Asked  1 Year ago    Answers:  5   Viewed   11 times

Possible Duplicate:
Are global variables in PHP considered bad practice? If so, why?
global in functions

Edit: question answered in link above.

No, "global" in php is not the same thing as global in other languages, and while it does not introduce any security problems it can make the code less comprehensible to others.


OP:

Project summary - I am writing a web CMS to get my feet wet with PHP / MySQL. In order to break up the code I have a concept of these basic tiers / modules:

Data
- MySQL Tables
- PHP Variables

Function
- SQL - Get / Set / etc
- Frontend - Showing pages
- Backend - Manager

Presentation
- HTML Templates
- Page Content
- CSS Stylesheets

The goal is common enough. Use MySQL to hold site settings and page content, use php to get / manipulate content data for a page being served, then insert into an html template and echo to browser. Coming from OO languages like C# the first problem I ran into was variable scope issues when using includes and functions.

From the beginning I had been writing function-only php files and including them where needed in other files that had existing variable array definitions. For example, ignoring the data tier for a moment, a simple page might generically look like this:

File 1 (page)

$DATA_PAGE = Array
(
  'temp'  = null,
  'title' = null,
  [...]
);

include 'functions.php';

get_data ( 'page.php' );

[...]

run_html ();

File 2 (functions)

function get_data ( $page_name )
{
  global $DATA_PAGE;

  $DATA_PAGE [ 'temp'  ] = 'template';
  $DATA_PAGE [ 'title' ] = 'test page';
  [...]
}

function run_html ()
{
  global $DATA_PAGE;

  echo '<html>';
  echo '<head>';
  echo '<title>' . $DATA_PAGE [ 'title' ] . '</title>';
  [...]
}

I chose this method for a few reasons:

  • The data in these arrays after sql fetch might be used anywhere, including page content
  • I didnt want to have a dozen function arguments, or pass entire arrays

The code runs great. But in every article I find on the subject, the "global" calls in my functions are called bad practice, even though the articles never state why? I thought all that meant was "use parent scope". Am in introducing a security hole into my app? Is there a better method? Thanks in advance.

 Answers

2

I think a top reason for avoiding this is that it hides dependencies.

Your functions get_data and run_html do not advertise in any way that they share data, and yet they do, in a big way. And there is no way (short of reading the code) to know that run_html will be useless if get_data has not been called.

As the complexity of your codebase grows, this kind of lurking dependency will make your code fragile and hard to reason about.

Friday, June 11, 2021
 
2

Cracks knuckles

Technically the syntax is "correct" (it won't generate a fatal error) but the semantics of PHP render it effectively meaningless in its current form. Let's look at a few things first, namely how PHP handles the assignment of named functions to variables:

php > echo shell_exec("php -v");
PHP 5.4.16 (cli) (built: Oct 30 2018 19:30:51)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2013 Zend Technologies

php > function speak($arg) {echo "{$arg}n";}
php > function give($arg) {return $arg;}
php > $speak = speak(4);
4
php > $give = give(4);
php > var_dump($speak);
NULL
php > var_dump($give);
int(4)

The function itself is executed upon assignment and its return value (NULL or otherwise) is assigned to the variable. Since we're only assigning the return value of a function's execution, trying to use this variable as a function name has no use:

php > $speak(4);
php > $give(4);
php >

Let's contrast this to the assignment of an anonymous function (a.k.a. a 'Closure'):

php > $min = 1; $max = 6;
php > $checkName = function ($value) use ($min, $max) {
php {   echo "value: {$value}n";
php {   echo "min: {$min}n";
php {   echo "max: {$max}n";
php { };
php > var_dump($checkName);
object(Closure)#1 (2) {
  ["static"]=>
  array(2) {
    ["min"]=>
    int(1)
    ["max"]=>
    int(6)
  }
  ["parameter"]=>
  array(1) {
    ["$value"]=>
    string(10) "<required>"
  }
}

Unlike some other languages, a closure is represented in PHP by an actual Object. Variables inside the 'use' clause are imported at the time the Closure was created; function parameters (i.e. $value) have their values captured when the Closure is called (hence why we see it noted as a required parameter and not a static value). The semantics of references within Closures aren't worth considering right now but if you want further reading, goat's answer to this question is a great start.

The major takeaway here is that the Closure's assignment to $checkName did not execute the Closure itself. Instead, $checkName becomes a sort of "alias" we can use to reference this function by name:

php > $checkName("hello stackoverflow");
value: hello stackoverflow
min: 1
max: 6
php >

Given how loose PHP is about the number of function parameters passed, a zero-parameter execution returns expected results:

php > $checkName();
value:
min: 1
max: 6
php >

Now let's take it another level deeper and define a function within a function:

php > function myOuterFunc($arg) {
php {   function myInnerFunc($arg){
php {     echo "{$arg}n";
php {   }
php { }
php > $myVal = myOuterFunc("Hello stackoverflow");
php > var_dump($myVal);
NULL
php >

