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    <p>Here is an example of <em>using</em> a TryXxx method:</p> <pre><code>string s = Console.ReadLine(); int x; if (int.TryParse(s, out x)) { Console.WriteLine("You entered the valid integer {0}", x); } else { Console.WriteLine("Invalid input!"); } </code></pre> <p>Here is an example of <em>defining</em> the method:</p> <pre><code>bool TryParse(string s, out int x) // out parameter for result { if (!allCharactersAreValid(s)) { x = 0; return false; } // More checks... // Parse the string... x = 42; return true; } </code></pre> <p><strong>Exception handling</strong></p> <blockquote> <p>Most specificly what to do with rised exceptions in custom 'try' pattern methods</p> </blockquote> <p>Your method probably should avoid throwing any exceptions - if your user wanted exceptions they would use the non-Try version. You should therefore try to avoid calling methods which can throw when implementing your TryXxx. However some exceptions are unavoidable and could be thrown out of your control - for example <code>OutOfMemoryException</code>, <code>StackOverflowException</code>, etc... There is nothing you can do about this and you should not try to catch these exceptions, just let them propagate to the caller. Don't swallow them, don't log them - that's the caller's responsibility.</p> <p>An example of this is <code>Dictionary&lt;TKey, TValue&gt;.TryGetValue</code> when the key object provided to this method throws an exception when <code>GetHashCode</code> is called. Then the resulting exception is <em>not</em> caught inside the <code>TryGetValue</code> method - the caller will see the exception. This code demonstrates this happening:</p> <pre><code>using System; using System.Collections.Generic; class Foo { public override int GetHashCode() { throw new NotImplementedException(); } } class Program { public static void Main() { Dictionary&lt;object, object&gt; d = new Dictionary&lt;object, object&gt;(); d["bar"] = 42; object s; Foo foo = new Foo(); if (d.TryGetValue(foo, out s)) // results in NotImplementedException { Console.WriteLine("found"); } } } </code></pre>
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    1. USMark Byers
    1. USMark Byers
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    1. COthank you, but Im looking for implementation of this pattern. How to create methods like TryParse().
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      1. USkofucii
    2. COIndeed, too many developers assume that the `Try`-* methods are just wrappers for exception handling. That always bugs me.
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      1. USDan Tao
 

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