PHP function as parameter default

Question

Take the following function for example:

private function connect($method, $target = $this->_config->db()) {
    try {
        if (!($this->_pointer = @fopen($target, $method)))
            throw new Exception("Unable to connect to database");
    }  catch (Exception $e) {
            echo $e->getMessage();
    }
}

As you can see I inserted the function $this->_config->db() into the parameter $target as it's default value. I understand this is not the correct syntax and am just trying to explain my aim.

$this->_config->db() is a getter function.

Now I know I can use an anonymous function and call it via $target later, but I want $target to also accept direct string values.

How could I give it a default value of the whatever is returned by $this->_config->db() and still be able to overwrite it with a string value?

user268396 · Accepted Answer · 2012-01-05 10:16:34Z

7

Why not accept NULL values by default (test with is_null()) and if so call your default function?

answered Jan 5, 2012 at 10:16

user268396

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1 Comment

George Reith Over a year ago

This is what I used and the least obtrusive method provided, thanks. if(is_null($target)) $target = $this->_config->db();

DaveRandom · Accepted Answer · 2012-01-05 10:14:47Z

2

You can use is_callable() and is_string().

private function connect($method, $target = NULL) {
    if (is_callable($target)) {
        // We were passed a function
        $stringToUse = $target();
    } else if (is_string($target)) {
        // We were passed a string
        $stringToUse = $target;
    } else if ($target === NULL) {
        // We were passed nothing
        $stringToUse = $this->_config->db();
    } else {
        // We were passed something that cannot be used
        echo "Invalid database target argument";
        return;
    }
    try {
        if (!($this->_pointer = @fopen($stringToUse, $method)))
            throw new Exception("Unable to connect to database");
    }  catch (Exception $e) {
            echo $e->getMessage();
    }
}

answered Jan 5, 2012 at 10:14

DaveRandom

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2 Comments

user268396 Over a year ago

But the OP want's to call a specific method by default rather than accept arbitrary callable's?

DaveRandom Over a year ago

Well, you can just remove the first section of the elseif tree then. This version still does that, it just gives the extra option of passing a function.

Fenton · Accepted Answer · 2012-01-05 10:13:29Z

1

I would perform a check to see if a value was passed and call my function in a simple check inside the method:

private function connect($method, $target = '') {
    try {
        if ($target === '') {
            $target = $this->_config->db()
        }

        if (!($this->_pointer = @fopen($target, $method))) {
            throw new Exception("Unable to connect to database");
        }
    } catch (Exception $e) {
        echo $e->getMessage();
    }
}

answered Jan 5, 2012 at 10:13

Fenton

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1 Comment

TheFrost Over a year ago

Everywhere else I find "null" as default value and you used empty string. May I ask why? Is it because you want it to be in the same type (string) as the custom value might be? Any reason in PHP to do that? I'm just curious.

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