How can I access a deep object property named as a variable (dot notation) in php?

Question

There are many questions similar to this, however this is slightly different since it's about deep object property access, not just one level of depth.

Let's say I have a variable containing the string foo.bar.

$user = new User();
$user->foo = new Foo();
$user->foo->bar = "Hello World";

$variable = "foo.bar"

I would like to echo $user->foo->bar by making use of $variable:

echo $user->foo->bar

This is what I have tried so far but with no success (it says NULL):

$value = str_replace(".", "->", $value);
echo $user->{$value};

Answer 1

It is very easy to reduce the object path using variable property notation ($o->$p):

$path = 'foo.bar';
echo array_reduce(explode('.', $path), function ($o, $p) { return $o->$p; }, $user);

This could easily be turned into a small helper function.

Answer 2

A little improvement added to @deceze post.

This allow handling cases where you need to go through arrays also.

$path = 'foo.bar.songs.0.title';
echo array_reduce(explode('.', $path), function ($o, $p) { return is_numeric($p) ? $o[$p] : $o->$p; }, $user);

Edit:

And if you have PHP 7+, then the following will safely return null if a property's name is mistyped or if it doesn't exist.

$path = 'foo.bar.songs.0FOOBAR.title';
echo array_reduce(explode('.', $path), function ($o, $p) { return is_numeric($p) ? ($o[$p] ?? null) : ($o->$p ?? null); }, $user);