October 2016 - Pharo-dev - lists.pharo.org

Re: [Pharo-dev] How does Pharo store instance variables?

by Ben Coman

On Tue, Oct 4, 2016 at 4:23 AM, CodeDmitry <dimamakhnin(a)gmail.com> wrote: > I am trying to study Pharo's internals and I am now curious how it stores > class variables. > > I notice that in order to have a class `Greeter` with a "static" variable > `greeting`, I guess you are referring to... http://www.learncpp.com/cpp-tutorial/811-static-member-variables/ So its fair to analogize to a familiar concept, but you need to remember... Rule 1: *Everything* is an object. which includes class definitions, being instances of Metaclass. So try... Metaclass allInstances inspect. then select one and compare its 'methodDict' and 'thisClass' ==> 'methodDict' with what you see for that class in the System Browser. Notice the ClassDescription superclass to Metaclass has an instance variable 'instanceVariables'. Now one thing that confused me for a moment just now is, if you try... Metaclass allInstances select: [ :mc | mc instanceVariables size > 0 ]. then look at that instance variable 'instanceVariables' it is always nil due to the implementation in Pharo 5 of instance variables as Slots. In Pharo 4 you see actual names of instance variables. btw I'm curious now, does that ivar 'instanceVariables' planned to be removed some time? Now actually (IIUC) a C++ static member variable is most like a "Class Variable" which is defined on the instance side of a class. There are three main variable types to consider when defining a class in Pharo: Instance variables - scoped to instance methods, unique per instance Class Variables - scoped to instance methods & class methods, common to the class and all subclasses and all their instances Class Instance Variables - scoped to class methods, unique per class (i.e. instance of Metaclass) To experience the finer points of these you might try the experiment I describe here... http://forum.world.st/Class-vars-and-inst-vars-of-a-class-tp4749910p4749914… > I need to make `greeting` an instance variable under "show > the class side" and create a "Getter" and "Setter" for this "instance > variable". > > First thing that confuses me is, why is this called an instance variable if > this particular "static" method is not bound to any particular instance? The method is bound to an instance of Metaclass, being the class definition. When you add methods or instance variables to the class-side in the Browser, you are adding them to this instance. There is one instance of Metaclass for each class in the system. > Is > it just because it is defined in an "instance" of a "ProtoClass"? I don't understand this question. Can you rephrase after doing the experiment linked above? > > Second thing that confuses me is, where are these pairs of ("instance > variable name" => "instance variable value") stored? I know that I can call > > Transcript show: > ((Greeter class) instanceVariables at: 1). > > which prints "greeting". > > and > > Transcript show: > Greeter instanceVariables class. > > which prints "Array"(curious, i expected a Dictionary mapping Strings to > Object). What you are seeing is a copy of the core representation. Try debugging into.... (Greeter class instanceVariables at: 1) paying particular attention to... LayoutClassScope>>visibleSlots LayoutClassScope>>do: > > Transcript show: > ((Greeter class) instanceVariables at: 1) class. > > prints "ByteSymbol". > > Now I am confused, where are the actual values of the "static variables" > stored? I can find the names, but can't understand where the values are > hidden. You are looking at a copy of the core representation. To work through a quick example... take the Morph class definition's first two instanceVariables: 'bounds owner...' and for each of their accessors #bounds and #owner right-click and choose <Inspect Method> then compare each [Bytecode] tab with the first line showing "callPrimitive: 264" or "callPrimitive: 265" respectively. These (and similar) primitives provide the *real* "compiled" access to the instance variables. So that demostration is the equivalent of asking "where are the values in variables stored" for C++ and reviewing its generated assembler code - although our VM provides a level of abstraction. Hopefully the ease of digging from source code down to its compiled bytecode demonstrates another aspect of the power of the Pharo environment. btw, you can see the list of VM primitives here... https://github.com/pharo-project/pharo-vm/blob/36079d9be14542ea9e0d72e5ef57… cheers -ben

Oct. 4, 2016

Re: [Pharo-dev] How does Pharo store instance variables?

