Data Types

Strings

• What are the different ways Strings can be implemented in programming languages?
  • Array of char (i.e., nothing too special)
  • Fundamental, built-in data type
  • Just another class
  • A very special class.
• Example language for each type?
• What are the relative advantages and disadvantages of each?
  • Making the string class special means things like = just work.
  • Similarly, string ops can be done using built-in operators (e.g., +) instead of more verbose method calls
• 2nd key question: Should strings have static or dynamic length
  • Java strings are immutable. Can’t modify them, you have to get a new one

Enumerations

• What’s bad about just using constants?
  • (e.g., check_for_win(....., 1))
• Why not just set up const int HORIZONTAL = 1?
  • It solves some problems, but allows others (like setting month to 100)
• Enums are often just integers “under the hood”. With that in mind, do you
  • Allow assignments like DayOfWeek dueDate = 4 (if there are at lest 4 valid values)
  • Allow dueDate += 1?
  • Allow users to choose the underlying integers? (enum colors {red = 1, blue = 1000, green = 100000})
• What are the main language criteria affected by the design and use of enums?
  • Readability, reliability.
• Java Enums are interesting because they are an enumerated list of class instances. Thus, they are objects and can have methods and instance data https://docs.oracle.com/javase/tutorial/java/javaOO/enum.html

Strong Typing

• Note: The concept of strong typing is not formal, and not everybody agrees on what exactly it means.
• A language is strongly typed if “type errors are always detected” (either at compile-time or run time).
  • (Notice that this is not the same as statically typed.)
  • Is C strongly typed? Why/why not? (Give examples.)
  • Is C++ strongly typed? Why/why not? (Give examples.)
  • Is Java strongly typed? * Mostly. Consider float x = y + z where y is a float and z is an int. This is almost always what the programmer wants; but, it could be an error in rare cases.
  • Is JavaScript strongly typed?
    • No. It will do all kinds of type conversions automatically: 10 + "some string"
• In general coercion reduces reliability because it reduces the number and types of mistakes that can be automatically detected. Consider the following:

   int a;
   int b
   double c;
   double d;

   c = a + b

Suppose the programmer meant to type a + d. A language without coercion would catch the error.