zestyping: Why PHP should never be taught.

Ping (

zestyping) wrote,
@ 2005-06-09 10:11:00

Why PHP should never be taught.

Suppose A equals B, and also B equals C. Any reasonable person would expect that A equals C, right?

Oh yeah?

% cat equality.php
<?php

$a = 0;
$b = "eggs";
$c = "spam";

print ($a == $b) ? "a == b\n" : "a != b\n";
print ($b == $c) ? "b == c\n" : "b != c\n";
print ($a == $c) ? "a == c\n" : "a != c\n";
print ($a == $d) ? "a == d\n" : "a != d\n";
print ($b == $d) ? "b == d\n" : "b != d\n";
print ($c == $d) ? "c == d\n" : "c != d\n";

?>

% php equality.php
a == b
b != c
a == c
a == d
b != d
c != d

%

Try explaining that to a first-time programmer.

Update (2007-12-11): It gets even worse. Check this out.

Page 1 of 2
<<	[1] [2]	>>

(101 comments) - (Post a new comment)

	nibot 2005-06-09 05:32 pm UTC (link)
	Why PHP shouldn't be taught? This is why PHP shouldn't exist. (Reply to this) (Thread)

	but, as a practical matter josephgrossberg 2007-12-12 07:57 pm UTC (link)
	PHP is free, an easy next-step for people familiar with HTML, and has a huge user base. Yes, it has its flaws, but if someone is relatively new to web development, and is building on a Linux/Apache server, what would you suggest? (Reply to this) (Parent)(Thread)(Expand)

Re: but, as a practical matter -

boffo9, 2007-12-12 08:48 pm UTC (Expand)

Added to My Memories

r6
2005-06-09 06:46 pm UTC (link)

This is even worse than being referentially opaque.

(Reply to this) (Thread)

(Reply from suspended user)

	rebbyribs 2005-06-09 07:02 pm UTC (link)
	So 0 has a special meaning that wouldn't be intuitively obvious? I guess I don't understand how that's so much worse than the rest of the symbols being not intuitively obvious ($ ; != = vs ==). It's pretty much all confusing when you're a first-time programmer, and it just seems like a bunch of picky arbitrary rules to remember. (Reply to this) (Thread)

	(Anonymous) 2007-12-11 11:02 pm UTC (link)
	There's a difference between 'intuitively obvious' and 'mathematically correct.' (Reply to this) (Parent)(Thread)(Expand)

(no subject) - (Anonymous), 2007-12-11 11:09 pm UTC (Expand)

(no subject) -

vityok, 2007-12-12 06:55 am UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 09:55 am UTC (Expand)

duaiwe
2005-06-09 07:07 pm UTC (link)

I fail to see how PHP's overloading equality operators makes it necessarily a bad language. The meaning of the equality operators is entirely dependent on context. Not unlike overloading operators in C++.

A poor language to start first time programmers on? Very likely, I'd start with something like C that's a lot more strict. But that one example doesn't condemn the entire language.

(Reply to this) (Thread)(Expand)

	eevee 2007-12-11 09:54 pm UTC (link)
	Right; it's the eight billion other rough edges and hacks and tacked-on half-assed features that condemn the language. (Reply to this) (Parent)(Thread)(Expand)

(no subject) -

jib.myopenid.com, 2007-12-12 03:48 am UTC (Expand)

(no subject) -

eevee, 2007-12-12 04:16 pm UTC (Expand)

(Reply from suspended user)

	trinity_gal 2005-06-09 07:12 pm UTC (link)
	b and c don't even look like integers... seems like any string equals zero how does php define equality?? is there any usefulness for php defining equality like this? (Reply to this) (Thread)(Expand)

	zestyping 2005-06-09 08:28 pm UTC (link)
	Hi! :) In PHP, whenever you compare a string to a number, PHP always tries to convert the string to a number. (Crazy, in my opinion.) If the string doesn't look anything like a number, the conversion yields zero without any warning. (Reply to this) (Parent)(Thread)(Expand)

(no subject) - (Anonymous), 2007-12-11 10:46 pm UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 02:24 am UTC (Expand)

(no subject) -

eevee, 2007-12-12 04:58 pm UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 02:46 am UTC (Expand)

Non-sequitor - (Anonymous), 2009-07-30 03:59 pm UTC (Expand)

(Reply from suspended user)

