Include constant in string without concatenating

Question

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";

define('FOO', 'bar');
$constants = create_function('$a', 'return $a;');
echo "Hello, my name is {$constants(FOO)}";

If you really want to echo constant without concatenation here is solution:

define('MY_CONST', 300);
echo 'here: ', MY_CONST, ' is a number';

note: in this example echo takes a number of parameters (look at the commas), so it isn't real concatenation

Echo behaves as a function, it takes more parameters, it is more efficient than concatenation, because it doesn't have to concatenate and then echo, it just echoes everything without the need of creating new String concatenated object :))

EDIT

Also if you consider concatenating strings, passings strings as parameters or writing whole strings with " , The , (comma version) is always fastest, next goes . (concatenation with ' single quotes) and the slowest string building method is using double quotes ", because expressions written this way have to be evaluated against declared variables and functions..