by Martin McClure

On 10/03/2016 01:23 PM, CodeDmitry wrote: > I am trying to study Pharo's internals and I am now curious how it stores > class variables. > > I notice that in order to have a class `Greeter` with a "static" variable > `greeting`, I need to make `greeting` an instance variable under "show show > the class side" and create a "Getter" and "Setter" for this "instance > variable". > > First thing that confuses me is, why is this called an instance variable if > this particular "static" method is not bound to any particular instance? Is > it just because it is defined in an "instance" of a "ProtoClass"? > > Second thing that confuses me is, where are these pairs of ("instance > variable name" => "instance variable value") stored? I know that I can call > > Transcript show: > ((Greeter class) instanceVariables at: 1). > > which prints "greeting". > > and > > Transcript show: > Greeter instanceVariables class. > > which prints "Array"(curious, i expected a Dictionary mapping Strings to > Object). > > Transcript show: > ((Greeter class) instanceVariables at: 1) class. > > prints "ByteSymbol". > > Now I am confused, where are the actual values of the "static variables" > stored? I can find the names, but can't understand where the values are > hidden. > > Can somebody help me understand this? You've run into one of the core truths of Smalltalk. Both of the following two statements are true: 1) Every object is an instance of some class. 2) Every class is an object. --- So, every class must be the instance of some class. What is the class of a class? Every time you define a class, you are actually defining a pair of classes -- the class, and another class to be the class of that class. The latter is known as a "metaclass" and it is always an instance of Metaclass. Each Metaclass has exactly one instance, which is a class. The class defines "instance-side" behavior and variables, and the metaclass defines "class-side" behavior and variables. This lets the same rules apply for both normal classes and metaclasses. For instance, every instance of a class contains a variable for each variable defined in its class. So if you define a named instance variable on a normal class, every instance of that class will contain its own copy of that variable. If you define a named instance variable in a metaclass, every instance of that metaclass will have its own copy of that variable. But metaclasses only have one instance, the class, so there's only one copy of that variable. Until you subclass that class. The instance-side instance variables are inherited, and so are the class-side instance variables. So you get a new metaclass that's a subclass of the old metaclass, and a new class that's a subclass of the class. This new subclass is distinct from its superclass, so it gets its *own* copy of the class instance variable, just like any other object. This is one way in which class instance variables are different from static variables. They're not really static at all, but they do have the lifetime of the class, just like any instance variable has the lifetime of the object it's in. And the usual rules of access to instance variables apply, which is why you need getter/setter methods if you want to access the variable from outside that class object. I hope this helps you understand Smalltalk a bit better. There are also class variables, which Nicolas mentioned, and which are quite different, and which are closer to static variables. Regards, -Martin

Oct. 4, 2016

Re: [Pharo-dev] How does Pharo store instance variables?

by CodeDmitry

Oh! I see where I got confused now! "static" variables in Pharo outlive their Playground call! If I call Greeter greet. Greeter greeting: 'Hi!'. Greeter greet. Even if greet sets greeting to an initial value if it is nil, it will forever then stay 'Hi!' until I change it or reset it. So it is not unreasonable to get a response 'Hi! Hi!' in the playground even though 'Hi!' only gets set after greet is called, since the global state outlives the Transcript! -- View this message in context: http://forum.world.st/How-does-Pharo-store-instance-variables-tp4917924p491… Sent from the Pharo Smalltalk Developers mailing list archive at Nabble.com.

Oct. 4, 2016

Re: [Pharo-dev] How does Pharo store instance variables?

by Nicolas Passerini

If you defined the variable as an instance variable in the class side, you can access it as Greeter instVarNamed: 'greeting' or Greeter instVarAt: 1 But also you can define class variables from the instance side, which is slightly different (and I think most common, isn't it?) Object subclass: #Greeter instanceVariableNames: '' classVariableNames: 'greeting' package: 'Greetings' if that is the case, there is in fact a dictionary which is accessed by doing Greeting classPool On Mon, Oct 3, 2016 at 10:23 PM, CodeDmitry <dimamakhnin(a)gmail.com> wrote: > I am trying to study Pharo's internals and I am now curious how it stores > class variables. > > I notice that in order to have a class `Greeter` with a "static" variable > `greeting`, I need to make `greeting` an instance variable under "show show > the class side" and create a "Getter" and "Setter" for this "instance > variable". > > First thing that confuses me is, why is this called an instance variable if > this particular "static" method is not bound to any particular instance? Is > it just because it is defined in an "instance" of a "ProtoClass"? > > Second thing that confuses me is, where are these pairs of ("instance > variable name" => "instance variable value") stored? I know that I can call > > Transcript show: > ((Greeter class) instanceVariables at: 1). > > which prints "greeting". > > and > > Transcript show: > Greeter instanceVariables class. > > which prints "Array"(curious, i expected a Dictionary mapping Strings to > Object). > > Transcript show: > ((Greeter class) instanceVariables at: 1) class. > > prints "ByteSymbol". > > Now I am confused, where are the actual values of the "static variables" > stored? I can find the names, but can't understand where the values are > hidden. > > Can somebody help me understand this? > > > > > -- > View this message in context: http://forum.world.st/How- > does-Pharo-store-instance-variables-tp4917924.html > Sent from the Pharo Smalltalk Developers mailing list archive at > Nabble.com. > >

