Can someone tell me what Strong typing and weak typing means and which one is better?

Question

Can someone tell me what Strong typing and weak typing means and which one is better?

Answer 1

This article is a great read: http://blogs.perl.org/users/ovid/2010/08/what-to-know-before-debating-type-systems.html Cleared up a lot of things for me when researching trying to answer a similar question, hope others find it useful too.

Strong and Weak Typing:

Probably the most common way type systems are classified is "strong" or "weak." This is unfortunate, since these words have nearly no meaning at all. It is, to a limited extent, possible to compare two languages with very similar type systems, and designate one as having the stronger of those two systems. Beyond that, the words mean nothing at all.

Static and Dynamic Types

This is very nearly the only common classification of type systems that has real meaning. As a matter of fact, it's significance is frequently under-estimated [...] Dynamic and static type systems are two completely different things, whose goals happen to partially overlap.

A static type system is a mechanism by which a compiler examines source code and assigns labels (called "types") to pieces of the syntax, and then uses them to infer something about the program's behavior. A dynamic type system is a mechanism by which a compiler generates code to keep track of the sort of data (coincidentally, also called its "type") used by the program. The use of the same word "type" in each of these two systems is, of course, not really entirely coincidental; yet it is best understood as having a sort of weak historical significance. Great confusion results from trying to find a world view in which "type" really means the same thing in both systems. It doesn't.

Explicit/Implicit Types:

When these terms are used, they refer to the extent to which a compiler will reason about the static types of parts of a program. All programming languages have some form of reasoning about types. Some have more than others. ML and Haskell have implicit types, in that no (or very few, depending on the language and extensions in use) type declarations are needed. Java and Ada have very explicit types, and one is constantly declaring the types of things. All of the above have (relatively, compared to C and C++, for example) strong static type systems.

Answer 2

That'll be the theory answers taken care of, but the practice side seems to have been neglected...

Strong-typing means that you can't use one type of variable where another is expected (or have restrictions to doing so). Weak-typing means you can mix different types. In PHP for example, you can mix numbers and strings and PHP won't complain because it is a weakly-typed language.

$message = "You are visitor number ".$count;

If it was strongly typed, you'd have to convert $count from an integer to a string, usually with either with casting:

$message = "you are visitor number ".(string)$count;

...or a function:

$message = "you are visitor number ".strval($count);

As for which is better, that's subjective. Advocates of strong-typing will tell you that it will help you to avoid some bugs and/or errors and help communicate the purpose of a variable etc. They'll also tell you that advocates of weak-typing will call strong-typing "unnecessary language fluff that is rendered pointless by common sense", or something similar. As a card-carrying member of the weak-typing group, I'd have to say that they've got my number... but I have theirs too, and I can put it in a string :)