src/Collection/ArrayCollection.php
public function join(?string $glue = null, ?callable $callback = null): string
    {
        return $this->implode($glue, $callback);
    }
public function join(?string $glue = null, ?callable $callback = null): string
    {
        return $this->implode($glue, $callback);
    }
public function join ( ? string $ glue = null , ? callable $ callback = null ) : string { return $ this -> implode ( $ glue , $ callback ) ; }
Alias for implode

Optional callback should return a string value for concatenation.

Callback signature:

<code>
function ($value, $key): string {}
</code>

@param string|null   $glue     The string to join around
@param callable|null $callback The callback function

@return string
Alias for implode