On Tue, 04 Mar 2014 13:30:04 +0000, BartC wrote: > "Steven D'Aprano" <st...@pearwood.info> wrote in message > news:53159540$0$2923$c3e8da3$76491...@news.astraweb.com... > >> It's that "explicitly" part that doesn't follow. Having to manage types >> is the most tedious, boring, annoying, *unproductive* part of languages >> like Java, C and Pascal. Almost always, you're telling the compiler >> stuff that it can work out for itself. > > Isn't creating classes in Python similar to creating types elsewhere?
Depends on the type: I suppose you can draw an analogy between records or structs and classes with no methods. But I'm not talking about creating types, I'm talking about type declarations. int x=2; # 2 is an int? Who would have guessed! >> In the same way that managing jumps for GOTO has been automated with >> for loops, while, etc., and managing memory has been automated, there's >> no good reason not to allow the compiler to manage types. Dynamically >> typed languages like Python do so at runtime. Type inference simply >> allows statically typed languages to do the same only at compile time. > > Eliminating 'goto' is simple code-generation logic; type inference is > more of an art. Type inference is nothing like an art. It's a mathematically provable correct algorithm from the lambda calculus. http://en.wikipedia.org/wiki/Hindley%E2%80%93Milner Unfortunately the wikipedia page above appears to be complete gobbledygook if you aren't an expert in the lambda calculus, which I certainly am not, so I'm not even going to try to explain how it works. But there is no *guessing* involved, no heuristics which only sometimes work. There are certain assumptions involved, e.g. that the type of something is, in the absence of a declaration otherwise, the *most* general thing it could be (e.g. "it's an integer" rather than "it's an integer between 3 and 27"). But they're reasonable, practical assumptions. > But declaring variables is not just about specifying a type; it > registers the name too so that misspelled names can be picked up very > early rather than at runtime (and that's if you're lucky). You don't need to have static typing to have declared variables. The two are independent. E.g. one might have a system like Python, except you have to declare your variables before using them: global x local a a = x+1 ... Or a system like (ancient) BASIC, where the type of the variable is given by the name. E.g. X is a numeric variable, and X$ is a string variable. There's no need for a separate declaration, because the presence or absence of the $ sign tells the interpreter whether it is a number or string variable. Perl, PHP and many other languages also use sigils. Having to declare variables, and having to declare their type, are independent. -- Steven D'Aprano http://import-that.dreamwidth.org/ -- https://mail.python.org/mailman/listinfo/python-list
