Is it legal to use double-quotes in string interpolation?

[Gert Jan Schoneveld <gertjan@xxxxxxxxxxxxxxxx>]

Dear all,

We have produced some php code that works fine when we run it but gives problems when we scan it using the xgettext command line tool (0.23 or higher). I reported this to them and the question now is: Is our code valid php?

The code runs fine with PHP 8.4.11 (cli) from The PHP Group. Does this mean it is valid php? Or is php similar to c++ with compiler dependent things and/or undefined behavior when doing some other things?

I found two things in the specification on https://phplang.org/spec/09-lexical-structure.html that may suggest that it is not valid what we are doing:

1. This sentence: "The literal can contain any source character except double-quote (") and backslash (\\), which can only be represented by their corresponding escape sequence."

2. The definition only talks about "property-in-string". In my second example we are not using a property but a method on an object.

I hope you can give me a definitive answer on whether this example is valid.

Example code:
<?php
class MyClass
{
  public function method(string $p)
  {
    return $p;
  }
}

$arr = [
    "key" => 123
];

$obj = new MyClass();

echo "Test {$arr["key"]}" . PHP_EOL;
echo "Test {$obj->method("456")}" . PHP_EOL;
echo gettext("Hello") . PHP_EOL;

Regards,

Gert Jan Schoneveld