How Can I Call PHP Functions Within HEREDOC Strings?

Invoking PHP Functions in HEREDOC Strings: A Detailed Analysis

HEREDOC strings provide a convenient way to represent multiline blocks of text in PHP. While they support variable substitution using the '$' prefix, accessing more complex expressions, such as array elements, requires the use of braces '{}'.

In PHP 5, it became possible to invoke functions within braces in HEREDOC strings. However, this requires a nuanced approach. The function name must be stored in a variable, and the invocation must emulate a dynamically named function. For example:

$fn = 'testfunction';
function testfunction() { return 'ok'; }
$string = <<<heredoc
plain text and now a function: {$fn()}
heredoc;

This approach can appear cumbersome compared to the direct function invocation syntax:

$string = <<<heredoc
plain text and now a function: {testfunction()}
heredoc;

Alternative solutions exist, such as breaking out of the HEREDOC to call the function or reversing the approach by integrating PHP code into HTML, as shown in the code example provided in the question. However, these methods have their limitations.

A Simpler Solution

If a more straightforward solution is desired, a simplified approach can be employed:

function fn($data) {
  return $data;
}
$fn = 'fn';

$my_string = <<<EOT
Number of seconds since the Unix Epoch: {$fn(time())}
EOT;

This approach offers a less convoluted alternative while maintaining the functionality of invoking functions within HEREDOC strings.

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