src/kjs/DESIGN.ideas

0001 Get rid of SourceElementsNode by integrating its functionality into
0002 StatementNode.
0003
0004 ==========================================================================
0005
0006 The hash value of a string could be calculated at creation time and be
0007 stored in the UString instance for later use by the lookup functions.
0008
0009 ==========================================================================
0010
0011 Proposal for a new object model. Far from being complete.
0012
0013   Object                            Type
0014 +---------+                    +-------------+
0015 |  type   | ---------------->  | toString()  |
0016 |         |                    | toNumber()  |
0017 |  data   |                    |   ....      |
0018 +---------+                    | construct() |
0019      |                         +-------------+
0020      |                                |   /|\
0021     \|/                               |    |
0022 +---------+                           |    |
0023 |  type   |                           |    |
0024 |         | Shared (optional)        \|/   |
0025 |  data   |                       +-------------+
0026 +---------+     +---------+       | types       |
0027        /|\      |         |<------| gc          | Interpreter/Environment
0028         +-------|         |       |   ....      |
0029                 |         |       | excp state  |
0030                 +---------+       +-------------+
0031               Garbage Collector
0032
0033 Features:
0034         - offers class static data (nice replacement for pointers to member
0035         function objects in the prototype object)
0036         - no more need to pass around ExecState pointers for the C++ user
0037         (substituted with the need for Object* in the type implementation)
0038         - simple types are stored simple (no new'ed Imp objects)
0039
0040 Alternative A: pass around Object by pointer rather than value
0041                rather than new'ing they should come out of a pool
0042
0043 Alternative B: instead of virtual functions like toBoolean(), Type could
0044                have an array of function pointers which can be modified
0045                on the fly and checked for != 0.
0046
0047 Limitations: Konqueror's requirement to allow access to other frame's
0048              interpreter data but flagging errors on the caller's side
0049              is not satisfied.
0050
0051 class Interpreter;
0052
0053 class Type {
0054 public:
0055   Type(Interpreter* i, Type *b) : ip(i), bs(b) { }
0056   virtual UString name() const = 0;
0057   Type* base() const { return bs; }
0058   Interpreter* interpreter() const { return ip; }
0059
0060   virtual bool toBoolean(Object *o);
0061   // ....
0062   virtual Object construct(const List &args);
0063
0064   // factory
0065   Boolean newBoolean(bool b) { return Boolean(interpreter(), b); }
0066
0067 private:
0068   Interpreter* ip;
0069   Type* bs;
0070 };
0071
0072 union Data {
0073    bool b;
0074    double d;
0075    // UString ???
0076    Shared* sh;
0077 };
0078
0079 class Object {
0080 public:
0081    // creation
0082    Boolean newBoolean(bool b) { return Boolean(typ->interpreter(), b); }
0083
0084    // conversion
0085    bool to Boolean() const { return typ->toBoolean(this); }
0086
0087    // this object's "parent"
0088    Interpreter* interpreter() const { return typ->ip; }
0089 private:
0090    Type* typ;
0091    Data dat;
0092 };
0093
0094 class Boolean : public Object {
0095 public:
0096    // used by convenience function newBoolean()
0097    Boolean(Interpreter *i, bool b) {
0098       typ = i->booleanType();
0099       dat.b = b;
0100    }
0101    Boolean(const Boolean &b) {
0102       typ = b.typ;
0103       dat.b = b.b;
0104    }
0105    Boolean& operator=(const Boolean &b) {
0106       type = b.typ;
0107       dat.b = b.b;
0108       return *this;
0109    }
0110 };