Oct. 3, 2016

Re: [Pharo-dev] New to Pharo; a bunch of questions.

by phil＠highoctane.be

Or just use the st command line handler to load your code. pharo-ui someimage.image st blah.st I do not know if it loads in Pharo5 but I had this working in Pharo3 that extends the File Browser in Pharo with additional buttons that allow you to edit external files easily. You can also steal this thing: https://github.com/vim-scripts/st.vim/blob/master/syntax/st.vim Useful for writing scripts indeed. Pharo can be used like Python, Perl, or Tcl for scripting from the command line. VTermOutputDriver is an interesting class to look at for that (does nice colors). Phil On Mon, Oct 3, 2016 at 10:40 PM, Richard Sargent < richard.sargent(a)gemtalksystems.com> wrote: > CodeDmitry wrote > > Ok I got the proof of concept down, but I can't get it all to run at once > > since Pharo realizes that the class does not exist(at the time of > > running), even though it will exist by the time it gets to that line. > > > > Is there a way to modify the following Transcript code make the following > > code run "one block at a time". Ignoring the fact that classes are not > > created at time of writing? > > > > I think I need some way to "reflectively find a class by class name at > > runtime". > > > steps.st > > > ([ > > SimpleSwitchMorph subclass: #LOCell > > instanceVariableNames: 'mouseAction' > > classVariableNames: '' > > package: 'PBE-LightsOut' > > ] value). > > > > > / > > <snip> > / > Well, that was an excruciating read. Did you find it easy to read? I'll bet > you also found it hard to write. > > If you look at the file-out format (also called chunk format), you can just > simply write the code you want as a result and it would be infinitely more > comprehensible to you and to those you would share it with. > > There are times when writing things along the lines that you have are > essential. For example, if you are writing a code generator you would want > to generate source strings and compile them. > > > > -- > View this message in context: http://forum.world.st/New-to- > Pharo-a-bunch-of-questions-tp4917701p4917927.html > Sent from the Pharo Smalltalk Developers mailing list archive at > Nabble.com. > >

Oct. 3, 2016

Re: [Pharo-dev] New to Pharo; a bunch of questions.

by Richard Sargent

CodeDmitry wrote > Ok I got the proof of concept down, but I can't get it all to run at once > since Pharo realizes that the class does not exist(at the time of > running), even though it will exist by the time it gets to that line. > > Is there a way to modify the following Transcript code make the following > code run "one block at a time". Ignoring the fact that classes are not > created at time of writing? > > I think I need some way to "reflectively find a class by class name at > runtime". > steps.st > ([ > SimpleSwitchMorph subclass: #LOCell > instanceVariableNames: 'mouseAction' > classVariableNames: '' > package: 'PBE-LightsOut' > ] value). > > / > <snip> / Well, that was an excruciating read. Did you find it easy to read? I'll bet you also found it hard to write. If you look at the file-out format (also called chunk format), you can just simply write the code you want as a result and it would be infinitely more comprehensible to you and to those you would share it with. There are times when writing things along the lines that you have are essential. For example, if you are writing a code generator you would want to generate source strings and compile them. -- View this message in context: http://forum.world.st/New-to-Pharo-a-bunch-of-questions-tp4917701p4917927.h… Sent from the Pharo Smalltalk Developers mailing list archive at Nabble.com.

