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10things.pdf.html
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<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>10 Things Every Java Programmer Should Know About Ruby</title>
<style>
html, body { margin: 0; padding: 0; }
body { font-family: Verdana, Geneva, Arial, Helvetica, sans-serif; }
a:link, a:visited { color: black; }
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h2 { font-size: 28pt; }
h3 { font-size: 25pt; }
p, li, dt, dd, td, th { font-size: 18pt; }
pre { font-size: 14pt; }
pre.small { font-size: 11pt; }
pre.code {
background-color: azure;
padding: 5px;
}
ul { list-style-type: square; }
.center { text-align: center; }
.slide { page-break-after: always;
min-height: 100mm;
padding: 40px;
border: 1px dotted black;
/*
background: -moz-linear-gradient( top, maroon, red);
*/
}
body { font-family: Helvetica; }
h1, h2, h3, h4, h5, h6 { color: #0050B0; }
h1 { text-align: center; }
/* todo: use pre.class - needs to get added using @@@lang */
pre {
background-color: white;
border: 2px solid #B05000;
padding: 10px;
}
div.code {
background-color: white;
border: 2px solid #B05000;
padding: 10px;
}
div.code pre {
background-color: white;
border: 0;
padding: 5px;
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for princexml (CSS3 paged media support)
@page { size: A4 landscape }
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</style>
</head>
<body>
<div class="presentation">
<div class='slide '>
<!-- === begin markdown block =====================================================
generated by markdown 1.0.0 on Ruby 1.9.2 (2011-07-09) [i386-mingw32]
on 2013-06-21 19:57:13 +0200 with Markdown engine kramdown (1.0.2)
using options { !to be done! }
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<!-- _S9SLIDE_ -->
<h1 id="things-every-java-programmer-should-know-about-ruby">10 Things Every Java Programmer Should Know About Ruby</h1>
<p class="center">Jim Weirich</p>
<p class="center">Adapted S6/S9 Version <sup>1</sup> from <a href="http://onestepback.org/articles/10things">Original Slide Deck</a></p>
<!-- begin help -->
<div class="help projection">
<p><strong>Slide Show Keyboard Controls (Help)</strong></p>
<table>
<tr>
<td> Action </td>
<td> Key </td>
</tr>
<tr>
<td> Go to next slide </td>
<td> Space Bar, Right Arrow, Down Arrow, Page Down, Click Heading </td>
</tr>
<tr>
<td> Go to previous slide </td>
<td> Left Arrow, Up Arrow, Page Up </td>
</tr>
<tr>
<td> Toggle between slideshow and outline view (Ø) </td>
<td> T </td>
</tr>
<tr>
<td> Show/hide slide controls (Ø « ») </td>
<td> C, Move mouse to bottom right corner </td>
</tr>
<tr>
<td> Zoom in, zoom out, zoom reset (100%) </td>
<td> Control<code>+</code>Plus, Control<code>+</code>Minus, Control<code>+</code><code>0</code> </td>
</tr>
</table>
</div>
<!-- end help -->
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="who-am-i">Who Am I?</h1>
<ul>
<li>Jim Weirich</li>
<li>Consultant for Compuware</li>
<li>Java Programmer</li>
<li>Ruby Enthusiast</li>
</ul>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="first-things-first">First Things First</h1>
<p>I used to teach an after hours course in C programming for employees of a large manufacturing company.
It was pretty easy to tell what programming languages the students had used previously just
by looking at the style of C code they produced. It is certainly true that
“You can write FORTRAN in any language”.</p>
<p>Java programmers investigating Ruby will find a language that look similar in many ways.
There are classes and modules, namespaces and scopes, instance variables and methods.
A Java programmer will feel quite at home in this Object Oriented language.</p>
<p>So the temptation will be to continue to program in a Java-style.
Sure, there are some things that are different (the lack of type declarations will probably
be the first thing that strikes them).
