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I'm attempting to create a function with flags as its arguments but the output is always different with what's expected :

define("FLAG_A", 1);  
define("FLAG_B", 4);  
define("FLAG_C", 7);  
function test_flags($flags) {  
 if($flags & FLAG_A) echo "A";  
 if($flags & FLAG_B) echo "B";  
 if($flags & FLAG_C) echo "C";   
}  
test_flags(FLAG_B | FLAG_C); # Output is always ABC, not BC  

How can I fix this problem?

 Answers

3

Flags must be powers of 2 in order to bitwise-or together properly.

define("FLAG_A", 0x1);
define("FLAG_B", 0x2);
define("FLAG_C", 0x4);
function test_flags($flags) {
  if ($flags & FLAG_A) echo "A";
  if ($flags & FLAG_B) echo "B";
  if ($flags & FLAG_C) echo "C";
}
test_flags(FLAG_B | FLAG_C); # Now the output will be BC

Using hexadecimal notation for the constant values makes no difference to the behavior of the program, but is one idiomatic way of emphasizing to programmers that the values compose a bit field. Another would be to use shifts: 1<<0, 1<<1, 1<<2, &c.

Tuesday, November 8, 2022
5

They are just constants which map to a number, e.g. SORT_NUMERIC (a constant used by sorting functions) is the integer 1.

Check out the examples for json_encode().

As you can see, each flag is 2n. This way, | can be used to specify multiple flags.

For example, suppose you want to use the flag JSON_FORCE_OBJECT (16 or 00010000) and JSON_PRETTY_PRINT (128 or 10000000).

The bitwise operator OR (|) will turn the bit on if either operand's bit is on...

JSON_FORCE_OBJECT | JSON_PRETTY_PRINT

...is internally....

00010000 | 1000000

...which is...

10010000

You can check it with...

var_dump(base_convert(JSON_PRETTY_PRINT | JSON_FORCE_OBJECT, 10, 2));
// string(8) "10010000"

CodePad.

This is how both flags can be set with bitwise operators.

Monday, October 24, 2022
2

The array_reduce will reduce an array to a single value for you:

$res = array_reduce($array, function($a, $b) { return $a | $b; }, 0);

Reduce is also sometimes called fold (fold left or fold right) in other languages.

Monday, August 15, 2022
 
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 ");
value: hello 
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 > $myVal = myOuterFunc("Hello ");
php > var_dump($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 > $myVal = myOuterFunc("Hello ");
Hello 
php > var_dump($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 ");
value: Hello 
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 ");
value: Hello 
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 ");
value: Hello 
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 ");
value: Hello 
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.

Tuesday, December 20, 2022
 
5

You can't exceed 64 bits on a 64 bit value, not even using the "negative space". If you have 64 bits, you have 64 bits. You can use a Guid to get 128 bits, which will put the problem off for a while, but ultimately you will need to add additional fields.

Saturday, November 26, 2022
 
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