PHP curly string syntax question

I'm running PHP 5.3.0. I've found that the curly string syntax only works when the first character of the expression is $. Is there a way to include other types of expressions (function calls, etc)?

Trivial example:

<?php
$x = '05';
echo "{$x}"; // works as expected
echo "{intval($x)}"; // hoped for "5", got "{intval开发者_运维知识库(05)}"

<?php
$x = '05';
echo "{$x}";
$a = 'intval';
echo "{$a($x)}";
?>

No. Only variables of various forms can be substituted using variable substitution.

take a look at this link LINK

Example of the code,

Similarly, you can also have an array index or an object property parsed. With array indices, the closing square bracket (]) marks the end of the index. For object properties the same rules apply as to simple variables, though with object properties there doesn't exist a trick like the one with variables.

<?php
// These examples are specific to using arrays inside of strings.
// When outside of a string, always quote your array string keys 
// and do not use {braces} when outside of strings either.

// Let's show all errors
error_reporting(E_ALL);

$fruits = array('strawberry' => 'red', 'banana' => 'yellow');

// Works but note that this works differently outside string-quotes
echo "A banana is $fruits[banana].";

// Works
echo "A banana is {$fruits['banana']}.";

// Works but PHP looks for a constant named banana first
// as described below.
echo "A banana is {$fruits[banana]}.";

// Won't work, use braces.  This results in a parse error.
echo "A banana is $fruits['banana'].";

// Works
echo "A banana is " . $fruits['banana'] . ".";

// Works
echo "This square is $square->width meters broad.";

// Won't work. For a solution, see the complex syntax.
echo "This square is $square->width00 centimeters broad.";
?>

there are different things you can achieve with the curly brace, but it is limited, depending on how you use it.

<?php
class Foo
{
    public function __construct() {
        $this->{chr(8)} = "Hello World!";
    }
}

var_dump(new Foo());

Generally you don't need the braces around variables, unless you need to force PHP to treat something as a variable, where its normal parsing rules otherwise might not. The big one is multidimensional arrays. PHP's parser is non-greedy for deciding what's a variable and what isn't, so the braces are necessary to force PHP to see the rest of the array element references:

<?php

$arr = array(
    'a' => array(
         'b' => 'c'
    ), 
);

print("$arr[a][b]"); // outputs:  Array[b]
print("{$arr[a][b]}"); // outputs: (nothing), there's no constants 'a' or 'b' defined
print("{$arr['a']['b']}"); // ouputs: c