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| <h1>Functions </h1> |
| |
| |
| |
| <p>Functions play an important role in Mita. |
| They give the language a modern feel through features that go beyond what C has to offer, such as <a href="#polymorphism">polymorphism</a> and <a href="#extension-methods">extension methods</a>.</p> |
| |
| <p>You have already seen the <code>fn</code> keyword, which allows you to declare new functions. Alternatively you can use <code>function</code> instead of <code>fn</code> if that suits your style better. |
| By convention in Mita functions are named in <code>camel case</code> style. In <code>camel case</code>, words are separated by capital letters and for functions we start with a lower-case one. |
| Here is an example that contains function definitions:</p> |
| <div class="highlight"><pre class="chroma"><code class="language-TypeScript" data-lang="TypeScript"><span class="nx">fn</span> <span class="nx">helloWorld() {</span> |
| <span class="k">return</span> <span class="s2">"hello world"</span><span class="p">;</span> |
| <span class="p">}</span> |
| |
| <span class="kd">function</span> <span class="nx">addOne</span><span class="p">(</span><span class="nx">x</span> : <span class="kt">int32</span><span class="p">)</span> <span class="o">:</span> <span class="nx">int32</span> <span class="p">{</span> |
| <span class="k">return</span> <span class="nx">x</span> <span class="o">+</span> <span class="mi">1</span><span class="p">;</span> |
| <span class="p">}</span></code></pre></div> |
| <h2 id="return-values">Return Values</h2> |
| |
| <p>All functions have a return type. If a function does not return any value, its type is <code>void</code>. |
| If you don’t explicitly specify a return type, the compiler will infer the common type of all <code>return</code> statements.</p> |
| <div class="highlight"><pre class="chroma"><code class="language-TypeScript" data-lang="TypeScript"><span class="c1">// The compiler will infer bool as return type |
| </span><span class="c1"></span><span class="nx">fn</span> <span class="nx">isEvent</span><span class="p">(</span><span class="nx">x</span> : <span class="kt">int32</span><span class="p">)</span> <span class="p">{</span> |
| <span class="k">if</span><span class="p">(</span><span class="nx">x</span> <span class="o">%</span> <span class="mi">2</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span> <span class="p">{</span> |
| <span class="k">return</span> <span class="kc">true</span><span class="p">;</span> |
| <span class="p">}</span> <span class="k">else</span> <span class="p">{</span> |
| <span class="k">return</span> <span class="kc">false</span><span class="p">;</span> |
| <span class="p">}</span> |
| <span class="p">}</span> |
| |
| <span class="nx">fn</span> <span class="nx">giveAnotherOne</span><span class="p">()</span> <span class="o">:</span> <span class="nx">uint32</span> <span class="p">{</span> |
| <span class="k">return</span> <span class="mi">1</span><span class="p">;</span> |
| <span class="p">}</span></code></pre></div> |
| <h2 id="polymorphism">Polymorphism</h2> |
| |
| <p>Functions can share the same name as long as the types of their parameters differ. |
| This concept is referred to as <code>polymorphism</code> and is useful to enable different behavior depending on the type of input. |
| Suppose you wanted to serialize structures to JSON messages. Because of polymorphism you can write the following code:</p> |
| <div class="highlight"><pre class="chroma"><code class="language-TypeScript" data-lang="TypeScript"><span class="kr">package</span> <span class="nx">main</span><span class="p">;</span> |
| <span class="kr">import</span> <span class="nx">platforms</span><span class="p">.</span><span class="nx">xdk110</span><span class="p">;</span> |
| |
| <span class="nx">struct</span> <span class="nx">AccelData</span> <span class="p">{</span> |
| <span class="kd">var</span> <span class="nx">x</span> : <span class="kt">int32</span><span class="p">;</span> |
| <span class="kd">var</span> <span class="nx">y</span> : <span class="kt">int32</span><span class="p">;</span> |
| <span class="p">}</span> |
| <span class="nx">struct</span> <span class="nx">EnvData</span> <span class="p">{</span> |
| <span class="kd">var</span> <span class="nx">temp</span> : <span class="kt">int32</span><span class="p">;</span> |
| <span class="p">}</span> |
| |
| <span class="nx">fn</span> <span class="nx">toJSON</span><span class="p">(</span><span class="nx">data</span> : <span class="kt">AccelData</span><span class="p">)</span> <span class="p">{</span> |
| <span class="k">return</span> <span class="sb">`{ "x": </span><span class="si">${</span><span class="nx">data</span><span class="p">.</span><span class="nx">x</span><span class="si">}</span><span class="sb">, "y": </span><span class="si">${</span><span class="nx">data</span><span class="p">.</span><span class="nx">y</span><span class="si">}</span><span class="sb"> }`</span><span class="p">;</span> |
