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POValidating constructor parameters, making sure parameters have the correct type
 

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    <p>Writing my first PHP Class and came across an issue, the following is my <code>__construct</code> method:</p> <pre><code>public function __construct($foo,$bar) { $this-&gt;foo = $foo; $this-&gt;bar = $bar; } </code></pre> <p>Both <code>$foo</code> and <code>$bar</code> are required, without them, the methods will not work. It's OK when they aren't defined when the object is instantiated like so:</p> <pre><code>$var = new Class(); </code></pre> <p>As this throws an exception (e.g. Class requires 2 params, none set). But if they are set but not of the correct type like so:</p> <pre><code>$var = new Class('33','ddd'); </code></pre> <p>My methods will fail as the variables have the wrong type.</p> <p><strong>Where should I be validating these? In the constructor or in each method?</strong></p> <p>My solution that I'm using right now works, but I'm not sure if it's the right way:</p> <pre><code>// $foo needs to be a string with letters only // $bar needs to be an integer public function __construct($foo,$bar) { $this-&gt;foo = $foo; $this-&gt;bar = $bar; if(!is_numeric($bar)){ // Throw exception } elseif(other validation case) etc... } </code></pre> <p>The concepts of OO programming are pretty new to me, so links to any reference material you have would be greatly appreciated.</p>
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    1. COYou shouldn't "print error message" in a constructor, you should throw an exception (like in @Gordon's answer below). The constructor's purpose is to have a valid object after it's been invoked. By simply printing an error message instead of an exception, you will most likely end up with an invalid object that will screw up your whole program.
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      1. USnetcoder
    2. CONope, you shouldn't use exceptions. Use `assert()` to check variable types. Invalid arguments are foremost an development problem. This is were you want to catch such problems. Exceptions should be used when invalid arguments are to be expected at runtime, and if you can reasonably implement catch logic to retry with alternate arguments. E.g. [Assert vs Exceptions](http://stackoverflow.com/questions/117171/design-by-contract-tests-by-assert-or-by-exception/117247#117247) but also see duplicates..
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    3. CO@mario: I agree that `assert` can be used to check types internally. But not in a constructor. A bad argument passed to a constructor and it is an exception, an exception being an exceptional situation where the program cannot continue further. If a constructor has bad arguments passed to it, then it shouldn't continue further. Otherwise, like I said, you end up with an invalid object and a functioning program that takes the object as valid, and keep going until some major screw-up happens (garbage being inserted repeatedly in your DB per example).
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