But nothing that can’t be worked around with a little effort … and they will miss a golden opportunity.</p>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="sapir-whorf-hypothesis">Sapir-Whorf Hypothesis</h1>
<p>The Sapir-Whorf Hypothesis theorizes that thoughts and behavior are determined
(or are at least partially influenced) by language. […] To this day it has not been completely
disputed or defended, but has continued to intrigue researchers around the world.</p>
<h3 id="quote">Quote</h3>
<blockquote>
<p>A language that doesn’t affect the way you think about programming
is not worth knowing – Alan Perlis </p>
</blockquote>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="the-ruby-way">The Ruby Way</h1>
<p>This is <em>not</em> yet another “Ruby is better than Java” article.
Nor is it intended to bash Java or Java programmers.
Rather, it is an attempt to aid Java programmers who are investigating Ruby
by helping them quickly get over the “<em>Writing Java in Ruby</em>” syndrome and to discover the Ruby Way.</p>
<p>Now, on to our 10 Things…</p>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="item-10---learn-ruby-conventions">Item #10 - Learn Ruby Conventions</h1>
<ul>
<li><code>ClassNames</code></li>
<li><code>method_names</code> and <code>variable_names</code></li>
<li><code>methods_asking_a_question?</code></li>
<li><code>slightly_dangerous_methods!</code></li>
<li><code>@instance_variables</code></li>
<li><code>$global_variables</code></li>
<li><code>SOME_CONSTANTS</code> or <code>OtherConstants</code></li>
</ul>
<p>Some of the conventions are enforced by the language,
others are merely standards used by the community.</p>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="item-9---everything-is-an-object">Item #9 - Everything is an Object</h1>
<p>Everything in Ruby that can be bound to a variable name
is a full-fledged object.</p>
<p>This has interesting consequences</p>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="classes-are-objects">Classes are Objects!</h1>
<ul>
<li><code>Array</code> is a constant name that is bound to the Array class object.</li>
<li>
<p>Creating new objects does not require special syntax. We just send <code>new</code> to the class object.
{: .clear}<!-- workaround: note - list includes code block with block attribute --></p>
<p>a = Array.new</p>
</li>
</ul>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="this-make-factories-trivial">This make factories trivial</h1>
<p>Since Classes create instances of themselves,
they are the ultimate factory object.</p>
<pre><code>def create_from_factory(factory)
factory.new
end
obj = create_from_factory(Array)
</code></pre>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="no-primitives">No Primitives!</h1>
<p>Even integers are full fledged objects.</p>
<pre><code>0.zero? # => true
1.zero? # => false
1.abs # => 1
-1.abs # => 1
1.methods # => list of methods for object 1
2.+(3) # => 5 (same as 2+3)
10.class # => Fixnum
(10**100).class
# => Bignum
</code></pre>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="nil-is-an-object"><code>nil</code> is an Object!</h1>
<ul class="clear">
<li>Java:
<ul>
<li><code>null</code> means “no reference to object”</li>
<li>Invoking a method on <code>null</code> is an error</li>
</ul>
</li>
<li>Ruby:
<ul>
<li><code>nil</code> is a normal object</li>
<li>You can never get a null pointer error!</li>
</ul>
</li>
</ul>
<pre><code>a = nil
a.nil? # => true
a.methods # => list of methods
a.abs # => NoMethodError
</code></pre>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="things-that-are-not-objects">Things that are not Objects</h1>
<ul>
<li>Variable names are not objects
<ul>
<li>You cannot have a variable reference another variable
<ul>
<li>(no indirection to variables)</li>
</ul>
</li>
<li>There are workarounds to this
<ul>
<li>But that’s an advanced topic</li>
<li>And no one really <em>needs</em> it anyways.</li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="more-things-that-are-not-objects">More Things that are not Objects</h1>
<ul class="clear">
<li>Blocks are not objects
<ul>
<li>But that’s a distinction without a difference</li>
<li>By the time you need them, they automatically convert to <code>Proc</code> objects</li>
</ul>
</li>
</ul>
<!-- begin left {:class=>"code"} -->
<div class="code">
<table width="100%"><tr><td width="50%" style="vertical-align: top;">
<pre><code>def with_block
yield
end
with_block {
# Never converted
}
</code></pre>
</td>
<!-- end left -->
<!-- begin right {:class=>"code"} -->
<td width="50%" style="vertical-align: top;">
<pre><code>def with_proc(&block)
block.call
end
with_proc {
# Converted internally
}
</code></pre>
</td></tr></table>
</div>
<!-- end right -->
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="item-8---almost-everything-is-a-message">Item #8 - (Almost) Everything is a Message</h1>
<p>All computation in Ruby happens through:</p>
