Interpolate a constant (not variable) into 'heredoc'

Question

Consider:

The value of my_const is {my_const}.

MYECHO;
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Answer 1

Here is an little trick to allow double-quoted strings and heredocs to contain arbitrary expressions in curly braces syntax, including constants and other function calls. It uses the fact that a function name can be assigned to a variable and then called within heredoc:

= 5.3
    // Use a closure (anomynous function) like so:
    $_ = function ($val){return $val;};

    // Our test values
    define('abc', 'def');
    define('ghi', 3);

    $a = 1;
    $b = 2;

    function add($a, $b) { return $a+$b; }

    // Usage
    echo "b4 {$_(1+2)} after\n"; // Outputs 'b4 3 after'
    echo "b4 {$_(abc)} after\n"; // Outputs 'b4 def after'
    echo "b4 {$_(add($a, $b)+ghi*2)} after\n"; // Outputs 'b4 9 after'
    $text = <<