Asked  7 Months ago    Answers:  5   Viewed   152 times
function foo () {
    global $var;
    // rest of code

In my small PHP projects I usually go the procedural way. I generally have a variable that contains the system configuration, and when I nead to access this variable in a function, I do global $var;.

Is this bad practice?



When people talk about global variables in other languages it means something different to what it does in PHP. That's because variables aren't really global in PHP. The scope of a typical PHP program is one HTTP request. Session variables actually have a wider scope than PHP "global" variables because they typically encompass many HTTP requests.

Often (always?) you can call member functions in methods like preg_replace_callback() like this:

preg_replace_callback('!pattern!', array($obj, 'method'), $str);

See callbacks for more.

The point is that objects have been bolted onto PHP and in some ways lead to some awkwardness.

Don't concern yourself overly with applying standards or constructs from different languages to PHP. Another common pitfall is trying to turn PHP into a pure OOP language by sticking object models on top of everything.

Like anything else, use "global" variables, procedural code, a particular framework and OOP because it makes sense, solves a problem, reduces the amount of code you need to write or makes it more maintainable and easier to understand, not because you think you should.

Wednesday, March 31, 2021
answered 7 Months ago

They clutter up the global namespace and are slower to look up than local variables.

First of all, having many global variables is always a bad thing because it's easy to forget you declared a variable somewhere and accidentally re-declare it somewhere else. If your first variable was local then you don't have a problem. If it was global, then it just got overwritten. This gets even worse when you get into implied globals (e.g. when you say someVar = someValue without declaring someVar with the var keyword).

Secondly, global variables take longer for Javascript to "find" than local variables. The difference in speed isn't huge, but it does exist.

For further reading and a more in-depth explanation of why globals are considered bad practice, you may want to check out this page.

Tuesday, June 1, 2021
answered 5 Months ago

The reason is that the line

stringvar = "bar"

is ambiguous, it could be referring to a global variable, or it could be creating a new local variable called stringvar. In this case, Python defaults to assuming it is a local variable unless the global keyword has already been used.

However, the line

dictvar['key1'] += 1

Is entirely unambiguous. It can be referring only to the global variable dictvar, since dictvar must already exist for the statement not to throw an error.

This is not specific to dictionaries- the same is true for lists:

listvar = ["hello", "world"]

def listfoo():
    listvar[0] = "goodbye"

or other kinds of objects:

class MyClass:
    foo = 1
myclassvar = MyClass()

def myclassfoo(): = 2

It's true whenever a mutating operation is used rather than a rebinding one.

Wednesday, June 9, 2021
answered 5 Months ago

Here is what the book says on page 205:

If you’re familiar with operating system architecture, you might be interested to know that local variables and function arguments are stored on the stack, while global and static variables are stored on the heap.

This is definitely an error in the book. First, one should discuss storage in terms of storage duration, the way C++ standard does: "stack" refers to automatic storage duration, while "heap" refers to dynamic storage duration. Both "stack" and "heap" are allocation strategies, commonly used to implement objects with their respective storage durations.

Global variables have static storage duration. They are stored in an area that is separate from both "heap" and "stack". Global constant objects are usually stored in "code" segment, while non-constant global objects are stored in the "data" segment.

Tuesday, June 22, 2021
answered 4 Months ago

What you should really do is pass the variable to the function instead of using a global at all.

An example how to change a variable outside of the function via passing it as reference parameter:

function myFunc(&$myVar)
    $myVar = 10;

$foo = 0;
var_dump($foo); // yields 10
Tuesday, June 29, 2021
answered 4 Months ago
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