Affordances in Programming Languages

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Affordances in Programming Languages Randy Coulman Senior Software Engineer http://randycoulman.com @randycoulman randycoulman

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William Lindeke - http://tcsidewalks.blogspot.com/2009/06/signs-of-times-14.html

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Nicolas Nova - http://www.flickr.com/photos/nnova/2252222949/

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Satu Kyröläinen - http://www.satukyrolainen.com/affordances/

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Satu Kyröläinen - http://www.satukyrolainen.com/affordances/

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Affordance A quality of an object or environment that allows someone to perform an action.

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Yoni Alter - http://www.yoniishappy.com/Tube-escalators

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Affordances and Software

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Example Points Smalltalk -> Ruby

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c l a s s P o i n t d e f i n i t i a l i z e ( x , y ) @ x = x @ y = y e n d e n d P o i n t . n e w ( 3 , 4 )

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http://images.cryhavok.org/d/25562-2/Polar+and+Cartesian+Bears.jpg

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θ r sinθ r cosθ r x y http://upload.wikimedia.org/wikipedia/commons/7/78/Polar_to_cartesian.svg

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c l a s s P o i n t d e f i n i t i a l i z e ( x , y ) @ x = x @ y = y e n d e n d P o i n t . n e w ( 3 , 4 )

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P o i n t c l a s s > > x : a n X y : a Y ^ s e l f n e w i n i t i a l i z e X : a n X y : a Y P o i n t > > i n i t i a l i z e X : a n X y : a Y x : = a n X . y : = a Y P o i n t x : 3 y : 4

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P o i n t c l a s s > > r : r a d i u s t h e t a : a n g l e I n R a d i a n s ^ s e l f x : r a d i u s * a n g l e I n R a d i a n s c o s y : r a d i u s * a n g l e I n R a d i a n s s i n P o i n t r : 5 t h e t a : 0 . 9 2 7 2 9 5

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Affordance Named Constructors

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c l a s s P o i n t d e f s e l f . x y ( x , y ) n e w ( x , y ) e n d d e f s e l f . p o l a r ( r , t h e t a ) x y ( r * M a t h . c o s ( t h e t a ) , r * M a t h . s i n ( t h e t a ) ) e n d p r i v a t e _ c l a s s _ m e t h o d : n e w # . . . r e s t s a m e a s b e f o r e e n d P o i n t . x y ( 3 , 4 ) P o i n t . p o l a r ( 5 , 0 . 9 2 7 2 9 5 )

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Example Find/Detect Smalltalk -> Ruby

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# ( 2 4 6 8 ) d e t e c t : [ : e a c h | e a c h o d d ] " U n h a n d l e d e x c e p t i o n : E l e m e n t N o t F o u n d "

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[ 2 , 4 , 6 , 8 ] . f i n d { | n | n . o d d ? } # = > n i l

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# ( 2 4 6 8 ) d e t e c t : [ : e a c h | e a c h o d d ] i f N o n e : [ # n o n e ] " # n o n e "

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Affordance Multiple Blocks

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[ 2 , 4 , 6 , 8 ] . f i n d ( - > { : n o n e } ) { | n | n . o d d ? } # = > : n o n e

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Another example: a s s e r t _ d i f f e r e n c e in A c t i v e S u p p o r t : : T e s t i n g : : A s s e r t i o n s can take multiple blocks

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Linguistic Relativity a.k.a. The Sapir-Whorf Hypothesis "[T]he structure of a language affects the ways in which its respective speakers conceptualize their world ... or otherwise influences their cognitive processes." -- http://en.wikipedia.org/wiki/Linguistic_relativity

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When Code Cries Cory Foy at SCNA 2012 http://vimeo.com/53986875 What does a language allow you to say? What does a language force you to say?

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The Power and Philosophy of Ruby Matz at OSCON 2003 http://www.rubyist.net/~matz/slides/oscon2003/mgp00001.html "Languages are not only tools to communicate, but also tools to think."

