What Does ${ } Mean in PHP Syntax

What does ${ } mean in PHP syntax?

${ } (dollar sign curly bracket) is known as Simple syntax.

It provides a way to embed a variable, an array value, or an object
property in a string with a minimum of effort.

If a dollar sign ($) is encountered, the parser will greedily take as
many tokens as possible to form a valid variable name. Enclose the
variable name in curly braces to explicitly specify the end of the
name.

<?php
$juice = "apple";

echo "He drank some $juice juice.".PHP_EOL;
// Invalid. "s" is a valid character for a variable name, but the variable is $juice.
echo "He drank some juice made of $juices.";
// Valid. Explicitly specify the end of the variable name by enclosing it in braces:
echo "He drank some juice made of ${juice}s.";
?>

The above example will output:

He drank some apple juice.
He drank some juice made of .
He drank some juice made of apples.

Reference — What does this symbol mean in PHP?

Incrementing / Decrementing Operators

++ increment operator

-- decrement operator

Example    Name              Effect
---------------------------------------------------------------------
++$a       Pre-increment     Increments $a by one, then returns $a.
$a++       Post-increment    Returns $a, then increments $a by one.
--$a       Pre-decrement     Decrements $a by one, then returns $a.
$a--       Post-decrement    Returns $a, then decrements $a by one.

These can go before or after the variable.

If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.

For example:

$apples = 10;
for ($i = 0; $i < 10; ++$i) {
    echo 'I have ' . $apples-- . " apples. I just ate one.\n";
}

Live example

In the case above ++$i is used, since it is faster. $i++ would have the same results.

Pre-increment is a little bit faster because it really increments the variable and after that 'returns' the result. Post-increment creates a special variable, copies there the value of the first variable and only after the first variable is used, replaces its value with second's.

However, you must use $apples--, since first, you want to display the current number of apples, and then you want to subtract one from it.

You can also increment letters in PHP:

$i = "a";
while ($i < "c") {
    echo $i++;
}

Once z is reached aa is next, and so on.

Note that character variables can be incremented but not decremented and even so only plain ASCII characters (a-z and A-Z) are supported.

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Stack Overflow Posts:

• Understanding Incrementing

In PHP, what does the ${$ } syntax do?

Consider

$foo = 42;
$a = 'foo';
echo $$a; // Prints 42

That´s called a variable variable, since the variable´s name is determinated at runtime.
But is $$a[1] the same as ${$a[1]} or the same as {$$a}[1]? The brackets avoid that ambiguity, just like they do when dealing with operator precedence in math.

What does `${...}` that is not within a string mean in PHP?

This is covered in the documentation under the topic "Variable variables":

In order to use variable variables with arrays, you have to resolve an ambiguity problem. That is, if you write $$a[1] then the parser needs to know if you meant to use $a[1] as a variable, or if you wanted $$a as the variable and then the [1] index from that variable. The syntax for resolving this ambiguity is: ${$a[1]} for the first case and ${$a}[1] for the second.

So basically, you can use ${<expr>} to access a variable of the dynamic name <expr>, where <expr> can be any expression that returns a string. Alternatively, you could write:

$foo = "GLOBALS";
${$foo}["gasyarknd"] = "b";

// equivalent to:
$GLOBALS["gasyarknd"] = "b";

Of course, in the context of your question, ${"GLOBALS"} is not actually a variable variable, since "GLOBALS" is a static string, and not a variable. Semantically, it means the exact same thing as $GLOBALS.

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For more information, you can also have a look at the respective rule from PHP's grammar:

simple_variable:
        T_VARIABLE          { $$ = $1; }
    |   '$' '{' expr '}'    { $$ = $3; }
    |   '$' simple_variable { $$ = zend_ast_create(ZEND_AST_VAR, $2); }
;

The second part of the rule, '$' '{' expr '}', covers just this: ${, followed by any expression, followed by } is a completely valid way to access a variable in PHP. The third part of the rule covers "regular" variable variables, like $$foo.

What does the variable $this mean in PHP?

It's a reference to the current object, it's most commonly used in object oriented code.

• Reference: http://www.php.net/manual/en/language.oop5.basic.php
• Primer: http://www.phpro.org/tutorials/Object-Oriented-Programming-with-PHP.html

Example:

<?php
class Person {
    public $name;

    function __construct( $name ) {
        $this->name = $name;
    }
};

$jack = new Person('Jack');
echo $jack->name;

This stores the 'Jack' string as a property of the object created.

What's the difference between ${var} and {$var}

You are talking about Complex syntax. Looking into example shows that the meaning is same for both cases therefore it is up to you to decide which one to use based on your preferences.

When to wrap curly braces around a variable

What are PHP curly braces:

You know that a string can be specified in four different ways. Two of these ways are – double quote("") and heredoc syntax. You can define a variable in those 2 types of strings and PHP interpreter will parse or interpret that variable too, within the strings.

Now, there are two ways you can define a variable in a string – simple syntax which is the most used method of defining variables inside a string and complex syntax which uses curly braces to define variables.

Curly braces syntax:

To use a variable with curly braces is very easy. Just wrap the variable with { and } like:

{$variable_name}

Note: There must not be any gap between { and $. Else, PHP interpreter won't consider the string after $ as a variable.

Curly braces example:

<?php
$lang = "PHP";
echo "You are learning to use curly braces in {$lang}.";
?>

Output:

You are learning to use curly braces in PHP.

When to use curly braces:

When you are defining a variable inside a string, PHP might mix up the variable with other characters if using simple syntax to define a variable and this will produce an error. See the example below:

<?php
$var = "way";
echo "Two $vars to defining variable in a string.";
?>

Output:

Notice: Undefined variable: vars …

In the above example, PHP's interpreter considers $vars a variable, but, the variable is $var. To separate a variable name and the other characters inside a string, you can use curly braces. Now, see the above example using curly braces-

<?php
$var = "way";
echo "Two {$var}s to define a variable in a string.";
?>

Output:

Two ways to define a variable in a string.

Source: http://schoolsofweb.com/php-curly-braces-how-and-when-to-use-it/

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