By now this result should make sense. Functions do not execute unless explicitly called; just because we call myOuterFunc doesn't mean we execute any function code defined inside of it. That's not to say that we couldn't:

php > function myOuterFunc($arg) {
php {   function myInnerFunc($arg){
php {     echo "{$arg}n";
php {   }
php {   myInnerFunc($arg);
php { }
php > $myVal = myOuterFunc("Hello stackoverflow");
Hello stackoverflow
php > var_dump($myVal);
NULL
php >

Which brings us back around to what is essentially your question: what about a named function inside of a Closure? Given what we've now discovered about function execution, we can generate a series of very predictable examples:

$min = 1; $max = 6;
$checkName = function ($value) use ($min, $max) {
  function question(){echo "How are youn";}
  echo "value: {$value}n";
  echo "min: {$min}n";
  echo "max: {$max}n";
};
php > $checkName("Hello stackoverflow");
value: Hello stackoverflow
min: 1
max: 6
php >

As expected, the named function's code inside the Closure is not executed because we have not explicitly called it.

php > $min = 1; $max = 6;
php > $checkName = function ($value) use ($min, $max) {
php {   function question(){echo "How are youn";}
php {   echo "value: {$value}n";
php {   echo "min: {$min}n";
php {   echo "max: {$max}n";
php {   question();
php { };
php > $checkName("Hello stackoverflow");
value: Hello stackoverflow
min: 1
max: 6
How are you
php >

Explicitly calling the inner function works just fine, provided we define that function before we call it:

php > $min = 1; $max = 6;
php > $checkName = function ($value) use ($min, $max) {
php {   echo "value: {$value}n";
php {   echo "min: {$min}n";
php {   echo "max: {$max}n";
php {   question();
php {   function question(){echo "How are youn";}
php { };
php > $checkName("Hello stackoverflow");
value: Hello stackoverflow
min: 1
max: 6
php >

php > $min = 1; $max = 6;
php > $checkName = function ($value) use ($min, $max) {
php {   echo "value: {$value}n";
php {   echo "min: {$min}n";
php {   echo "max: {$max}n";
php {   function question(){echo "How are youn";}
php {   question();
php { };
php > $checkName("Hello stackoverflow");
value: Hello stackoverflow
min: 1
max: 6
How are you
php >

So to the point of your questions then:

  1. Yes it's legal and what you're attempting is possible but semantically meaningless in its current form.

  2. Any named functions inside the Closure definitely do not reside in the global namespace, they are within the scope of their defining Closure. FWIW, the term "members" typically refers to class variables (usually called "properties" in PHP). While Closures are an Object and let you duplicate the functionality of instance variables found within classes, they should not be confused or construed with classes in any way.

3/4) Not how you're trying to use it, no. Nothing outside of the Closure has any concept of the functions inside; if in calling your Closure code, said code performs operations using the inner functions, then they will see the light of day. But there is no immediate way to reference those inner functions as if they were defined outside of the Closure's scope.

In other words, the only way you'll get those inner functions to execute is if a) that code is specifically executed by the Closure's code and b) you execute said Closure code.

Hope this helps.

Saturday, May 29, 2021
 
TMichel
 
5

Because cursors take up memory and create locks.

What you are really doing is attempting to force set-based technology into non-set based functionality. And, in all fairness, I should point out that cursors do have a use, but they are frowned upon because many folks who are not used to using set-based solutions use cursors instead of figuring out the set-based solution.

But, when you open a cursor, you are basically loading those rows into memory and locking them, creating potential blocks. Then, as you cycle through the cursor, you are making changes to other tables and still keeping all of the memory and locks of the cursor open.

All of which has the potential to cause performance issues for other users.

So, as a general rule, cursors are frowned upon. Especially if that's the first solution arrived at in solving a problem.

Wednesday, June 2, 2021
2

For a chess like game such as you are developing, there is nothing inherently wrong with using absolute positioning. As you said, relative positioning and normal flow layout make this sort of task quite difficult.

Of course, if you were developing a more standard website, such as a site providing some public service, absolute positioning overrides the default flow layout of browsers and so will reduce accessibility for many users. In this case I would avoid it.

Having said that, a lesser known benefit of absolute positioning is that it allows localized absolute positioning within the nearest "positioned" parent element.

Note: A "positioned" element can be any of the following: relative, fixed, absolute, or sticky.

To explain:

<div id="parentDIV" style="position:relative">
    <div id="childDIV" style="position:absolute;left:20px;top:20px;">
          I'm absolutely positioned within parentDIV.
    </div>
</div>

Here, childDIV is actually positioned 20px from the left and 20px from the top of parentDIV, NOT the overall document. This gives a nice precise control over nested elements on a page, without sacrificing the overall page flow-layout.

So to answer your question (relative positioning being preferred over absolute): I don't believe there is a correct answer, it depends on what you are needing to build. However in general positioning (absolute or relative) versus default flow layout, my approach is as described above.

Wednesday, June 9, 2021
5

In PHP all functions are always global, no matter how or when you define them. (Anonymous functions are partially an exception to this.) Both your function definitions will thus be global.

From the documentation:

All functions and classes in PHP have the global scope - they can be called outside a function even if they were defined inside and vice versa.

Wednesday, August 11, 2021
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