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Example Cleaning Up After Yourself C++ -> Ruby

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http://www.kategreene.net/do-not-look-at-laser-with-remaining-eye/

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i f ( ( e r r = S S L F r e e B u f f e r ( & h a s h C t x ) ) ! = 0 ) g o t o f a i l ; i f ( ( e r r = R e a d y H a s h ( & S S L H a s h S H A 1 , & h a s h C t x ) ) ! = 0 ) g o t o f a i l ; i f ( ( e r r = S S L H a s h S H A 1 . u p d a t e ( & h a s h C t x , & c l i e n t R a n d o m ) ) ! = g o t o f a i l ; i f ( ( e r r = S S L H a s h S H A 1 . u p d a t e ( & h a s h C t x , & s e r v e r R a n d o m ) ) ! = g o t o f a i l ; i f ( ( e r r = S S L H a s h S H A 1 . u p d a t e ( & h a s h C t x , & s i g n e d P a r a m s ) ) ! = g o t o f a i l ; g o t o f a i l ; i f ( ( e r r = S S L H a s h S H A 1 . f i n a l ( & h a s h C t x , & h a s h O u t ) ) ! = 0 ) g o t o f a i l ; / / . . . f a i l : S S L F r e e B u f f e r ( & s i g n e d H a s h e s ) ; S S L F r e e B u f f e r ( & h a s h C t x ) ; r e t u r n e r r ;

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# i n c l u d e " s u p p o r t . h " # i n c l u d e < i o s t r e a m > v o i d f o o ( ) { R e s o u r c e * r e s o u r c e = a c q u i r e R e s o u r c e ( ) ; b a r ( r e s o u r c e ) ; i f ( b a z ( r e s o u r c e ) ! = 4 2 ) r e t u r n ; s t d : : c o u t < < " C o m p l e t e d s u c c e s s f u l l y ! " < < s t d : : e n d l ; r e l e a s e R e s o u r c e ( r e s o u r c e ) ; }

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$ . / b r o k e n A c q u i r i n g r e s o u r c e C a u g h t e x c e p t i o n : o o p s !

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# i n c l u d e " s u p p o r t . h " # i n c l u d e < i o s t r e a m > v o i d f o o ( ) { R e s o u r c e * r e s o u r c e = a c q u i r e R e s o u r c e ( ) ; t r y { b a r ( r e s o u r c e ) ; i f ( b a z ( r e s o u r c e ) = = 4 2 ) { s t d : : c o u t < < " C o m p l e t e d s u c c e s s f u l l y ! " < < s t d : : e n d l ; } } c a t c h ( s t d : : e x c e p t i o n & e ) { r e l e a s e R e s o u r c e ( r e s o u r c e ) ; t h r o w ; } r e l e a s e R e s o u r c e ( r e s o u r c e ) ; }

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$ . / w o r d y A c q u i r i n g r e s o u r c e R e l e a s i n g r e s o u r c e C a u g h t e x c e p t i o n : o o p s !

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No content

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Bill Bradford - https://www.flickr.com/photos/mrbill/149717137/

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RAII Resource Acquisition Is Initialization Acquire resources in the constructor Release them in the destructor

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# i n c l u d e " S a f e R e s o u r c e . h " # i n c l u d e " s u p p o r t . h " S a f e R e s o u r c e : : S a f e R e s o u r c e ( ) : r e s o u r c e ( a c q u i r e R e s o u r c e ( ) ) { } S a f e R e s o u r c e : : ~ S a f e R e s o u r c e ( ) { r e l e a s e R e s o u r c e ( r e s o u r c e ) ; } R e s o u r c e * S a f e R e s o u r c e : : g e t ( ) { r e t u r n r e s o u r c e ; }

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# i n c l u d e " S a f e R e s o u r c e . h " # i n c l u d e " s u p p o r t . h " # i n c l u d e < i o s t r e a m > v o i d f o o ( ) { S a f e R e s o u r c e r e s o u r c e ; b a r ( r e s o u r c e . g e t ( ) ) ; i f ( b a z ( r e s o u r c e . g e t ( ) ) ! = 4 2 ) r e t u r n s t d : : c o u t < < " C o m p l e t e d s u c c e s s f u l l y ! " < < s t d : : e n d l ; }

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$ . / r a i i A c q u i r i n g r e s o u r c e R e l e a s i n g r e s o u r c e C a u g h t e x c e p t i o n : o o p s !

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Affordance Deterministic Destructors

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Ruby doesn't have deterministic destructors. So what can we do instead?

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b e g i n .. e n s u r e everywhere? Like t r y .. f i n a l l y in Java

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Define a finalizer?