Oct. 3, 2016

Re: [Pharo-dev] New to Pharo; a bunch of questions.

by Richard Sargent

CodeDmitry wrote > It's just nice to have a standalone code that I can give to my friends > that they can read and run to create the structure without having to setup > everything themselves, but at the same time not needing to use a package. > > A standalone script is quite elegant for situations like that, since it > well encapsulates the automation without forcing people to understand > packaging. > > I don't mind shooting myself in the foot, I want to understand how Pharo > runtime works, it has this strange circularity to it that I can't quite > wrap my mind around. > > I just like doing everything in Code if possible. I see no reason to use > the browser other to inspect system state at the moment. Bear in mind, the browsers were created by the original authors to facilitate repetitive actions. They are tools for interacting with the objects in the system, just as are the debugger and inspector. That being said, I do agree i is important to understand how the tools do what they do. You should definitely browse the Behavior hierarchy. It contains all the code for creating classes, compiling (and installing!) methods, removing methods, and so on. Also, I noticed in your examples that you like to write ([ ... ] value). Why? Why not just write the actual code (shown as ... in my example)? > Personally I've never had more fun with Smalltalk as I did writing this > proof of concept. -- View this message in context: http://forum.world.st/New-to-Pharo-a-bunch-of-questions-tp4917701p4917926.h… Sent from the Pharo Smalltalk Developers mailing list archive at Nabble.com.

Oct. 3, 2016

Re: [Pharo-dev] New to Pharo; a bunch of questions.

by Richard Sargent

CodeDmitry wrote > @askoh > > Ryerson University, Pragmatic Programming Languages teaches Smalltalk, and > Introduction to Object Oriented Programming does too. Well, be sure to check out the Toronto Smalltalk User Group! http://www.smalltalk.ca/ says they meet at Ryerson. I'm not sure that's always / still true. But you will be welcomed. > There was also a club I think where people did Smalltalk coding, but I > never really visited it so I may have been lied to. > > @stepharo > > heh you're right! I haven't noticed that feature, it's handy. > > Umm I created a category Dummy, with class Dumbo, with method meep that > does trivial text printing, and file-out'd it, but I don't know how to put > it back in, it's not a valid Playground-script. > > Object subclass: #Dumbo > instanceVariableNames: '' > classVariableNames: '' > poolDictionaries: '' > category: 'Dummy'! > > !Dumbo methodsFor: 'as yet unclassified' stamp: 'Anonymous 10/2/2016 > 21:19'! > meep > Transcript show: 'Hello, World!!'.! ! -- View this message in context: http://forum.world.st/New-to-Pharo-a-bunch-of-questions-tp4917701p4917925.h… Sent from the Pharo Smalltalk Developers mailing list archive at Nabble.com.

Oct. 3, 2016

How does Pharo store instance variables?

by CodeDmitry

I am trying to study Pharo's internals and I am now curious how it stores class variables. I notice that in order to have a class `Greeter` with a "static" variable `greeting`, I need to make `greeting` an instance variable under "show show the class side" and create a "Getter" and "Setter" for this "instance variable". First thing that confuses me is, why is this called an instance variable if this particular "static" method is not bound to any particular instance? Is it just because it is defined in an "instance" of a "ProtoClass"? Second thing that confuses me is, where are these pairs of ("instance variable name" => "instance variable value") stored? I know that I can call Transcript show: ((Greeter class) instanceVariables at: 1). which prints "greeting". and Transcript show: Greeter instanceVariables class. which prints "Array"(curious, i expected a Dictionary mapping Strings to Object). Transcript show: ((Greeter class) instanceVariables at: 1) class. prints "ByteSymbol". Now I am confused, where are the actual values of the "static variables" stored? I can find the names, but can't understand where the values are hidden. Can somebody help me understand this? -- View this message in context: http://forum.world.st/How-does-Pharo-store-instance-variables-tp4917924.html Sent from the Pharo Smalltalk Developers mailing list archive at Nabble.com.

Oct. 3, 2016

Re: [Pharo-dev] New to Pharo; a bunch of questions.

by stepharo

Excellent :) We did not know that Ryerson was using Pharo! Stef > @askoh > > Ryerson University, Pragmatic Programming Languages teaches smalltalk, and > Introduction to Object Oriented Programming does too. > > > > -- > View this message in context: http://forum.world.st/New-to-Pharo-a-bunch-of-questions-tp4917701p4917808.h… > Sent from the Pharo Smalltalk Developers mailing list archive at Nabble.com. > >

Oct. 3, 2016