Anders Heljsberg doesn't grok Python

While Debian was releasing Sarge and Steve Jobs was introducing MacX86 yesterday, Anders Hejlsberg spoke on C# at Microsoft Tech-Ed. James Avery writes:

After a couple questions from other people I was able to get in the other question I was dying to ask. What does Anders think about the resurgence in dynamic typing from languages like Python. Basically he said that he understands what benefits people are getting from dynamic typing, but he thinks they can get the benefits of dynamic typing without sacrificing strong typing. He talked about inferring type (what anonymous methods do now with delegates) and how that might be a way to get the coding speed and ease without sacrificing the strongly typed information.

Unfortunately, omitting type declarations is only a small part of Python-esque dynamism. One of the smallest, in fact. Far more important are the ability to modify objects and classes at runtime, which allow you to do things in Python that would require code generation (which is fragile, at best) or AOP language modifications to do in C# or Java.

Equally important is the attitude this fosters in the Python community: "Python assumes we're all consenting adults." "Private" restrictions are discouraged (and can still be bypassed by others if they're willing to do less work than performing ordinary refleciton requires in other languages.) As Sion Arrowsmith recently put it,:

Years of writing and maintaining others' C++ and Java code (plus one year of maintaining Python code and rather more writing) has led me to believe that there is no justification for truly private variables... [D]enying derived classes full access to your inner workings just leads to clumsier (less readable and more bug-prone) implementations derivations... [I]t's based on the hubris that you are a better programmer than anyone who might want to extend your class and can forsee all circumstances in which it might be subclassed.

This attitude of "we know better than you what code you will want to write" is found in the Java world, but it's really pervasive at Microsoft. C# methods are "final" by default; no polymorphism for you unless the original author was generous enough to specify "virtual!" This can be done in Java, but at least it's not the default. Also, huge parts of the runtime (in both .NET and Java, but more so in .NET) are "sealed," preventing subclassing entirely.

You couldn't inflict that on your users in a language like Python. Even if you could "seal" a Python class, which will never happen since it's a horrible misfeature, a user could still create his own class with the right attributes and nobody would know the difference (because of duck typing, another important part of the we're-adults-here philosophy). Well, unless you littered your code with isinstance calls, but nobody would use code THAT poorly written... if you want to play in Microsoft's world, you don't have a choice.