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src/site/articles/idiomatic-dart/index.html

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 layout: default
 title: "Idiomatic Dart"
 rel:
   author: bob-nystrom
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 <section>
 <h1>Idiomatic Dart</h1>
 <p>
@@ skipping 240 matching lines @@
 <h2 id="top-level-definitions">Top-level definitions</h2>
 
 <p>Dart is a "pure" object-oriented language in that everything you can place in a variable is a real object (no mutant "primitives") and every object is an instance of some class. It's not a <em>dogmatic</em> OOP language though. You aren't required to place everything you define inside some class. Instead, you are free to define functions, variables, and even getters and setters at the top level if you want.</p>
 
 {% highlight dart %}
 num abs(num value) => value < 0 ? -value : value;
 
 final TWO_PI = Math.PI * 2.0;
 
 int get today() {
-  final date = new DateTime.now();
+  final date = new Date.now();
   return date.day;
 }
 {% endhighlight dart 0 %}
 
 <p>Even in languages that don't require you to place everything inside a class or object, like JavaScript, it's still common to do so as a form of namespacing: top-level definitions with the same name could inadvertently collide. To address that, Dart has a library system that allows you to import definitions from other libraries with a prefix applied to disambiguate it. That means you shouldn't <em>need</em> to defensively squirrel your definitions inside classes.</p>
 
 <p>We're still exploring what this actually means for how we define libraries. Most of our code does place definitions inside classes, like Math. It's hard to tell if this is just an ingrained habit we have from other languages or a practice that's also good for Dart. This is an area we want feedback on.</p>
 
 <p>We do have some examples where we use top-level definitions. The first you'll run into is <code>main()</code> which is expected to be defined at the top level. If you work with the DOM, the familiar <code>document</code> and <code>window</code> "variables" are actually top-level getters in Dart.</p>
 
 <h2 id="strings-and-interpolation">Strings and interpolation</h2>
 
 <p>Dart has a few kinds of string literals. You can use single or double quotes, and you can use triple-quoted multiline strings:</p>
 
 {% highlight dart %}
 'I am a "string"'
 "I'm one too"
 
 '''I'm
 on multiple lines
 '''
 
 """
 As
 am
 I
 """
 {% endhighlight dart 0 %}
 
-<p>To build bigger strings from these pieces, you <em>can</em> just concatenate them using <code>+</code>:
+<p>There is no plus (+) operator on String. It's cleaner and faster to use <em>string interpolation</em>:</p>
 
 {% highlight dart %}
 var name = 'Fred';
-var salutation = 'Hi';
-var greeting = salutation + ', ' + name;
-{% endhighlight dart 0 %}
-
-<p>But it's cleaner and faster to use <em>string interpolation</em>:</p>
-
-{% highlight dart %}
-var name = 'Fred';
 var salutation = 'Hi';
 var greeting = '$salutation, $name';
 {% endhighlight dart 0 %}
 
-<p>A dollar sign (<code>$</code>) in a string literal followed by a variable will expand to that variable's value. (If the variable isn't a string, it calls <code>toString()</code> on it.) You can also interpolate expressions by placing them inside curly braces:</p>
+<p>A dollar sign (<code>$</code>) in a string literal followed by a variable
+  will expand to that variable's value. (If the variable isn't a string,
+  it calls <code>toString()</code> on it.) You can also interpolate expressions by
+  placing them inside curly braces:</p>
 
 {% highlight dart %}
 var r = 2;
 print('The area of a circle with radius $r is ${Math.PI * r * r}');
 {% endhighlight dart 0 %}
 
 <h2 id="operators">Operators</h2>
 
 <p>Dart shares the same operators and precedences that you're familiar with from C, Java, etc. They will do what you expect. Under the hood, though, they are a little special. In Dart, an expression using an operator like <code>1 + 2</code> is really just syntactic sugar for calling a method. The previous example looks more like <code>1.+(2)</code> to the language.</p>
 
@@ skipping 42 matching lines @@
   <li>Any number, including floating points.</li>
 </ol>
 
 <p>Using <code>int</code> handles the first set, and using <code>num</code> handles the second set. It's very rare that we want a number that <i>must</i> have
 a floating point and <i>cannot</i> be an integer, which is what double expresses.</p>
 
 <p>Idiomatic Dart numbers are annotated with either <code>int</code> or <code>num</code>, rarely <code>double</code>.</p>
 
 </section>