Include constant in string without concatenating

Is there a way in PHP to include a constant in a string without concatenating?

define('MY_CONSTANT', 42);

echo "This is my constant: MY_CONSTANT";

No.

With Strings, there is no way for PHP to tell string data apart from constant identifiers. This goes for any of the string formats in PHP, including heredoc.

constant() is an alternative way to get hold of a constant, but a function call can't be put into a string without concatenation either.

Manual on constants in PHP

Yes it is (in some way ;) ):

define('FOO', 'bar');

$test_string = sprintf('This is a %s test string', FOO);

This is probably not what you were aiming for, but I think, technically this is not concatenation but a substitution and from this assumption, it includes a constant in a string without concatenating.

To use constants inside strings you can use the following method:

define( 'ANIMAL', 'turtles' ); 
$constant = 'constant';

echo "I like {$constant('ANIMAL')}";

How does this work?

You can use any string function name and arbitrary parameters

One can place any function name in a variable and call it with parameters inside a double-quoted string. Works with multiple parameters too.

$fn = 'substr';

echo "I like {$fn('turtles!', 0, -1)}";

Produces

I like turtles

Anonymous functions too

You can also use anonymous functions provided you're running PHP 5.3+.

$escape   = function ( $string ) {
    return htmlspecialchars( (string) $string, ENT_QUOTES, 'utf-8' );
};
$userText = "<script>alert('xss')</script>";
echo( "You entered {$escape( $userText )}" );

Produces properly escaped html as expected.

Callback arrays not allowed!

If by now you are under the impression that the function name can be any callable, that's not the case, as an array that returns true when passed to is_callable would cause a fatal error when used inside a string:

class Arr
{

    public static function get( $array, $key, $default = null )
    {
        return is_array( $array ) && array_key_exists( $key, $array ) 
            ? $array[$key] 
            : $default;
    }
}

$fn = array( 'Arr', 'get' );
var_dump( is_callable( $fn ) ); // outputs TRUE

// following line throws Fatal error "Function name must be a string"
echo( "asd {$fn( array( 1 ), 0 )}" ); 

Keep in mind

This practice is ill-advised, but sometimes results in much more readable code, so it's up to you - the possibility is there.

define( 'FOO', 'bar');  
$FOO = FOO;  
$string = "I am too lazy to concatenate $FOO in my string";