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

Re: [Pharo-users] How does Boolean ifTrue work?

by phil＠highoctane.be

but you should use myCollection ifEmpty: [ ... ] Phil On Mon, Oct 31, 2016 at 3:25 PM, Sven Van Caekenberghe <sven(a)stfx.eu> wrote: > myCollection isEmpty ifTrue: [ self inform: 'The collection is empty' ]. > > First #isEmpty is sent to myCollection which results in either true or > false as value. > > Then #ifTrue: is sent to this value. > > Now, if the value was true (the sole instance of class True), the code in > True>>#ifTrue: is executed, which will evaluate the block by sending it > #value. If the value was false, the code in False>>#ifTrue: is executed, > and nil is returned and the block is not executed. > > Like others said, it is just polymorphism at work. > > (And yes, the compiler optimises some of this logic a bit, but the effect > is the same). > > > On 31 Oct 2016, at 14:58, CodeDmitry <dimamakhnin(a)gmail.com> wrote: > > > > But still, how is the actual argument "alternativeBlock" passed to the > > True/False from a Boolean? > > > > The message does not cache the message inside itself before passing the > > message, and it does not pass the alternative block along with the > message. > > > > > > > > -- > > View this message in context: http://forum.world.st/How- > does-Boolean-ifTrue-work-tp4920873p4920886.html > > Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com. > > > > > >

Oct. 31, 2016

Re: [Pharo-users] How does Boolean ifTrue work?

by CodeDmitry

Ah so it's more of a "dynamic abstract class" than a "dynamic interface", so they do get visited during the traversal of the inheritence chain(rather than skipped immediately to Object). -- View this message in context: http://forum.world.st/How-does-Boolean-ifTrue-work-tp4920873p4920896.html Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com.

Oct. 31, 2016

Re: [Pharo-users] How does Boolean ifTrue work?

by CodeDmitry

I realized it a bit before you posted but thanks for confirming. Boolean seems to indeed just be a "Dynamic Interface"; since Smalltalk does not have "Java Interfaces"(nor want them for the same reason JavaScript doesn't), the developers wanted to still have True and False be subclasses of Booleans. In all honesty Boolean seems to be there purely for the "common sense" of it, rather than need. Smalltalk is duck typed and has no need for interfaces. If it's a Boolean, you know it has those methods so Boolean is not actually useful for anything; True and False may as well just be subclasses of Object. -- View this message in context: http://forum.world.st/How-does-Boolean-ifTrue-work-tp4920873p4920891.html Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com.

Oct. 31, 2016

Re: [Pharo-users] How does Boolean ifTrue work?

by Sven Van Caekenberghe

myCollection isEmpty ifTrue: [ self inform: 'The collection is empty' ]. First #isEmpty is sent to myCollection which results in either true or false as value. Then #ifTrue: is sent to this value. Now, if the value was true (the sole instance of class True), the code in True>>#ifTrue: is executed, which will evaluate the block by sending it #value. If the value was false, the code in False>>#ifTrue: is executed, and nil is returned and the block is not executed. Like others said, it is just polymorphism at work. (And yes, the compiler optimises some of this logic a bit, but the effect is the same). > On 31 Oct 2016, at 14:58, CodeDmitry <dimamakhnin(a)gmail.com> wrote: > > But still, how is the actual argument "alternativeBlock" passed to the > True/False from a Boolean? > > The message does not cache the message inside itself before passing the > message, and it does not pass the alternative block along with the message. > > > > -- > View this message in context: http://forum.world.st/How-does-Boolean-ifTrue-work-tp4920873p4920886.html > Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com. >

Oct. 31, 2016

Re: [Pharo-users] How does Boolean ifTrue work?

by Thierry Goubier

Le 31/10/2016 Ã 14:58, CodeDmitry a Ã©crit : > But still, how is the actual argument "alternativeBlock" passed to the > True/False from a Boolean? > > The message does not cache the message inside itself before passing the > message, and it does not pass the alternative block along with the message. If I get correctly what you are saying, this is because the ifTrue:ifFalse: message is never sent to an instance of Boolean. It is sent either to true, the single instance of class True, or to false, the single instance of class False, where the implementation is what you expect: False>>#ifTrue:ifFalse: ifTrue: trueAlternativeBlock ifFalse: falseAlternativeBlock "Answer the value of falseAlternativeBlock. Execution does not actually reach here because the expression is compiled in-line." ^falseAlternativeBlock value If you're interested in the details, do also read the comment. Regards, Thierry

