walking through 3 code snippets

Walking Through 3 Code Snippets

AKA: Pointers and Scope are important

Code to Run Through

• Tanner’s Array#Each• Oleg’s Default Hash Modification• Marcus’ Blorgotron Closure Scope

Tanner’s Array#Each

fruits = %w{ orange apple strawberry banana mango }

fruits.count.times { |i| fruits[i] += " is delicious" }

fruits.each { |fruit| fruit += " is delicious" }

from http://bitsandbytesandallthingsnice.tumblr.com/post/25137722066/array-each-returns-same-array

Given this array

This works

But this doesn’t

http://bitsandbytesandallthingsnice.tumblr.com/post/25137722066/array-each-returns-same-array




fruits = %w{ orange apple mango }fruits.count.times do |i| fruits[i] += " is delicious" endfruits.each do |fruit| fruit += " is “delicious”end

Rewritten Slightly…

Tanner’s Array#Eachfruits = %w{ orange apple mango }fruits.count.times do |i| fruits[i] += " is delicious" endfruits.each do |fruit| fruit += " is delicious" }end

Track Variables Here

(AKA The Global Environment)

Tanner’s Array#Eachfruits = %w{ orange apple mango }fruits.count.times do |i| fruits[i] += " is delicious" endfruits.each do |fruit| fruit += " is delicious" }end

Variables Names Working Memory

Tanner’s Array#Eachfruits = %w{ orange apple mango }

orangeapplemango


orangeapplemango

[] 0 1 2


orangeapplemango

[] 0 1 2

fruits


orangeapplemango

[] 0 1 2

fruits

Sidenote: Order of OperationsIn Math• Parentheses First• Multiplication / Division• Addition / Subtraction

(5 + 3) + 12 * 4 / 2

8 + 48 / 2

8 + 24

32


orangeapplemango

[] 0 1 2

fruits

Sidenote: Order of OperationsIn Programming• Parentheses (arguments) first• Left to right• Assignment (=) is last

x = 3.add(5 + 2)

x = 3.add(7)

x = 10


orangeapplemango

[] 0 1 2

fruits

Sidenote: Order of OperationsIn Programming• Parentheses (arguments) first• Exceptions• Logic

• Left to right• Assignment (=) is last


orangeapplemango

[] 0 1 2

fruits

Sidenote: Order of OperationsIn Programming• Parentheses (arguments) first• Exceptions• Logic


puts (“something true” || something_illegal)


orangeapplemango

[] 0 1 2

fruits

Sidenote: Order of OperationsIn Programming• Parentheses (arguments) first• Exceptions• Logic• Function / Block Definitions



fruits = %w{ orange apple mango }fruits.count.times do |i| fruits[i] += " is delicious" end

Snippet 1: The one that works

Tanner’s Array#Eachfruits = %w{ orange apple mango }fruits.count.times do |i| fruits[i] += " is delicious" end

orangeapplemango

[] 0 1 2

fruits

Tanner’s Array#Eachfruits = %w{ orange apple mango }3.times do |i| fruits[i] += " is delicious" end

orangeapplemango

[] 0 1 2

fruits

Tanner’s Array#Eachfruits = %w{ orange apple mango }3.times do |i| fruits[i] = fruits[i] + " is delicious" end

orangeapplemango

[] 0 1 2

fruits

0


orangeapplemango

[] 0 1 2

fruits

0

i


orangeapplemango

[] 0 1 2

fruits

i

orange

0


orangeapplemango

[] 0 1 2

fruits

i

orange “ is delicious"

0


orangeapplemango

[] 0 1 2

fruits

i

orange “ is delicious"

0

orange is delicious

Tanner’s Array#Eachfruits = %w{ orange apple mango }3.times do |i| fruits[i] = fruits[i] + " is delicious"end

orangeapplemango

[] 0 1 2

fruits

i

orange is delicious

0


orangeapplemango

[] 0 1 2

fruits

i orange is delicious

i apple is delicious

i mango is delicious

0

1

2

Tanner’s Array#EachSnippet 2: The one that doesn’t work

fruits = %w{ orange apple mango }fruits.each do |fruit| fruit = fruit + " is delicious" end

Tanner’s Array#Eachfruits = %w{ orange apple mango }fruits.each do |fruit| fruit = fruit + " is delicious" end


orangeapplemango

[] 0 1 2

fruits


orangeapplemango

[] 0 1 2

fruits

orange


orangeapplemango

[] 0 1 2

fruits

orange

fruit

Tanner’s Array#Eachfruits = %w{ orange apple mango }fruits.each do |fruit| fruit = fruit + " is delicious"

end

orangeapplemango

[] 0 1 2

fruits

orange

fruit

orange is delicious


orangeapplemango

[] 0 1 2

fruits

orange

fruit

orange is delicious


orangeapplemango

[] 0 1 2

fruits

fruit orange is delicious

fruit apple is delicious

fruit mango is delicious


Let’s compare the two ways


This example does the work, but the work is unreachablefruits.each { |fruit| fruit += fruit " is delicious" }

orangeapplemango

[] 0 1 2

fruits

This example worksfruits.count.times {|i| fruits[i] += " is delicious" }

[] 0 1 2

fruits orange is delicious

apple is delicious

mango is delicious

fruit orange is delicious

fruit apple is delicious

fruit mango is delicious

Unreacha

ble!

Oleg’s Default Hash Modificationhsh = Hash.new(‘stuff’)hsh[“key”]hsh[“key”] << “stuff”hsh[“key”]hsh[“key”] = “something else”hsh[“key”]Hsh[“other_key”]

Oleg’s Default Hash Modificationhsh = Hash.new(‘stuff’)hsh[“key”]hsh[“key”] << “stuff”hsh[“key”]hsh[“key”] = “something else”hsh[“key”]hsh[“other_key”]

stuff


{}else

stuff


{}else

stuffhsh


{}else

stuffhsh

stuff


{}else

stuffhsh

stuff

<<


{}else

stuffhsh stuff


{}else

stuffhsh stuff

something else


{}keyelse

stuffhsh stuff

something else

Marcus’ Blorgotron Closure Scopevar Blorgotron = function() { var secret = Math.random(); return { get: function(){ return secret;}, inc: function(){secret++;} } }

blorg = Blorgotron()blorg.get()blorg.inc()blorg.get()

blorg2 = Blorgotron()blorg2.inc()

Marcus’ Blorgotron Closure Scope

0.53

var Blorgotron = function() { var secret = Math.random(); return { get: function(){ return secret;}, inc: function(){secret++;} } }




0.53secret





0.53secret




function(){return secret;}function(){secret++;}


0.53secret




{}getinc



0.53secret




{}getinc


blorg


0.53secret

var Blorgotron = function() { secret = Math.random(); return { get: function(){ return secret;}, inc: function(){secret++;} } }



{}getinc


blorg

blorg.get()

blorg[“get”]()

{get: function(){ return secret;}, inc: function(){secret++;} } }[“get”]()

function(){ return secret;}()

Evaluating blorg.get()


0.53secret




{}getinc


blorg


1.53secret




{}getinc


blorg


1.53secret




{}getinc


blorg 0.24secret{}getinc



1.53secret




{}getinc




blorg2

walking through 3 code snippets

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