PHP - Make 'new' of a Class and Arguments set in a string - php

Question

I've a Class and Arguments set in a variable like this:
$myVar = '\Api\MyClass(\DateTimeInterface::RFC3339_EXTENDED)';
I need to make a new of this variable.
I tried multiple solutions and at the end the new of the Class was solved but I cannot pass the argument.
My code is:
<?php
$myVar = '\Api\MyClass(\DateTimeInterface::RFC3339_EXTENDED)';
$className = substr($myVar, 0, strpos($myVar, "(")); // $className will be: \Api\MyClass
if (class_exists($className)) {
preg_match('/\((.*?)\)/', $myVar, $classArguments); $classArguments will be: \DateTimeInterface::RFC3339_EXTENDED
$obj = new $className($classArguments[1]); // it doesn't work
}
the problem is that $classArguments[1] is passed as string to my class. Below the difference:
// It works
$p = \DateTimeInterface::RFC3339_EXTENDED;
var_dump($p);
// and return
string(15) "Y-m-d\TH:i:s.vP"
// It doesn't work
$p = "\DateTimeInterface::RFC3339_EXTENDED";
var_dump($p);
// return
string(36) "\DateTimeInterface::RFC3339_EXTENDED"
can you help me?
Thank you.

Answer 1

New can only be used to create an instance. Make your constructor expecting that date format as default, so you are not required to pass it.
class MyClass {
public function __construct(string $dateFormat = DateTimeInterface::RFC3339_EXTENDED)
{
}
}
$var = 'MyClass';
$instance = new $var;
$p = "\DateTimeInterface::RFC3339_EXTENDED";
will not work, because that is now a string and not the constants value.
You also can pass something like so
class MyClass {
public function __construct(string $something = '')
{
echo $something;
}
}
$var = 'MyClass';
$text = 'Hello world';
$instance = new $var($text);
Hello world
If you need the complete string to be parsed try eval(), but not recommended.
$var = 'new MyClass("hello world");';
$instance = eval($var);
Hello world
or, but not recommended.
$var = 'MyClass("hello world")';
$instance = eval("new {$var};");
Hello world

Answer 2

You can use the constant function to get the value of a constant.
A simple example class that just outputs the parameter value when initialized.
class MyClass
{
function __construct($arg) {
echo "$arg\n";
}
}
new MyClass('anything'); // outputs "anything"
This is just a helper that gets the class name and argument string from a string like your $myVar.
function parseClassAndArgument(string $str): array {
preg_match('/(.*)\((.*)\)/', $str, $matches);
[, $className, $argument] = $matches;
return [$className, $argument];
}
This helper allows you to pass either a string value or a name of a constant, and guesses which one it is based on whether there is a :: in the string name. You can replace this with just the constant($argument) part if you know $myVar will always contain a constant name.
function parseArgValue(string $argument): string {
return strpos($argument, '::') ? constant($argument) : $argument;
}
This recognizes that $argument refers to a constant and outputs Y-m-d\TH:i:s.vP
$myVar = 'MyClass(\DateTimeInterface::RFC3339_EXTENDED)';
[$className, $argument] = parseClassAndArgument($myVar);
new $className(parseArgValue($argument));
This outputs the string foo as is.
$myVar = 'MyClass(foo)';
[$className, $argument] = parseClassAndArgument($myVar);
new $className(parseArgValue($argument));
This is a simplified example that only handles one parameter for the class constructor, but I hope it helps to get you along!