Oct. 31, 2016

Re: [Pharo-users] Spec: Setting rows height of a pictures list

by Nicolai Hess

2016-10-31 15:07 GMT+01:00 Matteo via Pharo-users < pharo-users(a)lists.pharo.org>: > > > ---------- Weitergeleitete Nachricht ---------- > From: Matteo <matteob8(a)yahoo.it> > To: Any question about pharo is welcome <pharo-users(a)lists.pharo.org> > Cc: > Date: Mon, 31 Oct 2016 15:06:27 +0100 > Subject: Re: [Pharo-users] Spec: Setting rows height of a pictures list > Thanks Nicolai, > > unfortunately, even using images of the same height I obtain a list > with thin rows. Maybe I'm typing something wrong. > > I'll try to figure out how to handle this. > Please let me know, if you have any further suggestion. > > Thanks, > Matteo > > For Images with the same height/width, you can use #buildWithSpecLayout: in the displayBlock and use a SpecTableLayout with the width/height of the image model image. But this doesn't really work, somehow the list widget can not handle the selection and scrolling (but the images are shown in full size) : imageModels := (1 to:10) collect:[:i | ImageModel new image: PolymorphSystemSettings pharoLogoForm]. listModel := ListModel new items: imageModels. listModel displayBlock:[:item | | layout | layout := SpecTableLayout row add:#yourself; height: item image height; width: item image width. item buildWithSpecLayout: layout]. listModel openWithSpec > > On 31/10/16 12:26, Nicolai Hess wrote: > > > > > > 2016-10-31 10:19 GMT+01:00 Matteo via Pharo-users > > <pharo-users(a)lists.pharo.org <mailto:pharo-users@lists.pharo.org>>: > > > > > > > > ---------- Weitergeleitete Nachricht ---------- > > From: Matteo <matteob8(a)yahoo.it <mailto:matteob8@yahoo.it>> > > To: "Pharo is welcome (ML)" <pharo-users(a)lists.pharo.org > > <mailto:pharo-users@lists.pharo.org>> > > Cc: > > Date: Mon, 31 Oct 2016 10:18:03 +0100 > > Subject: Spec: Setting rows height of a pictures list > > Hi, > > I've created a list of pictures, i.e. a widget based on > > ListModel where > > each item is a ImageModel. > > > > When the widget is displayed I get list window with very > > thin rows. > > > > Is there a way to control the ListModel rows height? > > > > > > Not if the images have different heights (you can, but it looks > > terrible, because the underlaying list morph does not work for list > > items with different heights). > > > > > > > > > > Thanks, > > Matteo > > > > > > > > >

Oct. 31, 2016

Re: [Pharo-users] Spec: Setting rows height of a pictures list

by Matteo

Thanks Nicolai, unfortunately, even using images of the same height I obtain a list with thin rows. Maybe I'm typing something wrong. I'll try to figure out how to handle this. Please let me know, if you have any further suggestion. Thanks, Matteo On 31/10/16 12:26, Nicolai Hess wrote: > > > 2016-10-31 10:19 GMT+01:00 Matteo via Pharo-users > <pharo-users(a)lists.pharo.org <mailto:pharo-users@lists.pharo.org>>: > > > > ---------- Weitergeleitete Nachricht ---------- > From: Matteo <matteob8(a)yahoo.it <mailto:matteob8@yahoo.it>> > To: "Pharo is welcome (ML)" <pharo-users(a)lists.pharo.org > <mailto:pharo-users@lists.pharo.org>> > Cc: > Date: Mon, 31 Oct 2016 10:18:03 +0100 > Subject: Spec: Setting rows height of a pictures list > Hi, > I've created a list of pictures, i.e. a widget based on > ListModel where > each item is a ImageModel. > > When the widget is displayed I get list window with very > thin rows. > > Is there a way to control the ListModel rows height? > > > Not if the images have different heights (you can, but it looks > terrible, because the underlaying list morph does not work for list > items with different heights). > > > > > Thanks, > Matteo > > >

Oct. 31, 2016

Re: [Pharo-users] How does Boolean ifTrue work?

by jtuchel＠objektfabrik.de

When I teach Smalltalk, this is one of the most beautiful exercises for students. Those who get it will love Smalltalk, those who don't often leave the project soon ;-) BTW: This is not a visitor or any other pattern, it really is just Polymorphism at work and the reason why back in the 90ies, people said if statements should be replaced by Polymorphism Joachim Am 31.10.16 um 14:17 schrieb CodeDmitry: > I am looking at > > ifTrue: alternativeBlock > "If the receiver is false (i.e., the condition is false), then the value is > the > false alternative, which is nil. Otherwise answer the result of evaluating > the argument, alternativeBlock. Create an error notification if the > receiver is nonBoolean. Execution does not actually reach here because > the expression is compiled in-line." > > self subclassResponsibility > > In order to perform the block, ifTrue must somehow end up evaluating the > block, but this code only sends a subclassResponsibility message to itself > and implicitly returns itself. > > Where does the block actually get evaluated? > > > > > -- > View this message in context: http://forum.world.st/How-does-Boolean-ifTrue-work-tp4920873.html > Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com. > > -- ----------------------------------------------------------------------- Objektfabrik Joachim Tuchel mailto:jtuchel@objektfabrik.de Fliederweg 1 http://www.objektfabrik.de D-71640 Ludwigsburg http://joachimtuchel.wordpress.com Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1

Oct. 31, 2016

Re: [Pharo-users] How does Boolean ifTrue work?

by CodeDmitry

But still, how is the actual argument "alternativeBlock" passed to the True/False from a Boolean? The message does not cache the message inside itself before passing the message, and it does not pass the alternative block along with the message. -- View this message in context: http://forum.world.st/How-does-Boolean-ifTrue-work-tp4920873p4920886.html Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com.

Oct. 31, 2016

Re: [Pharo-users] How does Boolean ifTrue work?

by Thierry Goubier

Hi Dmitry, you found it yourself, sort of! Le 31/10/2016 Ã 14:25, CodeDmitry a Ã©crit : > Wait, so unlike JavaScript; True and False are actual singletons and > ifTrue/ifFalse/ifTrue:ifFalse: uses visitor pattern to have the actual True > or False handle the block rather than doing it themselves? Yes, true and false are singletons (resp single instance of the True class, False class). No, this is not a visitor pattern, just polymorphism (True and False have their own implementation of ifTrue:/ifFalse:/ifTrue:ifFalse:/ifFalse:ifTrue:). Regards, Thierry

Oct. 31, 2016