| <span class="p">}</span> |
| <span class="nx">fn</span> <span class="nx">toJSON</span><span class="p">(</span><span class="nx">data</span> : <span class="kt">EnvData</span><span class="p">)</span> <span class="p">{</span> |
| <span class="k">return</span> <span class="sb">`{ "temp": </span><span class="si">${</span><span class="nx">data</span><span class="p">.</span><span class="nx">temp</span><span class="si">}</span><span class="sb"> }`</span><span class="p">;</span> |
| <span class="p">}</span> |
| |
| <span class="nx">every</span> <span class="mi">1</span> <span class="nx">second</span> <span class="p">{</span> |
| <span class="kd">let</span> <span class="nx">environmentalState</span> <span class="o">=</span> <span class="nx">EnvData</span><span class="p">(</span><span class="nx">temp</span> <span class="o">=</span> <span class="nx">environment</span><span class="p">.</span><span class="nx">temperature</span><span class="p">.</span><span class="nx">read</span><span class="p">());</span> |
| <span class="nx">println</span><span class="p">(</span><span class="nx">toJSON</span><span class="p">(</span><span class="nx">environmentalState</span><span class="p">));</span> |
| <span class="p">}</span></code></pre></div> |
| <p>Notice how we have two functions called <code>toJSON</code>. Depending on the type of the parameter they are called with, the compiler chooses |
| one or the other function.</p> |
| |
| <h2 id="extension-methods">Extension Methods</h2> |
| |
| <p>In the example above we called the <code>toJSON</code> function how you would expect a function call to look like: <code>toJSON(environmentalState)</code>. |
| Mita offers another style of calling functions which we refer to as <em>extension methods</em>: <code>environmentalState.toJSON()</code>. |
| With this style you can write the first argument of the function on the left side and call the function “on that expression”. |
| This gives the expression an object oriented look and feel, even though it is still just a plain old function call.</p> |
| |
| <p>Extension methods are very powerful when they are combined with polymorphism. |
| Considering the example above we could write code that looks very object oriented, but without incurring its complexity:</p> |
| <div class="highlight"><pre class="chroma"><code class="language-TypeScript" data-lang="TypeScript"><span class="nx">fn</span> <span class="nx">printState</span><span class="p">(</span><span class="nx">accel</span> : <span class="kt">AccelData</span><span class="p">,</span> <span class="nx">env</span> : <span class="kt">EnvData</span><span class="p">)</span> <span class="p">{</span> |
| <span class="nx">println</span><span class="p">(</span><span class="nx">accel</span><span class="p">.</span><span class="nx">toJSON</span><span class="p">());</span> |
| <span class="nx">println</span><span class="p">(</span><span class="nx">env</span><span class="p">.</span><span class="nx">toJSON</span><span class="p">());</span> |
| <span class="p">}</span></code></pre></div> |
| <p>Calling functions this way is not unique to Mita. |
| <em>Go</em> supports a very similar concept (receivers), <em>C#</em> supports an extension method concept and <em>Xtend</em> even has the exact same concept.</p> |
| |
| <h2 id="named-parameters">Named Parameters</h2> |
| |
| <p>When invoking functions the parameters can be specified by position or name. The style of invocation must not be mixed. There are no optional parameters.</p> |
| <div class="highlight"><pre class="chroma"><code class="language-TypeScript" data-lang="TypeScript"><span class="nx">foo</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">);</span> |
| <span class="nx">foo</span><span class="p">(</span><span class="nx">x</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="nx">y</span><span class="o">=</span><span class="mi">2</span><span class="p">);</span> |
| <span class="nx">foo</span><span class="p">(</span><span class="nx">x</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="nx">x</span><span class="o">=</span><span class="mi">2</span><span class="p">);</span> <span class="cm">/* compile error: parameter x has already been specified */</span> |
| <span class="nx">foo</span><span class="p">(</span><span class="nx">x</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">);</span> <span class="cm">/* compile error: mixed positional and named parameters */</span> |
| <span class="nx">foo</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="nx">y</span><span class="o">=</span><span class="mi">2</span><span class="p">);</span> <span class="cm">/* compile error: mixed positional and named parameters */</span></code></pre></div> |
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