<ul>
<li>Binding names to objects (assignment)</li>
<li>Primitive controls structures (e.g. <code>if</code>/<code>else</code>, <code>while</code>) and operators (e.g. <code>defined?</code>)</li>
<li>Sending messages to objects</li>
</ul>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="yes-all-of-these-are-messages">Yes, all of these are messages…</h1>
<dl>
<dt><code>string.index("x")</code></dt>
<dd>Send <code>:index</code> (with argument “<code>x</code>”)</dd>
<dt><code>string.length</code></dt>
<dd>Send <code>:length</code> (with no argument)</dd>
<dt><code>run_status_reports</code></dt>
<dd>Send <code>:run_status_reports</code> (to <code>self</code>)</dd>
<dt><code>1 + 2</code></dt>
<dd>Send <code>:+</code> (with argument <code>2</code>) to the object <code>1</code></dd>
<dt><code>array[i]</code></dt>
<dd>Send <code>:[]</code> (with argument <code>i</code>) to the array</dd>
</dl>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="messages-not-function-calls">Messages, not Function Calls</h1>
<p>Java Programmers tend to think of <code>obj.method()</code> as looking up
a member function in a table and calling it.</p>
<p>Ruby programmers tend to think of <code>obj.method</code> as sending a message
to an object.</p>
<p class="center">What’s the Difference?</p>
<p>The difference is subtle, but important!</p>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="what-kind-of-differences">What <em>Kind</em> of Differences?</h1>
<p>Consider the following class.
It defines an object that is able to record all the messages ever sent to it, and then playback those messages to another object.</p>
<pre><code>class VCR
def initialize
@messages = []
end
def method_missing(method, *args, &block)
@messages << [method, args, block]
end
def play_back_to(obj)
@messages.each do |method, args, block|
obj.send(method, *args, &block)
end
end
end
</code></pre>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="playing-back-data">Playing Back Data</h1>
<p>Example Code</p>
<pre><code>require 'src/vcr'
vcr = VCR.new
vcr.sub!(/Java/) { "Ruby" }
vcr.upcase!
vcr[11,5] = "Universe"
vcr << "!"
string = "Hello Java World"
puts string
vcr.play_back_to(string)
puts string
</code></pre>
<p>Output</p>
<pre><code>Hello Java World
HELLO RUBY Universe!
</code></pre>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="message-opportunities">Message Opportunities…</h1>
<dl>
<dt><strong>Remote Proxies</strong></dt>
<dd>Automatically forward any message to a remote object.</dd>
<dt><strong>Auto Loaders</strong></dt>
<dd>Stand in for an object until it gets its first message. Then load it and act like a regular proxy. Great for autoloading database backed objects.</dd>
<dt><strong>Decorators</strong></dt>
<dd>Intercept the messages you want and pass the rest through.</dd>
<dt><strong>Mock Objects</strong></dt>
<dd>Just write the methods that need to be mocked. Proxy or ignore the others as needed.</dd>
<dt><strong>Builders</strong></dt>
<dd>Generate XML/HTML/Whatever based on the methods called on the builder</dd>
</dl>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="item-7---ruby-is-way-more-dynamic-than-you-expect">Item #7 - Ruby is <em>Way</em> More Dynamic Than You Expect</h1>
<p>One of the big attractions of Java over C++ was the dynamic features
of the language. You could easily load classes at run time,
query objects about their classes and methods,
and even call methods discovered at runtime. </p>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="dynamic-beyond-java">Dynamic Beyond Java</h1>
<p>Ruby takes dynamic behavior several steps beyond Java.</p>
<!-- begin left {} -->
<table width="100%"><tr><td width="50%" style="vertical-align: top;">
<ul>
<li><code>method_missing</code></li>
<li>Easy Reflection</li>
<li>Open Classes</li>
</ul>
</td>
<!-- end left -->
<!-- begin right {} -->
<td width="50%" style="vertical-align: top;">
<ul>
<li>Singleton Objects</li>
<li>Definition Hooks</li>
<li>Code Evalutation</li>
</ul>
</td></tr></table>
<!-- end right -->
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="easy-reflection-create-object">Easy Reflection: Create Object</h1>
<pre><code>public static Object create(Class c, String value)
throws Exception
{
Constructor ctor = c.getConstructor(
new Class[] { String.class } );
return ctor.newInstance( new Object[] { "Hello" } );
}
public static void main (String args[])
throws Exception
{
Greeting g =(Greeting) create(Greeting.class, "Hello");
g.show();
}
</code></pre>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="easy-reflection">Easy Reflection</h1>
<p>The Ruby Version</p>
<pre><code>def create(klass, value)
klass.new(value)
end
g = create(Greeting, "Hello")
g.show
</code></pre>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="open-classes">Open Classes</h1>
<p>Methods can be added to classes at any point … even built in classes. </p>
<pre><code>class Integer
def even?
