Affordances in Programming Languages

From RubyConf 2014.

A good design communicates the intended use of the object. In the physical world, this communication is accomplished by "affordances" as discussed by Donald Norman in "The Psychology of Everyday Things".

Programming languages also have affordances, and they influence the kinds of solutions we develop. The more languages we know, the more we "expand our design space" so that we can come up with better solutions to the problems we face every day.

We will look at a few example problems and show how they can be solved using the affordances provided by different languages.

Transcript

1. Affordances in Programming Languages Randy Coulman Senior Software Engineer http://randycoulman.com @randycoulman randycoulman
2. William Lindeke - http://tcsidewalks.blogspot.com/2009/06/signs-of-times-14.html
3. Nicolas Nova - http://www.flickr.com/photos/nnova/2252222949/
4. Satu Kyröläinen - http://www.satukyrolainen.com/affordances/
5. Satu Kyröläinen - http://www.satukyrolainen.com/affordances/
6. Affordance A quality of an object or environment that allows someone to perform an action.
7. Yoni Alter - http://www.yoniishappy.com/Tube-escalators
8. Affordances and Software
9. Example Points Smalltalk -> Ruby
10. 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 )
11. http://images.cryhavok.org/d/25562-2/Polar+and+Cartesian+Bears.jpg
12. θ r sinθ r cosθ r x y http://upload.wikimedia.org/wikipedia/commons/7/78/Polar_to_cartesian.svg
13. 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 )
14. 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
15. 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
16. Affordance Named Constructors
17. 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 )
18. Example Find/Detect Smalltalk -> Ruby
19. # ( 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 "
20. [ 2 , 4 , 6 , 8 ] . f i n d { | n | n . o d d ? } # = > n i l
21. # ( 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 "
22. Affordance Multiple Blocks
23. [ 2 , 4 , 6 , 8 ] . f i n d ( - > { : n o n e } ) { | n | n . o d d ? } # = > : n o n e
24. 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
25. 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
26. 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?
27. 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."
28. Example Cleaning Up After Yourself C++ -> Ruby
29. http://www.kategreene.net/do-not-look-at-laser-with-remaining-eye/
30. 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 ;
31. # 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 ) ; }
32. $ . / 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 !
33. # 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 ) ; }
34. $ . / 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 !
35. # 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 ) ; }
37. Bill Bradford - https://www.flickr.com/photos/mrbill/149717137/
38. RAII Resource Acquisition Is Initialization Acquire resources in the constructor Release them in the destructor
39. # 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 ; }
40. # 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 ; }
41. $ . / 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 !
42. Affordance Deterministic Destructors
43. Ruby doesn't have deterministic destructors. So what can we do instead?
44. 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
45. Define a finalizer?
46. Blocks!
47. 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
48. 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
49. $ 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 !
50. Example Restoring State Emacs Lisp -> Ruby
51. ( 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 ) ) ) )
52. ( 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 ) ) ) )
53. Affordance Macros
54. 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
55. 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
56. More examples: Functional-ish Ruby by Kevin Buchanan
57. Example ImageReader Smalltalk -> Ruby
58. 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
59. 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 ]
60. Affordance Subclass Iteration
61. 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
62. 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
63. 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
64. 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
65. 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
66. 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
67. 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
68. $ 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
69. Another example: Inverting Dependencies by Andre Bernardes
70. Takeaways
71. Languages afford certain designs and inhibit others
72. Languages influence thought
73. Learning new languages will increase your "solution space"
74. Don't go too far
75. Want More?
76. Affordances series on my blog http://randycoulman.com/blog/categories/affordances/
77. Tom Stuart's Refactoring Ruby with Monads talk http://confreaks.com/videos/4154-gogaruco2014-refactoring-ruby-with-monads
78. Acknowledgements Zeal (http://www.codingzeal.com/)
79. 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
80. Questions?
81. Randy Coulman http://speakerrate.com/randycoulman http://www.speakerdeck.com/randycoulman http://randycoulman.com @randycoulman randycoulman