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

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

by Ben Coman

Hi Dmitry, You've just bumped into one of Smalltalk's paradigms that may change the way you *think* about programming ;). For me it was certainly an eye-opener. It intrigued me there could even exist another way to *think* about booleans. On Mon, Oct 31, 2016 at 10:06 PM, jtuchel(a)objektfabrik.de <jtuchel(a)objektfabrik.de> wrote: > 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 ;-) Interesting insight. On Mon, Oct 31, 2016 at 10:32 PM, CodeDmitry <dimamakhnin(a)gmail.com> wrote: > 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. Not quite. Yes most of Boolean's own methods are mostly subclassResponsibilitys, but you can see Boolean provides a place for extensions by *Fuel, *Reflectivity, *ston-core and *UnifiedFFI packages to hang methods common to both True and False. The best way to properly understand this is to observe it in action yourself, by debugging through it. Except you can't debug it since #ifTrue:#iFalse is inlined for performance. Instead try defining... True>>myifTrue: trueAlternativeBlock ifFalse: falseAlternativeBlock ^trueAlternativeBlock value False>>myifTrue: trueAlternativeBlock ifFalse: falseAlternativeBlock ^falseAlternativeBlock value then from Playground, debug... true myifTrue: [self inform: 'true'] ifFalse: [self inform: 'false']. false myifTrue: [self inform: 'true'] ifFalse: [self inform: 'false']. and just continue stepping <Into>, (except step <Over> the #inform: when you get there) cheers -ben

Oct. 31, 2016

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

by Thierry Goubier

Le 31/10/2016 Ã 16:18, Denis Kudriashov a Ã©crit : > > 2016-10-31 16:11 GMT+01:00 Norbert Hartl <norbert(a)hartl.name > <mailto:norbert@hartl.name>>: > >> Am 31.10.2016 um 15:59 schrieb phil(a)highoctane.be >> <mailto:phil@highoctane.be>: >> >> but you should use myCollection ifEmpty: [ ... ] >> > Why? > > > because it shorter :) And when teaching Pharo, you have to explain: Student - What is ifEmpty: ? Teacher - It is the same as isEmpty ifTrue: [ ... Joke apart, it seems, following Esteban remark, that Pharo is gearing towards making life easier to the experienced Smalltalk developper (make it easier to create a collection-like object) and harder for newcomers ... Thierry

Oct. 31, 2016

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

by Denis Kudriashov

2016-10-31 16:11 GMT+01:00 Norbert Hartl <norbert(a)hartl.name>: > Am 31.10.2016 um 15:59 schrieb phil(a)highoctane.be: > > but you should use myCollection ifEmpty: [ ... ] > > Why? because it shorter :)

Oct. 31, 2016

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

by Esteban A. Maringolo

2016-10-31 12:11 GMT-03:00 Norbert Hartl <norbert(a)hartl.name>: > > Am 31.10.2016 um 15:59 schrieb phil(a)highoctane.be: > > but you should use myCollection ifEmpty: [ ... ] > > Why? It enables you to implement polymorphism with an object that might not be aCollection, but behaves like one. Of course you could also implement #isEmpty, but in my experience the less you test (#isEmpty) and the more you delegate (ifEmpty:) the better. :) Regards, Esteban A. Maringolo

Oct. 31, 2016

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

by CodeDmitry

I meant "dynamic" as a contrast to Java's abstract classes/interfaces which are going to slap you if you forget to implement one of the abstract methods, so the only reason to define the methods that are going to be overwritten seems to be to disambiguate the error message that will be raised from the selector not being there. -- View this message in context: http://forum.world.st/How-does-Boolean-ifTrue-work-tp4920873p4920905.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 Esteban A. Maringolo

2016-10-31 11:58 GMT-03:00 CodeDmitry <dimamakhnin(a)gmail.com>: > 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). I don't know what you mean by "dynamic". The whole object system of Smalltalk is dynamic by design. Esteban A. Maringolo

Oct. 31, 2016

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

by Norbert Hartl

> Am 31.10.2016 um 15:59 schrieb phil(a)highoctane.be: > > but you should use myCollection ifEmpty: [ ... ] > Why? Norbert > Phil > > On Mon, Oct 31, 2016 at 3:25 PM, Sven Van Caekenberghe <sven(a)stfx.eu <mailto:sven@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 <mailto:dimamakhnin@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 <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 Esteban A. Maringolo

2016-10-31 11:32 GMT-03:00 CodeDmitry <dimamakhnin(a)gmail.com>: > 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. Not exactly, look at the methods in Boolean and you'll see many methods are common to all. So Boolean has a reason to be the superclass of both True and False. Esteban A. Maringolo

Oct. 31, 2016

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

by Thierry Goubier

Le 31/10/2016 Ã 15:32, CodeDmitry a Ã©crit : > 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. Boolean is a nice header for classification. Everybody is familiar with Boolean algebra, including hardware guys :) > 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. Not exactly. Boolean carry 15 methods that are not overridden in either False nor True (and 11 methods which are), so Boolean is also used as a way to share code between the classes True and False and avoid code duplication. A nice case for having a common superclass below Object. Thierry

Oct. 31, 2016

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

by phil＠highoctane.be

For the full story, these objects and ifTrue: etc are special cases in the VM code. For speed. Phil On Mon, Oct 31, 2016 at 3:32 PM, CodeDmitry <dimamakhnin(a)gmail.com> wrote: > 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