How to pass label in PHP? - php

Question

The background of this story is pretty long, so to keep things short -- I know goto is bad, but I have no other choice, because... PHP lacks comma operator.
I have such pattern -- regular function with entry point given as label, and inside it a small lambda which needs to goto to that entry point. Something like this (incorrect code):
function water()
{
_Entry_point_2_0:
// ... some code
(function() { /*...*/ ;goto _Entry_point_2_0;})();
// ... some code
}
I cannot just jump across the function boundaries, so my next idea is to return the label from the lambda and use it as "value" for goto. Something like this:
function water()
{
_Entry_point_2_0:
// ... some code
goto (function() { /*...*/ ;return '_Entry_point_2_0';})();
// ... some code
}
This does not work. Evaluating entire goto as a string eval ('goto _Entry_point_2_0;') does not work either.
The crazy part is I know the label in advance, so you can ask why I cannot write entire function like that:
function water()
{
_Entry_point_2_0:
// ... some code
(function() { /*...*/ ;})();
goto _Entry_point_2_0;
// ... some code
}
The problem is in logic -- executing lambda and goto make 2 expressions now, not one. And I need to make it in one expression -- execute lambda and goto has to be packed in single expression.
I also cannot call recursively the main function because it is whole point of this work, to avoid recursive call :-).
What are the other ways to achieve this?
UPDATE 1 Maybe I rephrase -- what I would like to achieve with goto is continue my_function. Executed from or at the boundary of the inner function (i.e. lambda).
UPDATE 2 The main goal is to loop over the main function, so it is almost equivalent to:
function water()
{
_Entry_point_2_0: while (true)
{
// ... some code
continue (function() { /*...*/ ; return '_Entry_point_2_0'; })();
// ... some code
}
}
"Almost" because of two reasons. I still have the problem with labels exactly as before, and what's more now I have problem where to add breaks to the loop.

Answer 1

So you can't skip a loop iteration from within an anonymous/lambda function. But you could return a value, compare values in the main function and then skip the iteration from there. Sounds simple, right?
Edit: if you also want to break from the lamba, you can use the same strategy.
function water() {
$lambda = function() { /*...*/; };
while (true) {
// Call the lambda function and store the return value.
$return = $lambda();
// If the return value was 'skip this iteration', well... skip it.
// Note: I'd normally compare to false, null or similar.
if ($return == 'skip this iteration') {
continue;
}
elseif ($return == "we're done!") {
break;
}
// Do stuff here.
}
}
I need to make it in one expression -- execute lambda and goto has to be packed in single expression.
So from your last comment I now partly understand why you have this requirement. But it's still not entirely clear. You have written a script to inject this code into some pre-existing function(s) and don't know the surroundings. But are the goto labels already in place? In any case, perhaps your problem is as simple as this: you want the code to be a single line only. But that's possible, code can span only a single line in PHP. It's not the prettiest, but it works just fine.
function water() {
while (true) {
if (function() { /*...*/; }() == 'skip this iteration') { continue; /* Or goto */ }
// Do stuff here.
}
}

Answer 2

Perhaps you are trying to solving your attemted solution rather than your original problem. This question smells XY problem.
_Entry_point_2_0:
// ... some code
(function() { /*...*/ ;goto _Entry_point_2_0;})();
Looks for me like do while loop:
do {
// ... some code
} while ((function() { /*...*/ ; return $k !== 0;})());
Now applying an anonymous function like that is not allowed. In addition closure parameters need to be explicitly declared. Thus my solution needs to be written like this:
$k = 10;
$f = function() use (&$k) { /*...*/ ; return $k !== 0; };
do {
// some code
} while ( $f() );
If you want to have a "comma operator" you just make a function that takes any numbers of argumens and return the last:
function begin(){
return func_get_args()[func_num_args()-1];
}
begin(expression1, expression2, expression3); // ==> result of expression3
All of a function arguments gets evaluated so it does the same given that the arguments are not dependent on each other.

Answer 3

Im fairly sure this is impossible by design.
Annonymous functions require all "state" to be passed in via a use statement. You can not pass a label as a reference
PHP Parse error: syntax error, unexpected '_Entry_point_2_0'
(T_STRING), expecting '&' or variable (T_VARIABLE)
The function is running in its own scope with no reference to the label which means it would need to be passed back somehow.
goto docs have the following
This is not a full unrestricted goto. The target label must be within the same file and context, meaning that you cannot jump out of a function or method, nor can you jump into one.
its also invalid to pass a variable to goto
PHP Parse error: syntax error, unexpected '$goto' (T_VARIABLE), expecting identifier (T_STRING)
Though all of this is probably a good thing, as goto suggests the logic flow is wrong, You will be able to find a way to structure this that is more corect and does not require a go to.
Edit:
After update 2 why not do
if(your lambda() == something) {
Continue;
}
Sorry wrote the code on my phone. That seems to do the same thing and is much more readable

Answer 4

You can use recursion:
function myFunc($i = 0) {
if ($i < 10) { //or any other logic to prevent "infinite loop"
//Main code
myFunc($i++);
}
}