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By Root 693 0

legal C++ statements. Instead of reporting an error, C++ will happily go on stomping through memory. Languages with very weak typing simply do not capture typing errors, so the behavior of certain operations is undefined. Weaker typing is sometimes convenient, and less predictable. As you've seen, typing is not always black and white. It's also a highly contentious issue among language experts. Strong versus weak typing is on a continuum. Some strongly typed languages like Java allow loopholes by letting the user cast objects to another type. Languages with the strongest possible typing allow no loopholes. Weaker typing allows, and may even require, coercions. The weakest possible typing doesn't do type checking at all at compile time or runtime, like Assembly language, for example.

Static Versus Dynamic Typing

The more interesting question by far is when typing is enforced. Static typing binds a type to an object, and language constructs like variables and parameters. Dynamic typing binds a type to an object at runtime. Dynamic typing doesn't say anything about a variable's container, or anything that a variable passes through. The type is bound to the object. Therefore, the type of containers can change. An imperfect rule of thumb is that static languages force you to declare variables, but dynamic languages don't.

Ironically, most dynamic languages also tend to be strongly typed. Most weakly typed languages tend to be static. Said another way, strong typing can be dynamic or weak, but weak typing is usually also static. You don't find many weakly and dynamically typed languages, beyond Assembly language. Figure 4-1 places programming languages on two axes. Java has strong, static typing. You know this, because you get type mismatch errors when you make certain kinds of mistakes. Compiling this:

class TypeTest {

public static void main(String args[ ]) {

i = 4; // Nope!!! Static typing

int j;

j = 4.2; // Nyet!!! Strong typing

}

}

...gives you this result:

TypeTest.java:3: cannot resolve symbol

symbol : variable i

location: class TypeTest

i = 4;

TypeTest.java:5: possible loss of precision

found : double

required: int

j = 4.2;

Figure 4-1. Java is a strongly and statically typed language

Sometimes, that's good. After all, a bug that gets caught at compile time takes much less time than a bug that gets solved much later. In general, though, the dynamic programmers that I interviewed said static typing simply mauls productivity.

Syntax

Initially, you immediately can see that Java's syntax forces you to do more work. You have to declare and type all of your variables and parameters. You also need to cast objects that are compatible but different, and convert objects that aren't. The extra syntax provides value—the compiler has more information to catch bugs earlier. There's a cost, too. Static typing makes you work harder to enter equivalent code to dynamically typed languages, but you also have more lines of code to understand, maintain, or enhance. It's very difficult to prove or disprove the notion that static typing makes you more or less productive in terms of hours at the keyboard, but you can show that static typing leads to more characters, and more code to read and maintain.

Raw code count is not definitive; if it were, Perl, with all of the two- or three-character shortcuts, would be the most productive language of all time. Still, it's suggestive. Java's syntax wouldn't be such a problem if you could limit the extra code to a few lines of code at the top or bottom of a program, but you can't. You need to declare types for parameters. You need a cast every time you take something out of a collection. This syntax only gets more invasive with generics.

Thought Process

Some of the costs related to typing are hidden costs . I believe that one such cost is related to high-level, conceptual work versus finishing work. It's usually preferable to do conceptual work first and finishing work later, because much of your code will be thrown away, especially at early stages.