
+						Cause.INVALID_OVERRIDE,
+						"Overridden method %s has %d parameters, " +
+						"but original has %d",
+						ast.name, sym.parameters.size(),
+						superSym.parameters.size());
+			for (Pair<VariableSymbol> pair : Pair.zip(sym.parameters, superSym.parameters))
+				if (pair.a.type != pair.b.type)
+					throw new SemanticFailure(
+							Cause.INVALID_OVERRIDE,
+							"Method parameter %s has type %s, but " +
+							"corresponding base class parameter %s has type %s",
+							pair.a.name, pair.a.type, pair.b.name, pair.b.type);
+			if (superSym.returnType != sym.returnType)
+				throw new SemanticFailure(
+						Cause.INVALID_OVERRIDE,
+						"Overridden method %s has return type %s," +
+						"but its superclass has %s",
+						ast.name, sym.returnType, superSym.returnType);
+		}
+		
+		return null;
+	}		
+
+}