When Should I Use Curly Braces in PHP String Literals?

Curly Braces in String Literals in PHP

Curly braces ({ }) in string literals in PHP signify complex (curly) syntax for string interpolation. This syntax enables the inclusion of complex expressions within strings.

In this syntax, any scalar variable, array element, or object property with a string representation can be inserted. To do so, simply replicate the expression as it would appear outside the string and enclose it in { and }.

For example:

$great = 'fantastic';

// Output: This is fantastic
echo "This is {$great}";

// Output: This is 500 centimeters broad
echo "This square is {$square->width}00 centimeters broad.";

// Output: This works: John Doe
echo "This works: {$arr['key']}";

However, it's important to note that curly braces are not always necessary. For simple string concatenation, using double quotes is sufficient. For instance:

$a = 'abcd';

// Output: abcd abcd
$out = "$a $a"; // Same as
$out = "{$a} {$a}";

Curly braces become essential when the string contains undefined variables or complex expressions that would otherwise result in errors or unexpected behavior. For instance:

$out = "$aefgh"; // Error or unexpected result

// Solution:
$out = "${a}efgh"; // or
$out = "{$a}efgh";

By using curly braces, PHP interprets these expressions correctly and includes their respective values within the string.

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