/**
* Type-checks this method declaration. It first checks that if this method overrides a method of
* a superclass then the return type is a subtype of that of the overridden method. Then it builds
* a type-checker whose only variable in scope is {@code this} of type {@code clazz} and the
* parameters of the method, and where return instructions of type {@code returnType} are allowed.
* It then type-checks the body of the method in that type-checker. It finally checks that if this
* method does not return {@code void}, then every execution path ends with a {@code return}
* command.
*
* @param clazz the semantical type of the class where this method occurs
*/
@Override
protected void typeCheckAux(ClassType clazz) {
TypeChecker checker;
ClassType superclass;
MethodSignature overridden;
Type rt = returnType.typeCheck();
// we build a type-checker which signals errors for the source code
// of the class where this method is defined,
// whose only variables in scope is this of type
// clazz and the parameters of the method, and
// where return instructions of type returnType are allowed
checker = new TypeChecker(rt, clazz.getErrorMsg());
// the main method is the only <i>static</i> method, where there is no this variable
if (!getSignature().getName().equals("main")) checker = checker.putVar("this", clazz);
// we enrich the type-checker with the formal parameters
checker = getFormals() != null ? getFormals().typeCheck(checker) : checker;
TypeList pars = getFormals() != null ? getFormals().typeCheck() : null;
// we check if this method overrides a method of some superclass
superclass = clazz.getSuperclass();
if (superclass != null) {
overridden = superclass.methodLookup(name, pars);
if (overridden != null)
// it does override a method of a superclass. We check
// that its return type has been refined. We use the
// canBeAssignedToSpecial method so that
// void can be overridden into void
if (!rt.canBeAssignedToSpecial(overridden.getReturnType()))
error(
checker,
"illegal return type for overriding method \""
+ name
+ "\". Was "
+ overridden.getReturnType());
}
// we type-check the body of the method in the resulting type-checker
getBody().typeCheck(checker);
// we check that there is no dead-code in the body of the method
boolean stopping = getBody().checkForDeadcode();
// we check that if the method does not return void then
// every syntactical execution path in the method ends with
// a return command (continue and break are forbidden in this position)
if (rt != VoidType.INSTANCE && !stopping) error(checker, "missing return statement");
}
/**
* Generates the Java bytecode corresponding to this Kitten bytecode.
*
* @param classGen the Java class generator to be used for this generation
* @return the Java {@code checkcast intoType} bytecode for casts between reference types and a
* type conversion bytecode such as {@code i2f} for conversions between numercial types
*/
@Override
public InstructionList generateJavaBytecode(AbstractClassGenerator classGen) {
if (intoType instanceof ReferenceType)
// we use the instruction factory to simplify the addition of the type to the constant pool
return new InstructionList(
classGen
.getFactory()
.createCheckCast((org.apache.bcel.generic.ReferenceType) intoType.toBCEL()));
else if (fromType == IntType.INSTANCE && intoType == FloatType.INSTANCE)
return new InstructionList(new I2F());
else // it must be float into int
return new InstructionList(new F2I());
}