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Blocks!

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c l a s s S a f e R e s o u r c e d e f s e l f . a c q u i r e r e s o u r c e = s e l f . n e w y i e l d r e s o u r c e e n s u r e r e s o u r c e . r e l e a s e e n d d e f i n i t i a l i z e p u t s " A c q u i r i n g r e s o u r c e " @ r e s o u r c e = O b j e c t . n e w e n d d e f r e l e a s e p u t s " R e l e a s i n g r e s o u r c e " @ r e s o u r c e = n i l e n d

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r e q u i r e _ r e l a t i v e " s u p p o r t " r e q u i r e _ r e l a t i v e " s a f e _ r e s o u r c e " d e f f o o S a f e R e s o u r c e . a c q u i r e d o | r e s o u r c e | b a r ( r e s o u r c e ) r e t u r n u n l e s s b a z ( r e s o u r c e ) = = 4 2 p u t s " C o m p l e t e d s u c c e s s f u l l y ! " e n d e n d

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$ r u b y d r i v e r . r b A c q u i r i n g r e s o u r c e R e l e a s i n g r e s o u r c e C a u g h t e x c e p t i o n : o o p s !

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Example Restoring State Emacs Lisp -> Ruby

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( d e f u n d e l e t e - e n c l o s e d - t e x t ( ) " D e l e t e t e x t b e t w e e n a n y p a i r o f d e l i m i t e r s . " ( i n t e r a c t i v e ) ( s a v e - e x c u r s i o n ( l e t ( p 1 p 2 ) ( s k i p - c h a r s - b a c k w a r d " ^ ( [ < > " ) ( s e t q p 1 ( p o i n t ) ) ( s k i p - c h a r s - f o r w a r d " ^ ) ] < > " ) ( s e t q p 2 ( p o i n t ) ) ( d e l e t e - r e g i o n p 1 p 2 ) ) ) )

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( d e f m a c r o s a v e - e x c u r s i o n ( & b o d y ) ` ( l e t ( ( s a v e d - b u f f e r ( c u r r e n t - b u f f e r ) ) ( s a v e d - p o i n t ( p o i n t - m a r k e r ) ) ( s a v e d - m a r k ( c o p y - m a r k e r ( m a r k - m a r k e r ) ) ) ) ( u n w i n d - p r o t e c t ( p r o g n , @ b o d y ) ( s e t - b u f f e r s a v e d - b u f f e r ) ( g o t o - c h a r s a v e d - p o i n t ) ( s e t - m a r k e r ( m a r k - m a r k e r ) s a v e d - m a r k e r ) ) ) )

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Affordance Macros

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d e f s a v e _ e x c u r s i o n s a v e d _ b u f f e r = c u r r e n t _ b u f f e r s a v e d _ p o i n t = p o i n t _ m a r k e r s a v e d _ m a r k = c o p y _ m a r k e r ( m a r k _ m a r k e r y i e l d e n s u r e s e t _ b u f f e r ( s a v e d _ b u f f e r ) g o t o _ c h a r ( s a v e d _ p o i n t ) s e t _ m a r k e r ( m a r k _ m a r k e r , s a v e d _ m a r k e r e n d

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d e f d e l e t e _ e n c l o s e d _ t e x t s a v e _ e x c u r s i o n d o s k i p _ c h a r s _ b a c k w a r d ( " ^ ( [ < > " ) p 1 = p o i n t s k i p _ c h a r s _ f o r w a r d ( " ^ ) ] < > " ) p 2 = p o i n t d e l e t e _ r e g i o n ( p 1 , p 2 ) e n d e n d

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More examples: Functional-ish Ruby by Kevin Buchanan

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Example ImageReader Smalltalk -> Ruby

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I m a g e R e a d e r c l a s s > > f r o m F i l e : a F i l e n a m e | r e a d e r C l a s s i m a g e S t r e a m r e a d e r | i m a g e S t r e a m : = a F i l e n a m e r e a d S t r e a m b i n a r y . [ r e a d e r C l a s s : = s e l f r e a d e r C l a s s F o r : i m a g e S t r e a m . r e a d e r C l a s s i f N i l : [ ^ s e l f e r r o r : ' U n k n o w n i m a g e t y p e : ' , a F i l e n a m e a s S t r i n g ] . r e a d e r : = r e a d e r C l a s s o n : i m a g e S t r e a m ] e n s u r e : [ i m a g e S t r e a m c l o s e ] . ^ r e a d e r

