Calling PHP functions within HEREDOC strings

T

18

106

In PHP, the HEREDOC string declarations are really useful for outputting a block of html. You can have it parse in variables just by prefixing them with $, but for more complicated syntax (like $var[2][3]), you have to put your expression inside {} braces.

In PHP 5, it is possible to actually make function calls within {} braces inside a HEREDOC string, but you have to go through a bit of work. The function name itself has to be stored in a variable, and you have to call it like it is a dynamically-named function. For example:

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

As you can see, this is a bit more messy than just:

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

There are other ways besides the first code example, such as breaking out of the HEREDOC to call the function, or reversing the issue and doing something like:

?>
<!-- directly output html and only breaking into php for the function -->
plain text and now a function: <?PHP print testfunction(); ?>

The latter has the disadvantage that the output is directly put into the output stream (unless I'm using output buffering), which might not be what I want.

So, the essence of my question is: is there a more elegant way to approach this?

Edit based on responses: It certainly does seem like some kind of template engine would make my life much easier, but it would require me basically invert my usual PHP style. Not that that's a bad thing, but it explains my inertia.. I'm up for figuring out ways to make life easier though, so I'm looking into templates now.

Teran answered 19/9, 2008 at 18:54 Comment(1)

This isn't strictly an answer to your question, but given the poor support for function calls in heredoc statements, I usually just generate the strings I'll need before printing the heredoc. Then, I can simply use something like Text {$string1} Text {$string2} Text in the heredoc. – Rockyrococo 6/3, 2018 at 0:21

A

57

I would not use HEREDOC at all for this, personally. It just doesn't make for a good "template building" system. All your HTML is locked down in a string which has several disadvantages

No option for WYSIWYG
No code completion for HTML from IDEs
Output (HTML) locked to logic files
You end up having to use hacks like what you're trying to do now to achieve more complex templating, such as looping

Get a basic template engine, or just use PHP with includes - it's why the language has the <?php and ?> delimiters.

template_file.php

<html>
<head>
  <title><?php echo $page_title; ?></title>
</head>
<body>
  <?php echo getPageContent(); ?>
</body>

index.php

<?php

$page_title = "This is a simple demo";

function getPageContent() {
    return '<p>Hello World!</p>';
}

include('template_file.php');

Athal answered 19/9, 2008 at 19:10 Comment(13)

Unfortunately PHP's method of embedding content makes the resultant HTML very hard to read. It's a shame PHP didn't standardize on short delimiters and provide a shorthand for echo like ASP of old did (which is one of the very few things ASP did better than PHP IMO.) – Peddling 4/9, 2012 at 20:39

There is a shorthand for echo: <?=$valueToEcho;?> or <%=$valueToEcho;%> dependent upon your INI settings. – Athal 5/9, 2012 at 19:26

Most everything I've read about using those shorthands says using them is a bad practice, and I agree. So unfortunately if you are writing code for distribution you can't depend on those INI settings thus making PHP's "support" for them moot for distributed code. FWIW, I've had to fix bugs in other people's WordPress plugins more than once because they used these shorthands. – Peddling 5/9, 2012 at 21:27

I agree, but this is an odd thing to "complain" about. You're basically saying "It's a shame I have to type 7 extra characters" – Athal 6/9, 2012 at 18:32

No, I'm not saying it's a shame I have to type 7 characters; you incorrectly attribute my issues. It's not the typing I'm concerned with, it's the reading. Those characters create lots of visual noise that makes it much harder to scan the source code and understand what the code is doing. For me at least is is MUCH easier to read a HEREDOC. (And BTW, it's 7 character time how ever many times it's used in a given HTML fragment. But I digress.) – Peddling 9/9, 2012 at 21:32

Short is nicer, cleaner and easier to read. In your views <?=$title?> is much nicer than <?php echo $title; ?>. The downside is, yes, for distribution a lot of ini's have short tags off. But, guess what?? As of PHP 5.4, short tags are enabled in PHP regardless of ini settings! So if you're coding with a 5.4+ requirement (let's say you're using traits, for example), go ahead and use those awesome short tags!! – Manicure 14/3, 2013 at 9:57

What's so hard about embedding PHP inside HTML with proper <?php ?> delimiters? It doesn't affect readability. In fact, I think most developers who bellyache about readability are writing poorly formed HTML- more so than PHP. Just remember: one of the P's in the a PHP stands for 'preprocessor'. Use PHP for its strengths, and above all, keep it simple! – Snips 24/7, 2013 at 1:59

