Classes and objects IV
Lecture 16

Review
Semantic rules
Implementing the semantic rules
Project

Review

Questions about the last class?

Quiz

What is the difference between virtual and non-virtual functions?

Quiz Discussion

Semantic rules

cd      ::=  class c { d* }            // class declaration

cd      ::=  impl c { f*  }            // class implementation

t       ::= int                        // integer type
          | bool                       // boolean type
          | string                     // string type
          | (t+) -> t                  // function type
          | class c                    // class type

n       ::= x                          // simple name
          | n . x                      // qualified name

s       ::= init x ;
          | delete x ;


// denotational semantics

[[ class c { d* } ]]  ::= struct c { [[ d* ]](c) };
[[ impl c { f+ } ]]   ::= [[ f+ ]](c)
[[ init x ; ]]        ::= x = malloc(sizeof(* x)); [[ initFuncs(x) ]]
[[ delete x ; ]]      ::= free(x);

[[ d ]](c)  ::= type.getFieldType(d.ID, c) ;
[[ f ]](c)  ::= f.returnType.getDeclarationType(mangleDefName(c, f.IO)) ( struct c * this [[ arg* ]] ) { [[ d* ]] [[ st* ]] }
[[ arg ]]   ::= , scope.getSymbol(arg.ID).getReferenceType(arg.ID)

Initializing function pointers

initFuncs(x) {
  type = scope.getTypeAnyScope(x)
  className = type.name
  classScope = scope.getScopeAny(className)
  for each symbol in classScope
    if classScope.symbols.get(symbol).key() == Type.Kind.FUNCTION
      emit( x -> symbol = mangleDefName(className, symbol) ; )
  scope.getScopeAny().symbols.keySet()
}

COOL is another illustration of the semantics of an object-oriented language.

Implementing the semantic rules

Project

(3.5 weeks)

Implement the ClassC extension to SimpleC, i.e., the type-checker extension and the code generation extension.

Skeleton
- Includes complete type checker and code generator
- ClassTypechecker.java
- ClassCodeGen.java

Getting the skeleton

Be sure to unzip the tarfile in the root of your existing repo. It depends on having access to the original Grammar.g4.

# from the parent of your project folder
wget http://www.cs.ucf.edu/~gazzillo/teaching/cop5621spring23/lectures/src/classc.tar
cd project-NAME
tar -xvf ../classc.tar ./
git add src/classc
git commit -m "Added classc skeleton"

References to keep on hand

Keep open the following while implementing the type checker
1. The ClassC grammar extension (Grammar.g4)
2. The type rules
3. The semantics

Classes and objects IV Lecture 16

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