(self % 2) == 0
end
end
p (1..10).select { |n| n.even? }
# => [2, 4, 6, 8, 10]
</code></pre>
<p>Caution is advised, but this feature can be very useful.</p>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="singleton-methods">Singleton Methods</h1>
<p>Singleton methods are defined on individual objects, not classes.</p>
<pre><code>class Dog
end
rover = Dog.new
fido = Dog.new
def rover.speak
puts "Red Rover"
end
rover.speak # => "Red Rover"
fido.speak # => NoMethodError
</code></pre>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="hooks">Hooks</h1>
<p>Hooks allow the user to gain control at interesting moments
during the execution of a program.</p>
<pre><code>class MyClass
def MyClass.method_added(name)
puts "Adding Method #{name}"
end
def new_method
# Yada yada yada
end
end
</code></pre>
<p>Output</p>
<pre><code>Adding Method new_method
</code></pre>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="code-eval">Code Eval</h1>
<pre><code>class Module
def trace_attr(sym)
self.module_eval %{
def #{sym}
printf "Accessing %s with value %s\n",
"#{sym}", @#{sym}.inspect
@#{sym}
end
}
end
end
class Dog
trace_attr :name
def initialize(string)
@name = string
end
end
Dog.new("Fido").name # => Accessing name with value "Fido"
</code></pre>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="item-6---objects-are-strongly-typed---not-statically-typed">Item #6 - Objects are Strongly Typed - Not Statically Typed</h1>
<p class="center"><em>What is a Type?</em></p>
<p class="center">A type is<br />
<strong>a set of values</strong><br />
and<br />
<strong>a set of operations</strong> </p>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<!-- begin left {} -->
<table width="100%"><tr><td width="50%" style="vertical-align: top;">
<h3 id="c-code-weak">C Code (Weak)</h3>
<pre><code>#include <stdio.h>
extern float two();
int main() {
float x = 1.5 + two();
printf("%f\n", x);
printf("%d\n", x);
return 0;
}
</code></pre>
</td>
<!-- end left -->
<!-- begin right {} -->
<td width="50%" style="vertical-align: top;">
<h3 id="java-code-strong">Java Code (Strong)</h3>
<pre><code>public class Main {
public static
void main (String args[]) {
double x = 1.5 + Two.two();
System.out.println(x);
}
}
</code></pre>
</td></tr></table>
<!-- end right -->
<!-- begin left {} -->
<table width="100%"><tr><td width="50%" style="vertical-align: top;">
<pre><code>int two() { return 2; }
</code></pre>
</td>
<!-- end left -->
<!-- begin right {} -->
<td width="50%" style="vertical-align: top;">
<pre><code>public class Two {
public static int two() {
return 2;
}
}
</code></pre>
</td></tr></table>
<!-- end right -->
<!-- begin left {} -->
<table width="100%"><tr><td width="50%" style="vertical-align: top;">
<h3 id="output">Output</h3>
<pre><code>nan
0
</code></pre>
</td>
<!-- end left -->
<!-- begin right {} -->
<td width="50%" style="vertical-align: top;">
<h3 id="output-1">Output</h3>
<pre><code>3.5
</code></pre>
</td></tr></table>
<!-- end right -->
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<!-- begin left {} -->
<table width="100%"><tr><td width="50%" style="vertical-align: top;">
<h3 id="ruby-code-">Ruby Code (?)</h3>
<pre class="clear"><code>require 'two'
x = 1.5 + two
puts x
printf "%d", x
</code></pre>
<pre><code>def two
2
end
</code></pre>
<h3 id="output-2">Output</h3>
<pre><code>3.5
