It was kind of hard for me to form this as a title. Basically what I have is a simple laravel-like router that saves allowed locations in an array. My question is if I could supply some arguements dynamically through that array's elements. I think I did even worse in the body of the question so let me just give a simple example:
class Example(){
public function display($bool){
if($bool){
echo 'hey';
}else{
echo 'bye';
}
}
}
Now if you wanna call this class' method from somewhere else with a variable
$var = 'display';
$example = new Example();
$example->$var(true);
And you get 'hey', but what if I can only control the $var = 'display' part, and the code below is beyond my control. Can I still pass a value to that method? Something like
$var = 'display(true)';
$example = new Example();
$example->$var;
Not without some epic string parsing.
More importantly, if you need this, something that you're doing is horribly wrong.
Related
I've recently worked on some code in which I had to dynamically call a method inside a class.
The solution I ended up using was 2 lines, because the "dynamic" part was only a small section of the actual method name that I needed to call.
This is the solution I ended up using:
$pull = "pull_{$type}_day";
$day = $download->$pull();
Originally, I tried to make this a single line, but it did not work. In a technical sense, why does the above code work but the below code does not?
$day = $download->"pull_{$type}_day"();
If you use a string or part of a string as a method (or property) you need to surround it in {} like this:
#property
echo $foo->{"bar"};
#method call
echo $foo->{"bar"}();
So if you need a variable in the string part, this follows the same rules as any normal string.
echo $foo->{"bar".$bar}();
echo $foo->{'bar'.$bar.'bar'}();
echo $foo->{"bar{$bar}bar"}();
And so on. Here is a full example
class foo{
function pull_1_day(){
echo "bar";
}
}
$a = 1;
(new foo)->{"pull_{$a}_day"}();
Outputs
bar
Sandbox
This follows in the same way PHP allows you to use a string as a variable such as this:
$foo = 'bar';
echo ${"foo"};
Outputs
bar
Sandbox
Same kind of syntax.
Why not use call_user_func()?
I find it easier to read and parse.
Assuming you have:
class pull {
public function pull_foo_day () {
echo "hello";
}
}
$pull = new pull();
$type = "foo";
You can simply do:
call_user_func([$pull, "pull_{$type}_day"]);
Outputs:
hello
See it working here.
If I have code like this
$myFunction = new classFoo(); //ie. class
$myFunction-> new functionBar($value1,$value2,$value3); //ie. function
I understand in a normal scenario, if I had this function...
function functionBar($value1,$value2,$value3){
$answer=$value1+$value2+$value3
return $answer
}
I could then plug into it like this
$answer=functionBar(1,2,3)
I could expect an echo of $answer to be 6, correct?
If I'm wrong there let me know, because my real issue is that the function is wrapped in a variable, which if I examine through console has what I need in it, but I can't get my head around how to access it with that extra layer involved.
because my real issue is that the function is wrapped in a variable
[snip] but I can't get my head around how to access it with that extra
layer involved.
Using your code and var names, and I've added the function which you do understand inside the class (is simply a function (aka "method") which essentially does the same thing - there are differences but not within the scope of your question).
It returns a value, which you can "wrap" (store) in a variable just the same as the function does without the class:
$myFunction = new foo();
$answer = $myFunction->functionBar(10, 20, 30);
class foo
{
public function functionBar($value1, $value2, $value3)
{
return $value1 + $value2 + $value3;
}
}
Your $answer var would contain "60". echoing it out would echo "60".
I have a strange question that's probably not possible, but it's worth asking in case there are any PHP internals nerds who know a way to do it. Is there any way to get the variable name from a function call within PHP? It'd be easier to give an example:
function fn($argument) {
echo SOME_MAGIC_FUNCTION();
}
$var1 = "foo";
$var2 = "bar";
fn($var1); // outputs "$var1", not "foo"
fn($var2); // outputs "$var2", not "bar"
Before you say it - yes, I know this would be a terrible idea with no use in production code. However, I'm migrating some old code to new code, and this would allow me to very easily auto-generate the replacement code. Thanks!
debug_backtrace() returns information about the current call stack, including the file and line number of the call to the current function. You could read the current script and parse the line containing the call to find out the variable names of the arguments.
