[RESOLVED] Type Juggling in PHP

r_honey

There are two things I am trying to accompolish with PHP types & arrays. Hope somebody here can help me:

1) You can use

$a = integer;

in PHP. That helps you to recapture the purpose of the variable when you or others visit the code later.
I amtrying to initialize the above variable, i.e. something like

$a = integer =5 ;

$a = integer(5);

All these give parse errors. Is it possible to accompolish what I am trying???

2) You can return an array for indexing with both associative & otherwise, with mysql functions. I need to provide a similar functionality in my library, where users can enter elements in an array using keys, but retrieve it later using numeric indexes in the order in which they were entered.
So, is this feasible???

laserlight

Are you sure of the first example? I have never seen that before, since the integer keyword is used in typecasting to integer.

That helps you to recapture the purpose of the variable when you or others visit the code later.

To capture the purpose of a variable, give it a more descriptive name than $a, and use a comment for further explanation if necessary.

Consider:

$a = 5;

It is clear that $a holds an integer (at least at this point). The purpose of this integer, on the other hand, is unknown. Let us switch to C (or C++ etc) for a moment:

int a = 5;

It is clear that a is an int (integer), and this is something like what you are trying to do. Nonetheless, the purpose of a remains unknown. Let us switch back to PHP:

$score = 5;

Now, we can infer from the name that $score holds some sort of score. Since it has been initialised to an integer, we know it is not a music score, and by looking at the surrounding code, we can more easily determine that it is say, the score of a player for a game, better than if we only had $a to work with.

I need to provide a similar functionality in my library, where users can enter elements in an array using keys, but retrieve it later using numeric indexes in the order in which they were entered.

If you do not actually need the original keys, then just store it as a numerically indexed array, discarding the keys. Alternatively, you can say, duplicate the array, for the two sets of keys, or perhaps make it two dimensional with the inner array consisting of a pair (the associative key, and the value).

r_honey

When I said recapture the purpose, what I meant was the form in which it will be used in the code. Giving it like $index=integer; tells the reader, that $a is meant to be used as an interger index; & $index=string; as a string index.

Alternatively, you can say, duplicate the array, for the two sets of keys, or perhaps make it two dimensional with the inner array consisting of a pair (the associative key, and the value).

That means I would have to provide a wrapper function, that accepts either numeric or string index, & returns the value. I have already done that.
I was looking at a syntax similar to $array[$index]; where both numeric & string indexes could be passed in...

r_honey

Moreover, in function signatures, such as following:

function getElement($index = integer)
{
}

the user of this function knows that he needs to pass in an integer. This was my original purpose. And I was trying to give a default value to the above parameter.

btw, is this syntax in function parameters valid???? The parser does not indicate any error to me.
So, how can I give a default value to it???

bradgrafelman

r_honey wrote:
the user of this function knows that he needs to pass in an integer.

Well, if I ever wanted to educate those viewing my source, I'd probably do:

function getElement($index=0) {
    // OI! You, with the glasses; make sure $index is an INTEGER, got it?
}

r_honey wrote:
btw, is this syntax in function parameters valid???? The parser does not indicate any error to me.
So, how can I give a default value to it???

It should give you a notice about the "use of an undefined constant integer - assumed 'integer'". As for giving it a default value... well, that's the right syntax. In my example code above, I used 0 as the default value (since you said it should be an integer, why should the default be any exception? 😉).

laserlight

the user of this function knows that he needs to pass in an integer. This was my original purpose.

Document the function, either within it as in bradgrafelman's example, or outside (e.g., just before it), as in some phpDocumentor/Doxygen/Javadoc styles. If you really want to be safe, then typecast to int, or even check the type with [man]gettype/man or one of the is_* functions and throw an exception or trigger an error or something.

That means I would have to provide a wrapper function, that accepts either numeric or string index, & returns the value. I have already done that.
I was looking at a syntax similar to $array[$index]; where both numeric & string indexes could be passed in...

Ah, I was rather ambiguous. If you have ever done a print_r() on the array returned by mysql_fetch_array(), you would see that the array is actually duplicated within itself. In other words, using mysql_fetch_row() and mysql_fetch_assoc() will actually return an array half the size (or mysql_fetch_array() returns an array twice the size, depending on your point of view). The array is duplicated because one portion is indexed by numeric keys and the other by string keys, but the values are actually the same.

r_honey

Thanx...

r_honey

What will fetch_array() do then, if a string key itself is say "1".
In that case, I believe the array size would not be exactly double, as there will be only one entry for this key. Right???

Weedpacket

Try it and see...?