3
</code></pre>
</td>
<!-- end left -->
<!-- begin right {} -->
<td width="50%" style="vertical-align: top;">
<h3 id="so-what-makes-a-language-type-safe">So what makes a language type safe?</h3>
<ul>
<li>Compiler knowledge of the variable types?</li>
<li>Declaring all variables?</li>
<li>Compiler catching all type errors?</li>
</ul>
<p>Or…</p>
<!-- begin step {} -->
<div class="step">
<ul>
<li>Catching all inappropriate operations on a type, either at
<ul>
<li>compile time, or</li>
<li>run time</li>
</ul>
</li>
</ul>
</div>
<!-- end step -->
</td></tr></table>
<!-- end right -->
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<!-- begin left {} -->
<table width="100%"><tr><td width="50%" style="vertical-align: top;">
<h3 id="ruby-code">Ruby Code</h3>
<pre><code>def factorial(n)
result = 1
(2..n).each do |i|
result *= i
end
result
end
puts factorial(20)
puts factorial(21)
</code></pre>
</td>
<!-- end left -->
<!-- begin right {} -->
<td width="50%" style="vertical-align: top;">
<h3 id="java-code">Java Code</h3>
<pre><code>public class Fact {
static long factorial(long n) {
long result = 1;
for (long i=2; i<=n; i++)
result *= i;
return result;
}
public static
void main (String args[]) {
System.out.println(factorial(20));
System.out.println(factorial(21));
}
}
</code></pre>
</td></tr></table>
<!-- end right -->
<!-- begin left {} -->
<table width="100%"><tr><td width="50%" style="vertical-align: top;">
<h3 id="output-3">Output</h3>
<pre><code>2432902008176640000
51090942171709440000
</code></pre>
</td>
<!-- end left -->
<!-- begin right {} -->
<td width="50%" style="vertical-align: top;">
<h3 id="output-4">Output</h3>
<pre><code>2432902008176640000
-4249290049419214848
</code></pre>
</td></tr></table>
<!-- end right -->
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="lanaguage-typing-systems">Lanaguage Typing Systems</h1>
<!-- begin left {} -->
<table width="100%"><tr><td width="50%" style="vertical-align: top;">
<h3 id="java-is">Java is</h3>
<ul>
<li>Strongly,</li>
<li>Statically,</li>
<li>Manifestly</li>
</ul>
<p>typed.</p>
</td>
<!-- end left -->
<!-- begin right {} -->
<td width="50%" style="vertical-align: top;">
<h3 id="ruby-is">Ruby is</h3>
<ul>
<li>Strongly,</li>
<li>Dynamically,</li>
<li>Implicitly</li>
</ul>
<p>typed.</p>
</td></tr></table>
<!-- end right -->
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->
<h1 id="testimonial">Testimonial</h1>
<blockquote>
<p>I’ve been a statically typed bigot for quite a few years.
I learned my lesson the hard way while using C.
Too many systems crashed in the field due to silly typing errors. […]</p>
</blockquote>
<blockquote>
<p>Four years ago I got involved with Extreme Programming. […] I can’t
imagine not having a comprehensive suite of unit tests to back up
my development. […]</p>
</blockquote>
<blockquote>
<p>About two years ago I noticed something.
I was depending less and less on the type system for safety.
My unit tests were preventing me from making type errors. […]</p>
</blockquote>
<blockquote>
<p>So I tried writing some applications in Python, and then Ruby.
I was not entirely surprised when I found that type issues simply
never arose.</p>
</blockquote>
<p>– <a href="http://www.artima.com/weblogs/viewpost.jsp?thread=4639">Bob Martin</a></p>
</div>
<div class='slide '>
<!-- _S9SLIDE_ -->