As explained under 'read more', it's because 'test' will be cast to a number for comparison. Since 'test' isn't a number, it becomes 0, which is equivalent.

Which is, of course, a deeply broken way to handle the situation. If multi-type comparisons have to be supported at all, at least one ought to cast the narrower type to the wider one! In this case, the int argument ought to be cast to string, because all ints can be uniquely represented as a string, but not the other way around.

As it stands, PHP's equality operator is not an equivalence relation because it's not transitive. This is deeply unintuitive and logic-defying.

== is not the equality operator. === is the equality operator.

== is the type coerce/cast and then compare operator.

I agree with you about the way strings get converted to int instead of the other way around. I believe this is a backwards compatibility issue, and if they could change it they would, but it's too late.

It's also because of 1 == "01" would be false otherwise. And if you think "01" is strange you forget that all input to a php program comes from web forms, and is always a string.

in javascript:

1 == '01' --> true

0 == 'x' --> false

1 == '1' --> true

true == 'asdf' --> false

'-2' == 2 --> true

'-2' == 0 --> false

Seems like in javascript, the coercing is much more sane. In php, all of the above statements would end up true.

Javascript is not totally sane:

  '\t\r\n' == 0 --> true

And not transitive:

  "false" == "0" --> false
  "0" == 0 --> true
  0 == false --> true
  false == "false" --> false

It's basically impossible to make a loosely typed equality perfect.

PHP is much more strict about the rules used when doing the comparison, javascript is more loose. It tries to guess.

When comparing a string to a number, if the string looks like a number it's converted to one. But if it doesn't, then instead the number get converted to a string.

This works well most of the time - but not always, since it can surprise you. PHP is more strict, so it doesn't work as often, but it fails more consistently, so it's easier to find the problem.

Another example:

  "1" == "01" --> false
  "01" == 1 --> true
  1 == "1" --> true

I don't have a PHP runtime in front of me, but IIRC the first one on your list and the last 2 will evaluate false in php

The funny thing is that in Javascript:

12 == parseInt('012')

returns false. :)

A leading zero usually means 'this number is octal', so parseInt returns 10. Not very intuitive notation, however.

I really would find this "deeply unintuitive" if I decided to try PHP with only intellisense as a reference. But by their very definition a language's idioms are not obvious. And this isn't my first rodeo, so I'd know that. And I'd read a little--just a little--before i jumped in.

Concepts and algorithms are universal. Operators and keywords are not.

Luckily, this is such a common need when learning a language that this information is kept all together in a tidy tabular way.

Because without it, I'd probably whip up an index.php and write something like print 'Welcome, ' + user.firstName;, get frustrated by parse errors, then by runtime errors, then write some impassioned comment about how deeply unintuitive it is to require prefixed variables and how using a dot for concatenation instead of a plus sign or ampersand is simply logic defying.

And that same table that explains concatenation and scope resolution is also going to give me a simple treatment on the == and === operators in this weakly typed language.

PHP is not an elegant language and given the choice, I'd nearly always prefer to be writing something else. But I took my time to respond to this because there's enough wrong with PHP that we don't need to resort to hyperbole to bash it.

I mostly agree, except that I don't think any treatment explaining

  NULL != "0" == false == NULL == 0 == "false" == true

is going to be simple.

Sure it is:

To avoid implicit type coercion, use the identity operators === and !==.

Of course, the code you posted doesn't parse without adding parens. And when you do, it becomes much more obvious what it's doing and why.

Sorry, I meant that as a bunch of compares that are mutually inconsistent, not one big expression. And "don't use ==" isn't really a solution until you persuade the runtime and every major library author to stop using it.

I don't get your point. Nobody has said "don't use equality." Equality is the right choice nearly all the time.

I've worked on some very large web apps (mostly C#, Python and PHP) and I can't recall ever really being foiled by php's implicit casting.

Just out of genuine curiousity, can you share an example where this caused a problem that you had to debug?

And if php implicit casting did somehow cause you problems, surely it was fixed by changing it from equality to identity?

So in summary... this could potentially cause a bug, but probably not, and if it does, it would be a consistent bug, and it would be fixed by a single keystroke.

Why, again, are we talking about this?

That isn't legal PHP.