	_rowan_tree_ 2005-06-09 09:04 pm UTC (link)
	That's why languages should have explicit types! (Reply to this) (Thread)(Expand)

	misuba 2005-06-09 09:45 pm UTC (link)
	*TWEEEEEEET* Technical foul: over-obvious trolling. Five yard penalty. (Reply to this) (Parent)(Thread)(Expand)

(no subject) -

eigenvalue, 2005-06-10 03:12 pm UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 03:07 am UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 05:38 am UTC (Expand)

(no subject) -

praetorian42, 2007-12-12 01:21 pm UTC (Expand)

(no subject) -

_rowan_tree_, 2007-12-12 03:16 pm UTC (Expand)

	jerub 2005-06-10 05:01 am UTC (link)
	Also, the boolean type 'True' is a bastard of a thing in php. Watch this: <?php function myFunc($foo) { if ($foo == 'abc') { echo "AbcCase\n"; } if ($foo == 'bar') { echo "FooCase\n"; } } myFunc(True); ?> AbcCase FooCase (Reply to this) (Thread)(Expand)

	(Anonymous) 2005-06-10 07:39 am UTC (link)
	maybe you can try with the "===" operator (Reply to this) (Parent)(Thread)(Expand)

(no subject) -

jerub, 2005-06-10 08:59 am UTC (Expand)

(no subject) -

misuba, 2005-06-10 06:52 pm UTC (Expand)

(no subject) - (Anonymous), 2007-12-11 11:11 pm UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 01:09 am UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 05:41 am UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 03:56 pm UTC (Expand)

Python

r6
2005-06-13 02:05 pm UTC (link)

$ python -V
Python 2.4.1
$ python
>>> a = 10000000000000001
>>> b = 10000000000000000.0+0.0j
>>> c = 9999999999999999
>>> a==b
True
>>> b==c
True
>>> a==c
False

Is this any different?

(Reply to this) (Thread)(Expand)

	Re: Python zestyping 2005-06-13 04:59 pm UTC (link)
	Nice catch! I would consider that a bug. I think this would be much less likely to bite you than what PHP does, but it's still a bug. (Reply to this) (Parent)(Thread)(Expand)

Re: Python -

r6, 2005-06-13 07:29 pm UTC (Expand)

Re: Python -

zestyping, 2005-06-13 08:07 pm UTC (Expand)

Re: Python -

r6, 2005-06-13 08:46 pm UTC (Expand)

Re: Python -

zestyping, 2005-06-15 12:41 am UTC (Expand)

Re: Python -

regebro.wordpress.com, 2008-03-21 10:06 am UTC (Expand)

Mathematica

r6
2005-08-18 03:00 pm UTC (link)

I just started reading section 9 of A Review of Mathematica.

In[1]:= p=314159265358979323;
        q=314159265358979323.;
        r=314159265358979323.0000000000000000000;
        s=p+0.00000000000000000000;

In[2]:= {Tan[s],N[Tan[p]],Tan[q],Tan[r]}

Out[2]= {1.59981, 1.59981, ComplexInfinity, -1.1297926523089085443}

In[3]:= {p==q, q==r, r==s, r==p}

Out[3]= {True, True, True, True}

(Reply to this)

(Anonymous)
2005-09-05 07:14 am UTC (link)

In fairness, it is a SCRIPTING language, not a programming language, because it was made to solve a specific problem ie. web problems (and probably because it isn't very "politically correct").
Furthermore, the PHP manual already explained that behavior, so i don't see what's the fuss...
Maybe it shouldn't be taught, but it sure as hell is easy to learn (especially when you need something up and running right away).

(Reply to this) (Thread)(Expand)

eevee
2007-12-11 09:57 pm UTC (link)

Scripting languages are programming languages. The distinction is arbitrary, and there is no difference in capability; all are Turing-complete. Perl, Ruby, and Python are all very mature and powerful languages. I'm sorry that PHP has tainted your view of them all.

The PHP manual could explain that 2 + 2 is actually 5, but that wouldn't make the behavior any less absolutely stupid.

What makes PHP easy to learn? That you can copy-paste solutions for any introductory programming task from Google or the manual? What do you do after that?

