What are php variable parameters?

Look at a piece of code first

function concatenate($transform, ...$strings) {
	$string = '';
	foreach($strings as $piece) {
		$string .= $piece;
	}
	return($transform($string));
}

echo concatenate("strtoupper", "I'd ", "like ",
	4 + 2, " apples");

When the function is defined, use... Operator to indicate that this is a variable parameter, if you pass If 2 or more parameters are provided, these parameters will be added to this array.

Argument Unpacking
This is a function that echoes the above function.

Variadic functions allow you to declare the incoming parameter array, and parameter unpacking allows you to pass an array to a function and automatically unpack it inside the function. The example is as follows:

$email[] = "Hi there";
$email[] = "Thanks for registering, hope you like it";

mail("someone@example.com", ...$email);

You can put Put all the parameters in an array, and PHP will handle it all for you :)

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