yes sorry i meant global variables , the ones you define in workspace like a := 1.
On Sat, Dec 14, 2013 at 4:30 PM, Norbert Hartl <[email protected]> wrote: > > Am 14.12.2013 um 12:09 schrieb kilon alios <[email protected]>: > > why we need globals anyway ? why not use classes instead ? > > > Class names are globals. A class is registered in a global namespace by > its name. Names need to be looked up. How should it work in another way? > > Norbert > > The only use I see of globals is in workspace and I am sure we could find > a way to automate or make the creation of classes faster inside workspace > instead of using globals. Since OO is the very foundation of Pharo I don't > see why one would need globals anyway. If that forces us to make object > more flexible so be it. Way better than creating concepts that works with > this tools and not work with the other tool or could work if you do this > and that , ending up making things more complex than they need to be. > > I think it would make even the transition from workspace to browser > easier, or even completely replace workspace with the browser. > > I always found workspace unnecessary anyway. > > > On Sat, Dec 14, 2013 at 12:47 PM, Norbert Hartl <[email protected]>wrote: > >> >> >> > Am 14.12.2013 um 05:41 schrieb Igor Stasenko <[email protected]>: >> > >> > >> > As you may know, smalltalk global dictionary contain all symbols >> defined globally, >> > so you can access them directly in any piece of code i.e. when you >> write: >> > >> > Object new >> > >> > it actually means 'send message #new to object, associated with #Object >> name in globals dictionary. >> > >> > Most of globals are classes, but some of them , like Transcript, World, >> Display etc are not. >> > And i was always thinking there's something wrong with these globals >> (actually there's multiple 'wrongs'), but finally, i think i can answer >> myself, what is most basic wrong with them: they miss any form of >> declaration. >> > >> > Most of variables in smalltalk require declaration, such as temps, >> method arguments, instance variables , class variables, pool variables, >> > but not globals. >> > Even classes, from formal point of view do not require declaration, >> > because actually the usual: >> > >> > Object subclass: #Collection >> > instanceVariableNames: '' >> > classVariableNames: 'MutexForPicking RandomForPicking' >> > poolDictionaries: '' >> > category: 'Collections-Abstract' >> > >> > is _definition_ but not declaration: >> > >> > Collection definition => >> > >> > 'Object subclass: #Collection >> > instanceVariableNames: '''' >> > classVariableNames: ''MutexForPicking RandomForPicking'' >> > poolDictionaries: '''' >> > category: ''Collections-Abstract''' >> > >> > in fact, it is just a message sent to 'Object' variable (at some moment >> in the past) , and there's nothing >> > in language which enforces the rule that evaluating such expression >> must declare new global, named Collection, except from environment we're >> working in. >> > >> > The absence of declaration for globals leads to following problems: >> > since declaration point is not defined, all tools (including compiler) >> assume that given name always been there, and always accessible. Which >> leads to bootstrap problems. >> > There's no way to determine if given piece of code (which uses some >> global) will keep functioning properly, once you unload certain package. No >> way to determine dependencies (and as consequence the order of code loading >> during bootstrapping). >> > Also, it is hard to determine, to which package certain global belongs. >> While it is easy to tell for classes since they having category, for >> globals like Transcript, Display etc, there's no way to tell anything. >> > Piece of cake, you can say: since Display is instance of DisplayScreen >> class, then such variable must belong to same package as DisplayScreen, >> right? >> > Wrong! >> > Just for example, imagine i create variable named >> MyWindowMousePosition, which will contain an instance of Point. Does it >> means that such variable should belong to same package as Point class? I >> guess not. >> > >> > So, to sum up, i think we should really think how to introduce a way to >> declare globals in package-based ecosystem, where each global belongs to >> certain package, and then since packages form dependency hierarchy, you can >> easily detect whether you allowed to use certain global in given context or >> not, >> > to prevent forming dependency loops. >> > But even if we will weaken contract and allow having dependency loops, >> even in such case declarations can help us to clearly tell which pieces of >> code will stop functioning properly, if package which declares given >> variable are not present in system. >> > >> > The last aspect of bootstrapping problem is order of initialization, >> > because declaring variable doesn't means you can use it right away, >> > since it may be not properly initialized yet (otherwise we will be >> forced to always use lazy initialization pattern). >> > >> > From this perspective, IMO package should not only have unordered list >> of classes/symbols it declares/defines, but also contain information in >> which order they must be initialized while loaded. >> > From other side, i don't really like introducing too much formalism and >> rules, and keep them as minimal as possible, following smalltalk spirit. >> > >> > What you think? >> >> I think packages should be first class citizens. A package once loaded >> provides an environment/namespace/... that declares all the (exported) >> symbols that should be accesible global. The smalltalk dictionary should >> rather be a list of those namespaces/environments/... A package should also >> have an initialize method where you could specify order of class >> initialization if necessary ( and other things). Furthermore I would like >> to see class initializers idempotent. So when loading a package the package >> initialize is invoked first and then the class initializers, As they are >> idempotent a possible double invocation is not a problem. >> Dependencies are always hard. I would start thinking about metacello >> defining all the possible dependencies regarding platforms, platform >> versions etc. At load time there is only one dependency graph and that >> could be reflected by the system. And this graph is not dependent on the >> tool that loaded the code. >> With this in place unloading should be rather easy. Dependencies can warn >> the user about an harmful action and when the namespace is removed all >> global definitions are automaticall removed. >> >> That is what I think. But I also think that there should be a possibility >> to load something that doesn't end being global. A way to load a package >> that isn't added to the global namespace (smalltalk dictionary) but to a >> package namespace would also be very good. Not everything needs to global >> but we can only load global things. That is a flaw in my opinion. And it >> prevents cool things like loading multiple versions of a code in separate >> packages. >> >> Norbert >> > > >