(Reply to this) (Parent)(Thread)(Expand)

(no subject) - (Anonymous), 2007-12-12 12:36 am UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 01:29 am UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 01:39 am UTC (Expand)

(no subject) -

zestyping, 2007-12-12 02:29 am UTC (Expand)

(no subject) - (Anonymous), 2007-12-12 04:50 am UTC (Expand)

(no subject) - (Anonymous), 2007-12-17 01:17 pm UTC (Expand)

(no subject) -

eevee, 2007-12-12 04:53 pm UTC (Expand)

(no subject) -

marissacovyg, 2008-07-16 01:51 am UTC (Expand)

	or why reading /should/ be taught ... sinf 2007-12-11 10:43 pm UTC (link)
	Isn't this more an example of why programmers should learn the very basics of a language before using it? How comparison works in PHP is very well described in the documentation: http://www.php.net/manual/en/language.operators.comparison.php (Reply to this) (Thread)(Expand)

	Re: or why reading /should/ be taught ... arthurdenture 2007-12-12 01:13 am UTC (link)
	Yes, and the comparison tables linked from there -- http://www.php.net/manual/en/types.comparisons.php are another great example of why you shouldn't use PHP. (Reply to this) (Parent)

Re: or why reading /should/ be taught ... -

eevee, 2007-12-12 04:18 pm UTC (Expand)

Re: or why reading /should/ be taught ... - (Anonymous), 2008-01-15 01:38 am UTC (Expand)

	Type casting (Anonymous) 2007-12-11 10:57 pm UTC (link)
	I like this one also: <?php $a = "string"; var_dump((bool) $a); var_dump((int) $a); var_dump((int) (bool) $a); ?> Output: bool(true) int(0) int(1) I remember having been bitten by if ($foo == 0) { .. I remember it well.. (Reply to this) (Thread)

	Re: Type casting (Anonymous) 2007-12-12 12:01 am UTC (link)
	> var_dump((bool) $a); >>> bool(true) Sure, any non-empty string would return true when cast to boolean. > var_dump((bool) $a); >>> bool(true) Sure, it doesn't look like a valid number to me. > var_dump((int) (bool) $a); >>> int(1) Sure, it's first cast to bool (true), which is then cast to int (true == 1). (Reply to this) (Parent)

garthnak
2007-12-11 11:02 pm UTC (link)

$ cat equality.php
<?php

$a = 0;
$b = "eggs";
$c = "spam";

print ($a === $b) ? "a === b\n" : "a !== b\n";
print ($b === $c) ? "b === c\n" : "b !== c\n";
print ($a === $c) ? "a === c\n" : "a !== c\n";
print ($a === $d) ? "a === d\n" : "a !== d\n";
print ($b === $d) ? "b === d\n" : "b !== d\n";
print ($c === $d) ? "c === d\n" : "c !== d\n";

?>

$ php equality.php
a !== b
b !== c
a !== c
PHP Notice: Undefined variable: d in /home/garthnak/equality.php on line 10
a !== d
PHP Notice: Undefined variable: d in /home/garthnak/equality.php on line 11
b !== d
PHP Notice: Undefined variable: d in /home/garthnak/equality.php on line 12
c !== d

$

(Reply to this)

	beverlyhillscop 2007-12-11 11:30 pm UTC (link)
	This post would be more aptly titled "Why I should learn PHP." (Reply to this) (Thread)

	Nice (Anonymous) 2007-12-12 02:33 am UTC (link)
	You hit the nail on the head, my friend. While I don't particularly like PHP, don't program in the language until you first learn it. (Reply to this) (Parent)(Thread)(Expand)

Programming languages aren't all the same. - (Anonymous), 2007-12-12 09:25 am UTC (Expand)

Re: Programming languages aren't all the same. -

zestyping, 2007-12-12 11:44 am UTC (Expand)

Re: Programming languages aren't all the same. - (Anonymous), 2008-01-01 12:35 pm UTC (Expand)

Re: Programming languages aren't all the same. - (Anonymous), 2008-02-02 08:34 pm UTC (Expand)

Re: Programming languages aren't all the same. -

eevee, 2007-12-12 04:38 pm UTC (Expand)

	Many more reasons why PHP should not be (Anonymous) 2007-12-12 03:35 am UTC (link)
	are well explained in this post: http://toykeeper.net/soapbox/php_problems/ (Reply to this)

GNU Emacs

vityok
2007-12-12 10:29 am UTC (link)

Oh my, GNU Emacs handles this case much more elegantly:

(setq var-a 10)
(setq var-b "eggs")
(setq var-c "spam")

