is, as, Casting

• is (type query)
  • See Cpp2 is:
    • obj is Int (i.e. a type)
    • objPtr is T* instead of dynamic_cast<T*>(objPtr) != NullPtr
    • obj is cilia::Array (i.e. a template)
    • obj is cilia::Integer (i.e. a concept)
  • TODO Also support value query?
• as
  • See Cpp2 as
    • obj as T instead of T(obj)
    • objPtr as T* instead of dynamic_cast<T*>(objPtr)
    • With Variant v where T is one alternative:
      v as T instead ofstd::get<T>(v)
    • With Any a:
      a as T instead of std::any_cast<T>(a)
    • With Optional<T> o:
      o as T instead of o.value()
• Constructor casting
  • Float(3)
  • Casting via constructor is explicit by default, implicit as option.
  • No classic C-style casting: (Float) 3
  • but also
    • castToMutable<T>(...) or mutableCastTo<T>(...)
      • instead of constCastTo<>(...)
    • reinterpretCastTo<T>(...)
    • staticCastTo<T>(...)?
• Automatic casts
  • as in Kotlin,
  • for template types, references and pointers.

  • func getStringLength(Type obj) -> Int {
        if obj is String {
            // "obj" is automatically cast to "String" in this branch
            return obj.length
         }
        // "obj" is still a "Type" outside of the type-checked branch
        return 0
    }
    

  • func getStringLength(Type obj) -> Int {
        if not obj is String
            return 0
        // "obj" is automatically cast to "String" in this branch
        return obj.length
    }
    

  • func getStringLength(Type obj) -> Int {
        // "obj" is automatically cast to "String" on the right-hand side of "and"
        if obj is String  and  obj.length > 0 {
            return obj.length
        }
        return 0
    }
    

  • TODO Multiple inheritance is problematic here:
    • In Cilia/C++, an object can be an instance of several base classes at once, whereby the pointer (sometimes) changes during casting.
    • What if you still want/need to access the functions for a Type obj after if obj is ParentA?
      • Workaround:
        • In case of multiple inheritance there is no automatic casting.
        • Cast back with Type(obj).functionOfA()