By the way, <?= $blah ?> is enabled in 5.4 by default, even if short tags are turned off. – Gutbucket 16/5, 2014 at 16:15

So it turns out that the short answer is "No". You really cannot make a function call directly from within HEREDOC string. It took me quite a moment to grasp this! – Triviality 21/8, 2014 at 15:37

@IfediOkonkwo Actually, you can and there are several answers here that show how. It's just not considered good practice to do so. – Decathlon 21/12, 2014 at 6:27

I couldn't disagree more about wanting to do "more complex templating such as looping" this way. Injecting control flow into an HTML template is the first step to exponentially compounding your complexity. It makes much sense to organize your output data in appropriate data structures first, then use your collection's functions to map/reduce it. It works amazingly well in ReactJS. You should never need a special templating microlanguage to loop. – Clinical 14/9, 2015 at 18:28

The question is about inserting function calls into heredoc strings. It is not about a judgement as to whether it is appropriate or not. That's a judgement call for the person who asked the question. Templating engines are a stupid idea because PHP is already a templating language. – Crumby 26/2, 2018 at 1:48

This seems like the wrong answer to the question. Yes it might not be best practice, but there are situations where you do want to be able to do this. That however isn't the question. – Primp 19/9, 2020 at 14:29

D

79

If you really want to do this but a bit simpler than using a class you can use:

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

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

Decathlon answered 23/5, 2012 at 4:6 Comment(12)

Great @CJDennis! That is the best and cleanest solution for using functions call inside HEREDOC. There is nice resource in some situations. In my site, I use HEREDOC for generate forms with 22 lines of field sets (a HEREDOC block inside a FOR loop ), with function call in order to generate tabindex position. – Cepheus 18/1, 2013 at 4:12

You can even do this: $my_string = "Half the number of seconds since the Unix Epoch: {$fn(time() / 2 . ' Yes! Really!')}"; – Decathlon 29/11, 2013 at 4:33

a more compact definition: $fn = function fn($data) { return $data; }; – Volution 19/9, 2016 at 13:16

@Volution You're right. And even shorter is: $fn = function ($data) { return $data; }; – Decathlon 20/9, 2016 at 2:31

oh, godegolf? okay, let me in: $fn=function($data){return $data;}; rhis should be the shortest – Nadianadine 25/12, 2016 at 22:42

@Nadianadine No, $f=function($d){return$d;}; is shorter, but this is not Code Golf. – Decathlon 27/12, 2016 at 7:8

I didnt even know you could return without space – Nadianadine 27/12, 2016 at 16:57

@Nadianadine Golf? $fn='strval'; – Atabrine 16/12, 2018 at 12:46

@Olivier "{${'fn'}(time())}" and "{$fn(time())}" work exactly the same way. Both need a variable defined. – Decathlon 5/1, 2019 at 12:48

@CJDennis After understanding your answer, I'm sharing my thoughts- It means If we want to call functions inside heredoc then we have to first initialize variables having their values same as the name of the function. Eg :- function phpf1(){}, function phpf2(), function phpf3(){} so if we want to call those functions inside heredoc then we have to make variables like $f1= 'phpf1'; $f2= 'phpf2'; $f3= 'phpf3';. Am I right ? – Seline 11/2, 2020 at 4:27

@AbhishekKamal You could do it that way but having a wrapper function as I set up in my answer makes that unnecessary. "{$fn(phpf1())}, {$fn(phpf2())}, {$fn(phpf3())}" is all you need. Anything that can be a valid function parameter can go inside the parentheses of {$fn()}. – Decathlon 11/2, 2020 at 4:46

Since PHP 7.4, fn is a reserved word. php.net/manual/en/migration74.incompatible.php – Decathlon 5/5, 2020 at 3:16

A

57

I would not use HEREDOC at all for this, personally. It just doesn't make for a good "template building" system. All your HTML is locked down in a string which has several disadvantages

No option for WYSIWYG
No code completion for HTML from IDEs
Output (HTML) locked to logic files
You end up having to use hacks like what you're trying to do now to achieve more complex templating, such as looping

Get a basic template engine, or just use PHP with includes - it's why the language has the <?php and ?> delimiters.

template_file.php

<html>
<head>
  <title><?php echo $page_title; ?></title>
</head>
<body>
  <?php echo getPageContent(); ?>
</body>

index.php

<?php

$page_title = "This is a simple demo";

function getPageContent() {
    return '<p>Hello World!</p>';
}

include('template_file.php');