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I m a g e R e a d e r c l a s s > > r e a d e r C l a s s F o r : i m a g e S t r e a m ^ s e l f s u b c l a s s e s d e t e c t : [ : e a c h C l a s s | i m a g e S t r e a m r e s e t . [ e a c h C l a s s c a n R e a d : i m a g e S t r e a m ] e n s u r e : [ i m a g e S t r e a m r e s e t ] ] i f N o n e : [ n i l ]

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Affordance Subclass Iteration

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c l a s s I m a g e R e a d e r d e f s e l f . r e a d ( f i l e n a m e ) F i l e . o p e n ( f i l e n a m e , " r b " ) d o | i o | r e a d e r _ c l a s s = f i n d _ r e a d e r _ c l a s s ( i o ) r a i s e " U n k n o w n i m a g e t y p e : # { f i l e n a m e } " u n l e s s r e a d e r _ c l a s s r e a d e r _ c l a s s . n e w ( i o ) e n d e n d # . . . e n d

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c l a s s I m a g e R e a d e r # . . . d e f s e l f . f i n d _ r e a d e r _ c l a s s ( i o ) s u b c l a s s e s . f i n d { | r e a d e r | b e g i n i o . r e w i n d r e a d e r . c a n _ r e a d ? ( i o ) e n s u r e i o . r e w i n d e n d } e n d # . . . e n d

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c l a s s I m a g e R e a d e r # . . . d e f s e l f . i n h e r i t e d ( s u b c l a s s ) s u b c l a s s e s < < s u b c l a s s e n d d e f s e l f . s u b c l a s s e s @ s u b c l a s s e s | | = [ ] e n d # . . . e n d

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c l a s s B M P I m a g e R e a d e r < I m a g e R e a d e r d e f s e l f . c a n _ r e a d ? ( i o ) i o . r e a d ( 2 ) = = " B M " e n d d e f r e a d _ i m a g e p u t s " R e a d i n g B M P " e n d e n d

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c l a s s J P G I m a g e R e a d e r < I m a g e R e a d e r d e f s e l f . c a n _ r e a d ? ( i o ) i o . r e a d ( 2 ) = = " \ x F F \ x D 8 " . b e n d d e f r e a d _ i m a g e p u t s " R e a d i n g J P G " e n d e n d

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c l a s s P N G I m a g e R e a d e r < I m a g e R e a d e r d e f s e l f . c a n _ r e a d ? ( i o ) i o . r e a d ( 8 ) = = " \ x 8 9 P N G \ r \ n \ x 1 A \ n " . b e n d d e f r e a d _ i m a g e p u t s " R e a d i n g P N G " e n d e n d

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r e q u i r e _ r e l a t i v e " i m a g e _ r e a d e r s " % w { b m p j p g p n g } . e a c h d o | e x t | I m a g e R e a d e r . r e a d ( " e x a m p l e . # { e x t } " ) e n d

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$ r u b y s u b c l a s s e s . r b R e a d i n g B M P R e a d i n g J P G R e a d i n g P N G

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Another example: Inverting Dependencies by Andre Bernardes

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Takeaways

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Languages afford certain designs and inhibit others

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Languages influence thought

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Learning new languages will increase your "solution space"

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Don't go too far

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Want More?

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Affordances series on my blog http://randycoulman.com/blog/categories/affordances/

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Tom Stuart's Refactoring Ruby with Monads talk http://confreaks.com/videos/4154-gogaruco2014-refactoring-ruby-with-monads

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Acknowledgements Zeal (http://www.codingzeal.com/)

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References The Design of Every Day Things - Donald Norman Linguistic Relativity - Wikipedia article When Code Cries - Cory Foy at SCNA 2012 The Power and Philosophy of Ruby - Matz at OSCON 2003 Inverting Dependencies - Andre Bernardes Functional-ish Ruby - Kevin Buchanan

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Questions?

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Randy Coulman http://speakerrate.com/randycoulman http://www.speakerdeck.com/randycoulman http://randycoulman.com @randycoulman randycoulman