A test script with debug_backtrace:
<?php
function getFirstArgName() {
$calls=debug_backtrace();
$nearest_call=$calls[1];
$lines=explode("\n", file_get_contents($nearest_call["file"]));
$calling_code=$lines[$nearest_call["line"]-1];
$regex="/".$nearest_call["function"]."\\(([^\\)]+)\\)/";
preg_match_all($regex, $calling_code, $matches);
$args=preg_split("/\\s*,\\s*/", $matches[1][0]);
return $args[0];
}
function fn($argument) {
echo getFirstArgName();
}
$var1 = "foo";
$var2 = "bar";
fn($var1);
fn($var2);
?>
Output:
$var1$var2
Anyone has an idea if this is at all possible with PHP?
function foo($var) {
// the code here should output the value of the variable
// and the name the variable has when calling this function
}
$hello = "World";
foo($hello);
Would give me this output
varName = $hello
varValue = World
EDIT
Since most people here 'accuse' me of bad practices and global variables stuff i'm going to elaborate a little further on why we are looking for this behaviour.
the reason we are looking at this kind of behaviour is that we want to make assigning variables to our Views easier.
Most of the time we are doing this to assign variables to our view
$this->view->assign('products', $products);
$this->view->assign('members', $members);
While it would be easier and more readable to just be able to do the following and let the view be responsible to determining the variable name the assigned data gets in our views.
$this->view->assign($products);
$this->view->assign($members);
Short answer: impossible.
Long answer: you could dig through apd, bytekit, runkit, the Reflection API and debug_backtrace to see if any obscure combination would allow you to achieve this behavior.
However, the easiest way is to simply pass the variable name along with the actual variable, like you already do. It's short, it's easy to grasp, it's flexible when you need the variable to have a different name and it is way faster than any possible code that might be able to achieve the other desired behavior.
Keep it simple
removed irrelevant parts after OP edited the question
Regardless of my doubt that this is even possible, I think that forcing a programmer on how to name his variables is generally a bad idea. You will have to answer questions like
Why can't I name my variable $arrProducts instead of $products ?
You would also get into serious trouble if you want to put the return value of a function into the view. Imagine the following code in which (for whatever reason) the category needs to be lowercase:
$this->view->assign(strtolower($category));
This would not work with what you're planning.
My answer therefore: Stick to the 'verbose' way you're working, it is a lot easier to read and maintain.
If you can't live with that, you could still add a magic function to the view:
public function __set($name, $value) {
$this->assign($name, $value);
}
Then you can write
$this->view->product = $product;
I don't think there is any language where this is possible. That's simply not how variables work. There is a difference between a variable and the value it holds. Inside the function foo, you have the value, but the variable that held the value is not available. Instead, you have a new variable $var to hold that value.
Look at it like this: a variable is like a bucket with a name on it. The content (value) of the variable is what's inside the bucket. When you call a function, it comes with its own buckets (parameter names), and you pour the content of your bucket into those (well, the metaphor breaks down here because the value is copied and still available outside). Inside the function, there is no way to know about the bucket that used to hold the content.
What you're asking isn't possible. Even if it was, it would likely be considered bad practice as its the sort of thing that could easily get exploited.
If you're determined to achieve something like this, the closest you can get would be to pass the variable name as a string and reference it in the function from the $GLOBALS array.
eg
function this_aint_a_good_idea_really($var) {
print "Variable name: {$var}\n";
print "Variable contents: {$GLOBALS[$var]}\n";
}
$hello="World";
this_aint_a_good_idea_really('hello');
But as I say, that isn't really a good idea, nor is it very useful. (Frankly, almost any time you resort to using global variables, you're probably doing something wrong)
Its not impossible, you can find where a function was invoked from debug_backtrace() then tokenize a copy of the running script to extract the parameter expressions (what if the calling line is foo("hello $user, " . $indirect($user,5))?),
however whatever reason you have for trying to achieve this - its the wrong reason.
C.
Okay, time for some ugly hacks, but this is what I've got so far, I'll try to work on it a little later
<?php
class foo
{
//Public so we can test it later
public $bar;
function foo()
{
//Init the array
$this->bar = array();
}
function assign($__baz)
{
//Try to figure out the context
$context = debug_backtrace();
//assign the local array with the name and the value
//Alternately you can initialize the variable localy
//using $$__baz = $context[1]['object']->$__baz;
$this->bar[$__baz] = $context[1]['object']->$__baz;
}
}
//We need to have a calling context of a class in order for this to work
class a
{
function a()
{
}
function foobar()
{
$s = "testing";
$w = new foo();
//Reassign local variables to the class
foreach(get_defined_vars() as $name => $val)
{
$this->$name = $val;
}
//Assign the variable
$w->assign('s');
//test it
echo $w->bar['s'];
}
}
//Testrun
$a = new a();
$a->foobar();
impossible - the max. ammount of information you can get is what you see when dumping
debug_backtrace();
Maybe what you want to do is the other way around, a hackish solution like this works fine:
<?php
function assign($val)
{
global $$val;
echo $$val;
}
$hello = "Some value";
assign('hello');
Ouputs: Some value
What you wish to do, PHP does not intend for. There is no conventional way to accomplish this. In fact, only quite extravagant solutions are available. One that remains as close to PHP as I can think of is creating a new class.