(eq var-a var-b) ; nil
(eq var-b var-c) ; nil
(eq var-a var-c) ; nil
;; var-d is a void variable, does not work
(eq var-a var-d)
(eq var-b var-d)
(eq var-c var-d)

(Reply to this)

hotgiraffe
2007-12-12 01:46 pm UTC (link)

actually, Java (starting from 1.5) shows just such a non-transitive behaviour when auto-unboxing is involved

public class A {

  public static void main(String[] args) {
    int a = 3;
    Integer b = new Integer(3);
    Integer c = new Integer(3);

    System.out.println(a == b ? "a == b" : "a != b");
    System.out.println(a == c ? "a == c" : "a != c");
    System.out.println(b == c ? "b == c" : "b != c");
  }
}

prints

a == b
a == c
b != c

(Reply to this) (Thread)(Expand)

	zestyping 2007-12-12 08:39 pm UTC (link)
	Yup. It's a bug. (Reply to this) (Parent)

(no subject) -

naikrovek, 2008-01-02 08:35 pm UTC (Expand)

(no subject) -

hotgiraffe, 2008-01-03 01:06 pm UTC (Expand)

	eevee 2007-12-12 05:04 pm UTC (link)
	So.. I have to ask, was this dugg or something? Someone linked me here and it took me a while to notice the 2005 date. (Reply to this) (Thread)(Expand)

	javascript (Anonymous) 2007-12-12 05:51 pm UTC (link)
	for something like this in javascript see: http://laurens.vd.oever.nl/weblog/ontheedge/boolean/boolean.html (Reply to this) (Parent)

My Fault -

roconnor.myopenid.com, 2007-12-12 08:27 pm UTC (Expand)

(no subject) - (Anonymous), 2007-12-14 12:38 pm UTC (Expand)

	javascript (Anonymous) 2007-12-12 05:52 pm UTC (link)
	for something like this in javascript see: http://laurens.vd.oever.nl/weblog/ontheedge/boolean/boolean.html (Reply to this)

	Another weird scenario in PHP (Anonymous) 2007-12-12 08:35 pm UTC (link)
	I recently posted a blog entry about C# vs PHP and gave an example in PHP as to how it adds numbers and strings. You can find it here. http://keithelder.net/blog/archive/2007/12/05/Using-Regular-Expressions-in-C-vs-PHP.aspx As I state in the article, when I taught PHP, no one ever could predict the outcome of that example. It just isn't logical. (Reply to this)

It's the truth table.
(Anonymous)
2007-12-13 05:08 am UTC (link)

This is all 'perfectly reasonable' according to PHP's truth table.

http://www.php.net/manual/en/types.comparisons.php

When I used PHP I hated this. Because developers would use PHP's truth junk in conditionals and if you couldn't memorise it you'd have to go look it up.

Also if you didn't memorise it you'd get unexpected errors sometimes when people'd put values like 0 into forms.

I work almost exclusively in Ruby now, and I love Ruby's discernment of truth: Anything that is nil or false is false, everything else is true. Easy to remember.

I also like Python, but I can't remember what it's truth table was, I recall it was also quite simple :)

Ryan.
http://yeahnah.org

(Reply to this)

	sloot 2007-12-14 12:33 pm UTC (link)
	I agree with you.. up to the === operator. I assume the original posting was written before the === operator was released. (Reply to this)

	Wrong operator (Anonymous) 2008-01-01 01:49 pm UTC (link)
	That's misleading, because you're using the wrong operators -- retry your test using the proper '===' and '!==' operators, and you'll see the correct result. (Reply to this)

	Your post is sloppy (Anonymous) 2008-01-01 04:44 pm UTC (link)
	Seriously, this post is plain sloppy. If you don't know the difference in PHP between the '==' and '===' operators then you shouldn't be making sweeping arguments for or against the language. See John Lim's more detailed retort: http://phplens.com/phpeverywhere/?q=node/view/244 (Reply to this)

	(Anonymous) 2008-01-01 06:04 pm UTC (link)
	I don't understand something, so it shouldn't exist! Waaah! If you're just starting in computer science you're in for a lifetime of disappointment son. (Reply to this)

(101 comments) - (Post a new comment)

Page 1 of 2
<<	[1] [2]	>>

Username:		Create an Account Forgot your login or password? Login w/ OpenID
Password:
	Remember Me
	English • Español • Deutsch • Русский…

About

Help

Get Involved

Legal

Store

LJ Labs