4: Rails-Flavored Ruby in Java

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4: Rails-Flavored Ruby
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>> flash = { :success => "It worked!", :error => "It failed :-(" } => {:success=>"It worked!", :error=>"It failed :-("} >> flasheach do |key, value| > puts "Key #{keyinspect} has value #{valueinspect}" >> end Key :success has value "It worked!" Key :error has value "It failed :-("
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Note that, while the each method for arrays takes a block with only one variable, each for hashes takes two, a key and a value Thus, the each method for a hash iterates through the hash one key-value pair at a time The last example uses the useful inspect method, which returns a string with a literal representation of the object it s called on:
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>> puts (15)to_a # Put an array as a string 1 2 3 4 5 >> puts (15)to_ainspect # Put a literal array [1, 2, 3, 4, 5] >> puts :name, :nameinspect name :name >> puts "It worked!", "It worked!"inspect It worked! "It worked!"
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By the way, using inspect to print an object is common enough that there s a shortcut for it, the p function:
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>> p :name :name # Same as 'puts :nameinspect'
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434 CSS Revisited
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It s time now to revisit the lines from Listing 44 used in the layout to include the cascading style sheets:
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<%= stylesheet_link_tag 'blueprint/screen', :media => 'screen' %> <%= stylesheet_link_tag 'blueprint/print', :media => 'print' %>
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We are now nearly in a position to understand this As mentioned briefly in Section 412, Rails defines a special function to include stylesheets, and
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stylesheet_link_tag 'blueprint/screen', :media => 'screen'
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is a call to this function But there are two mysteries First, where are the parentheses In Ruby, they are optional; these two lines are equivalent:
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# Parentheses on function calls are optional stylesheet_link_tag('blueprint/screen', :media => 'screen') stylesheet_link_tag 'blueprint/screen', :media => 'screen'
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Second, the :media argument sure looks like a hash, but where are the curly braces When hashes are the last argument in a function call, the curly braces are optional; these two lines are equivalent:
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# Curly braces on final hash arguments are optional stylesheet_link_tag 'blueprint/screen', { :media => 'screen' } stylesheet_link_tag 'blueprint/screen', :media => 'screen'
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So, we see now that each of the lines
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<%= stylesheet_link_tag 'blueprint/screen', :media => 'screen' %> <%= stylesheet_link_tag 'blueprint/print', :media => 'print' %>
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calls the stylesheet_link_tag function with two arguments: a string, indicating the path to the stylesheet, and a hash, indicating the media type ( screen for the computer screen and print for a printed version) Because of the <%= %> brackets, the results are inserted into the template by ERb, and if you view the source of the page in your browser you should see the HTML needed to include a stylesheet (Listing 46)14
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14 You may see some funky numbers, like 1257465942, after the CSS filenames These are inserted by Rails to ensure that browsers reload the CSS when it changes on the server
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Listing 46 The HTML source produced by the CSS includes
4: Rails-Flavored Ruby
<link href="/stylesheets/blueprint/screencss" media="screen" rel="stylesheet" type="text/css" /> <link href="/stylesheets/blueprint/printcss" media="print" rel="stylesheet" type="text/css" />
44 Ruby Classes
We ve said before that everything in Ruby is an object, and in this section we ll finally get to define some of our own Ruby, like many object-oriented languages, uses classes to organize methods; these classes are then instantiated to create objects If you re new to object-oriented programming, this may sound like gibberish, so let s look at some concrete examples
441 Constructors
We ve seen lots of examples of using classes to instantiate objects, but we have yet to do so explicitly For example, we instantiated a string using the double quote characters, which is a literal constructor for strings:
>> => >> => s = "foobar" "foobar" sclass String # A literal constructor for strings using double quotes
We see here that strings respond to the method class, and simply return the class they belong to Instead of using a literal constructor, we can use the equivalent named constructor, which involves calling the new method on the class name:15