You could call it NamedVariable, or something, and as its constructor it takes the variable name and the value. You'd initiate it as $products = new NamedVariable('products', $productData); then use it as $this->view->assign($products);. Of course, your declaration line is now quite long, you're involving yet another - and quite obscure - class into your code base, and now the assign method has to know about NamedVariable to extract both the variable name and value.
As most other members have answered, you are better off suffering through this slight lack of syntactic sugar. Mind you, another approach would be to create a script that recognizes instances of assign()'s and rewrites the source code. This would now involve some extra step before you ran your code, though, and for PHP that's silly. You might even configure your IDE to automatically populate the assign()'s. Whatever you choose, PHP natively intends no solution.
This solution uses the GLOBALS variable. To solve scope issues, the variable is passed by reference, and the value modified to be unique.
function get_var_name(&$var, $scope=FALSE) {
if($scope) $vals = $scope;
else $vals = $GLOBALS;
$old = $var;
$var = $new = 'unique'.rand().'value';
$vname = FALSE;
foreach ($vals as $key => $val) {
if($val === $new) $vname = $key;
}
$var = $old;
return $vname;
}
$testvar = "name";
echo get_var_name($testvar); // "testvar"
function testfunction() {
$var_in_function = "variable value";
return get_var_name($var_in_function, get_defined_vars());
}
echo testfunction(); // "var_in_function"
class testclass {
public $testproperty;
public function __constructor() {
$this->testproperty = "property value";
}
}
$testobj = new testclass();
echo get_var_name($testobj->testproperty, $testobj); // "testproperty"
Is there any way to emulate a structure class in PHP? ie a class which passes by value and not by reference, so it can still be type hinted...
And if so, what different techniques could be used? What's the best technique?
If this is possible you could obviously create a fully type safe layer for PHP, are there such layers? Has anyone had any experience with this?
Objects are always passed by reference. The only way to make them pass as a copy is to explicitly use the clone keyword (yes, everywhere).
My recommendation would be to use an array, which are value types and thus always copied. Since you can use it as an associative array (eg string -> value), it might as well be an object. The downside is, of course, you can't use methods (but that's like a struct so you may be happy with this). There is no way to enforce type safety, however.
But with all your requirements it sounds like PHP isn't your kind of language, to be honest.
I think the easiest way is to do it like java does - have your value classes be immutable, and let all "modification" methods return a new object instead.
I don't think you can achieve that goal, only with PHP code.
You have no control on how PHP function handle parameters, and I don't see how you could make sure everything is handled the way you want, without having to change the (lower-level) code in the PHP binary and modules.
It would be pretty cool, though :)
I was playing around with anonymous's suggestion to make any mutations of the object return a new object, and this works, but it's awkward.
<?php
class FruityEnum {
private $valid = array("apple", "banana", "cantaloupe");
private $value;
function __construct($val) {
if (in_array($val, $this->valid)) {
$this->value = $val;
} else {
throw new Exception("Invalid value");
}
}
function __set($var, $val) {
throw new Exception("Use set()!!");
}
function set(FruityEnum &$obj, $val) {
$obj = new FruityEnum($val);
}
function __get($var) { //everything returns the value...
return $this->value;
}
function __toString() {
return $this->value;
}
}
And now to test it:
function mutate(FruityEnum $obj) { // type hinting!
$obj->set($obj, 'banana');
return $obj;
}
$x = new FruityEnum('apple');
echo $x; // "apple"
$y = mutate($x);
echo $x // still "apple"
. $y // "banana"
It works, but you have to use a strange way to change the object:
$obj->set($obj, 'foo');
The only other way I could think to do it would be to use the __set() method, but that was even worse. You had to do this, which is bloody confusing.
$obj = $obj->blah = 'foo';
In the end, it's probably easier to make the variables private and provide no mutators, so the only way to change a variable's "enum" value would be to create a new one:
echo $obj; // "banana"
$obj = new FruityEnum("cantaloupe");