including $book->author in echo ""
===

I'm trying to print $book->author in an echo statement. Right now I'm using concatenation. 

    echo "book author: " . $book->author . "<br />";

How can I include the whole thing in double quotes? If I do the following, it assumes I'm trying to echo the `$book` object and that `->author` is a regular string.

    echo "book author: $book->author<br />";

