<?php
$🍞 = "bread";
echo "Some delicious " . $🍞;

I mean, there's no reason why it shouldn't work. An emoji is just a Unicode character (OK, not just a character - but we'll get on to that), so it should be fine to use anywhere.

Emoji work perfectly well as function names:

function 😺🐶() {
   echo "catdog!";
}
😺🐶();

Definitions:

define( "❓", "huh?" );
echo ❓;

And, well, pretty much everywhere:

class 🦜
{
    public int $🐦;
    public ?string $🦃;

    public function __construct(int $🐦, ?string $🦃)
    {
        $this->🐦 = $🐦;
        $this->🦃 = $🦃;
    }
}
$🐓 = new 🦜(1234, "birb");
echo $🐓->🐦;

How about namespaces? Yup!

namespace 😜;
class 😉 {
    public function 😘() {
        echo "Wink!";
    }
}

use 😜\😉;
$😊 = new 😉();
$😊->😘();

Even moderately complex Unicode sequences work:

echo <<<🏳️‍🌈
Unicode is magic!
🏳️‍🌈;

I've written before about the Quirks and Limitations of Emoji Flags. The humble 🏳️‍🌈 is actually the sequence U+1F3F3 (white flag), U+FE0F (Variation Selector 16), U+200D (Zero Width Joiner), U+1F308 (Rainbow).

Take a complex emoji like "Female Astronaut with Medium Dark Skin Tone" - 🧑🏾‍🚀 - that also works!

$🧑🏾‍🚀 = 1;
$👷🏻‍♂️ = 2;
echo $🧑🏾‍🚀 + $👷🏻‍♂️;

Probable the most complex emoji has 10 different codepoints! It looks like this - 🧑🏾‍❤️‍💋‍🧑🏻

And it works!

$🧑🏾‍❤️‍💋‍🧑🏻 = "Kiss Kiss. Bang Bang!";
echo $🧑🏾‍❤️‍💋‍🧑🏻[-1];

There are some emoji which don't work;

$5️⃣ = "five";

The 5️⃣ emoji is U+0035 (Digit Five), U+FE0F (Variation Selector 16), U+20E3 (Combining Enclosing Keycap). PHP doesn't allow variables to start with digits, so it craps out with PHP Parse error: syntax error, unexpected integer "5", expecting variable or "{" or "$" in php shell code on line 1

You also can't use "punctuation" emoji as though they were normal characters:

echo 5 ❗= 6;

And, while not strictly emoji, you can't use mathematical symbols:

echo 5 ≤ 6;

So, there you have it. Is this useful? Well, probably. It is easy to get lost in a sea of text - so little pictograms can make it easier to see what you're doing. If the basic ASCII characters aren't part of your native language, perhaps it is useful to make use of the full range of Unicode.

Does your favourite programming language support Emoji?