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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
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name="viewport"
content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no"
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<body>
<div class="reveal">
<div class="slides">
<section>
<h2>Call by value<br />vs.<br />Call by reference</h2>
<small>Marvin Borner</small>
</section>
<section>
<h2>Call by value</h2>
<p class="fragment">Der Standard in den meisten Sprachen</p>
<pre class="fragment">
<code class="c# hljs cs" data-trim data-line-numbers="1-11|8|1-4,9|10|1-11"><script type="text/template">
private static void ErhoeheZahl(int zahl)
{
zahl += 42;
}
static void Main(string[] args)
{
int bla = 0;
ErhoeheZahl(bla);
Console.WriteLine(bla);
}</script></code></pre>
<small
><code class="fragment console"
>[C#-Console] 0</code
></small
>
</section>
<section>
<h2>Call by reference</h2>
<p class="fragment">Wird meist bewusst verwendet</p>
<p class="fragment">
Kann in C# mit dem
<code style="color: #ffff55">ref</code> keyword
umgesetzt werden
</p>
<pre class="fragment">
<code class="c# hljs cs" data-trim data-line-numbers="1-11|8|1-4,9|10|1-11"><script type="text/template">
private static void ErhoeheZahl(ref int zahl)
{
zahl += 42;
}
static void Main(string[] args)
{
int bla = 0;
ErhoeheZahl(ref bla);
Console.WriteLine(bla);
}</script></code></pre>
<small
><code class="fragment console"
>[C#-Console] 42</code
></small
>
</section>
<section>
<h3>Besonderheiten - Objekte</h3>
<section>
<pre class="fragment">
<code class="c# hljs cs" data-trim data-line-numbers="1-12|9|1-5,10|11|1-12"><script type="text/template">
private static void FuegeHinzu(List<int> liste)
{
liste.Add(4);
liste.Add(5);
}
static void Main(string[] args)
{
List<int> liste = new List<int>() { 1, 2, 3 };
FuegeHinzu(liste);
Console.WriteLine(string.Join(", ", liste));
}</script></code>
</pre>
<small
><code class="fragment console"
>[C#-Console] 1, 2, 3, 4, 5</code
></small
>
</section>
<section>
<pre>
<code class="c# hljs cs" data-trim data-line-numbers="1-12|9|1-5,10|11|1-12"><script type="text/template">
private static void UeberschreibeListe(List<int> liste)
{
liste = new List<int>();
liste.Add(42);
}
static void Main(string[] args)
{
List<int> liste = new List<int>() { 1, 2, 3 };
FuegeHinzu(liste);
Console.WriteLine(string.Join(", ", liste));
}</script></code>
</pre>
<small
><code class="fragment console"
>[C#-Console] 1, 2, 3</code
></small
>
</section>
<section>
<pre>
<code class="c# hljs cs" data-trim data-line-numbers="1-12|9|1-5,10|11|1-12"><script type="text/template">
private static void UeberschreibeListe(ref List<int> liste)
{
liste = new List<int>();
liste.Add(42);
}
static void Main(string[] args)
{
List<int> liste = new List<int>() { 1, 2, 3 };
FuegeHinzu(ref liste);
Console.WriteLine(string.Join(", ", liste));
}</script></code>
</pre>
<small
><code class="fragment console"
>[C#-Console] 42</code
></small
>
</section>
</section>
<section>
<h3>Besonderheiten - Arrays</h3>
<section>
<pre>
<code class="c# hljs cs" data-trim data-line-numbers="1-11|8|1-4,9|10|1-11"><script type="text/template">
private static void BearbeiteFeld(int[] felder)
{
felder[0] = 42;
}
static void Main(string[] args)
{
int[] felder = new int[] { 1, 2, 3 };
BearbeiteFeld(felder);
Console.WriteLine(felder[0]);
}</script></code>
</pre>
<small
><code class="fragment console"
>[C#-Console] 42</code
></small
>
</section>
<section>
<pre>
<code class="c# hljs cs" data-trim data-line-numbers="1-11|8|1-4,9|10|1-11"><script type="text/template">
private static void UeberschreibeFelder(int[] felder)
{
felder = new int[] { 4, 5, 6 };
}
static void Main(string[] args)
{
int[] felder = new int[] { 1, 2, 3 };
UeberschreibeFelder(felder);
Console.WriteLine(felder[0]);
}</script></code>
</pre>
<small
><code class="fragment console"
>[C#-Console] 1</code
></small
>
</section>
<section>
<pre>
<code class="c# hljs cs" data-trim data-line-numbers="1-11|8|1-4,9|10|1-11"><script type="text/template">
private static void UeberschreibeFelder(ref int[] felder)
{
felder = new int[] { 4, 5, 6 };
}
static void Main(string[] args)
{
int[] felder = new int[] { 1, 2, 3 };
UeberschreibeFelder(ref felder);
Console.WriteLine(felder[0]);
}</script></code>
</pre>
<small
><code class="fragment console"
>[C#-Console] 4</code
></small
>
</section>
</section>
<section>
<h2>Mehrere Rückgabewerte</h2>
<pre>
<code class="c# hljs cs" data-trim data-line-numbers="1-13|10|1-6,11|12|1-13"><script type="text/template">
private static void Rueckgabe(ref int a, ref int b, ref int c)
{
a = 1;
b = 2;
c = 3;
}
static void Main(string[] args)
{
int a = 0, b = 0, c = 0;
Rueckgabe(ref a, ref b, ref c);
Console.WriteLine(a + ", " + b + ", " + c);
}</script></code>
</pre>
<small
><code class="fragment console"
>[C#-Console] 1, 2, 3</code
></small
>
</section>
<section>
<section>
<h2>Vorteile von call by reference</h2>
<ul>
<li class="fragment">
Muss nicht extra kopiert werden (weniger
Overhead)
</li>
<ul>
<li
style="list-style-type: none"
class="fragment"
>
→ schneller
</li>
</ul>
<li class="fragment">
Eine Funktion kann mehrere Rückgabewerte
besitzen
</li>
</ul>
</section>
<section>
<h2>Nachteile von call by reference</h2>
<ul>
<li class="fragment">
Teilweise nicht sehr lesbar/verständlich
</li>
<li class="fragment">
Probleme mit Garbage Collectors und
Multi-Threading
</li>
</ul>
</section>
</section>
<section>
<h2>Andere Sprachen</h2>
<section>
<h3>C</h3>
<pre class="fragment">
<code class="c hljs" data-trim data-line-numbers="1-11|8|1-4,9|10|1-11"><script type="text/template">
static void bearbeite_zeiger(int *zeiger)
{
*zeiger = 42;
}
void main(int argc, char **argv)
{
int zahl = 0;
bearbeite_zeiger(&zahl);
printf("%d\n", zahl);
}</script></code>
</pre>
<small
><code class="fragment console"
>[C-Console] 42</code
></small
>
</section>
<section>
<h3>JavaScript</h3>
<pre>
<code class="js hljs" data-trim data-line-numbers="1-11|9|1-3,10|5-7,11|1-11"><script type="text/template">
function ersetzen(obj) {
obj = {}; // Verändert das originale Objekt nicht
}
function bearbeiten(obj) {
obj.key = "Aaah"; // Verändert das originale Objekt
}
const toll = { key: "hihi" };
ersetzen(toll); // obj.key => "hihi"
bearbeiten(toll); // obj.key => "Aaah"
</script></code>
</pre>
</section>
</section>
<section>
<h2>
Danke, dass Sie so leise und aufmerksam waren. Tschüss!
</h2>
<small>Marvin Borner</small>
</section>
</div>
</div>
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