Objects

Objects

I've implemented objects in a simple - and inefficient way - a linked list of property descriptors. Previously it was a hash map, but generic hash map in C libraries are somewhat gnarly and didn't teach me anything about what I'm trying to learn: compilation and language implementation.

typedef struct JsObject {
    PropertyDescriptor* properties;
    PropertyDescriptor* tailProperty;

    // Internal slots - implementation visible only
    JsValue* prototype;

    // determines if this is callable - i.e [[Call]] internal slot
    FunctionRecord* callInternal;
} JsObject;

You can see the properties exposed in JS-land, e.g o.foo = 'bar', are distinct from the internal properties that are required to implement JS like prototype.

Strings

I have two types of strings: interned and heap. Interned strings are those where the value is found in the source of the JS program, e.g:

var obj = {
  foo: "bar",
}
var objName = "obj"
console.log(global[obj]);

Would intern "obj", "foo", "bar", and "objName". These are allocated at startup of the compiled program: