CODEWITHSUNDEEP
phpvariables
AJD
AJD

Reputation: 434

Can I modify a variable within a string with another variable in PHP?

$pet ='dog'; 
$action='My '. $pet . 'likes to run.'; 
//The part I would like to modify
$pet ='cat'; 
//Modify the $pet variable inside the $action variable 
//after it has been defined.
echo $action;

This will output: My dog likes to run

Can I make it output: My cat likes to run

I also tried: 

$pet ='dog';  
$action=sprintf('My %s likes to run.', $pet);
$pet ='cat';
echo $action;

I do know that this could be achieved by creating a function with an argument like below. But I'm a php beginner and curious about the other methods.

function action($pet = "dog") {
    $p = 'My'. $pet . 'likes to run.';
    return $p;
}
$pet = 'cat';
echo action($pet);

Upvotes: 2

Views: 111

Answers (2)

Pieter van den Ham
Pieter van den Ham

Reputation: 4484

Well, I know that you probably weren't looking for this, but it is late and I am bored.

Disclaimer: this is a bad idea.

class MyString
{
    private $format, $pet;

    public function __construct($format, &$pet)
    {
        $this->format = $format;
        $this->pet = &$pet;
    }

    public function __toString()
    {
        return sprintf($this->format, $this->pet);
    }
}

$myString = new MyString('This is my little %s, cool huh?', $pet);

$pet = 'cat';
echo $myString."\n";

$pet = 'dog';
echo $myString."\n";

$pet = 'goldfish';
echo $myString."\n";

Output:

This is my little cat, cool huh?
This is my little dog, cool huh?
This is my little goldfish, cool huh?

Demo: https://3v4l.org/XmUEZ

Basically this class stores a reference to the $pet variable in it's fields. As such, when the $pet variable is updated, the reference in the class is updated as well.

Another one for good measure:

function mysprintf($format, &$variable)
{
    return function() use ($format, &$variable) {
        return sprintf($format, $variable);
    };
}

$print = mysprintf('This is my little %s, cool huh?', $pet);

$pet = 'cat';
echo $print()."\n";

$pet = 'dog';
echo $print()."\n";

$pet = 'goldfish';
echo $print()."\n";

https://3v4l.org/KJTKj

(Ab)uses closures to save the reference. Probably even worse.

Why is this a bad idea, you ask?

Consider solely this statement:

$pet = 'goldfish';

This is a simple assignment. Most programmers assume that this statement has no side-effects. That means that this statement changes nothing in the execution flow besides creating a new variable.

Our MyString or mysprintf violate this assumption. What should be a simple assignment, now has side-effects. It violates a programmer's expectation in the worst way possible.

Upvotes: 3

A l w a y s S u n n y
A l w a y s S u n n y

Reputation: 38502

You are trying to create a Dynamic String Variable, which is not possible in php for now. You can use the functional approach which you have implemented already :) .

function action($pet = "dog") {
    $p = 'My'. $pet . 'likes to run.';
    return $p;
}
$pet = 'cat';
echo action($pet);

if you use the below approach, unfortunately it will only covers printing part not when we need to reassign value of variable.

$pet ='dog';  
$action=sprintf('My %s likes to run.', $pet);
$pet ='cat';
echo $action;

So, just stick with the function way :)

Upvotes: 2

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