PHP5: type hinting with optional arguments

Rob Long

Hey,

I've just noticed a somewhat annoying feature with PHP5 type hinting.

You cannot hint types on optional arguments like this:

class MyClass
{
function someFunc(Type1 $arg1, Type2 $arg2 = new Type2()) { }

//or
function someFunc(Type1 $arg1, Type2 $arg2 = null) { }

//or
function someFunc(Type1 $arg1, Type2 $arg2 = Type2::getInstance()) { }
}

In fact, there doesn't seem to be any way to do this. I guess you could do
something with global variables, but no thanks....

Any ideas??

Rob Long.

Jul 17 '05 #1

Berislav Lopac

Rob Long wrote:

Hey,

I've just noticed a somewhat annoying feature with PHP5 type hinting.

You cannot hint types on optional arguments like this:

class MyClass
{
function someFunc(Type1 $arg1, Type2 $arg2 = new Type2()) { }

//or
function someFunc(Type1 $arg1, Type2 $arg2 = null) { }

//or
function someFunc(Type1 $arg1, Type2 $arg2 = Type2::getInstance()) { }
}

In fact, there doesn't seem to be any way to do this. I guess you
could do something with global variables, but no thanks....

Any ideas??

IMO, it's only logical. Optional arguments need to have a literal value as
the default, and in your examples above only null is a literal value; others
are expressions, which are not allowed in optional argumetn definitions.

Remember that PHP is dynamically typed language; there is nothing preventing
you from:

function Function($obj = null) {}

$object = new Class();

Function($object);

Berislav
--
If the Internet is a Marx Brothers movie, and Web, e-mail, and IRC are
Groucho, Chico, and Harpo, then Usenet is Zeppo.

Jul 17 '05 #2

Rob Long

"Berislav Lopac" <be************@dimedia.hr> wrote in message news:<cajoc5

IMO, it's only logical. Optional arguments need to have a literal value as
the default, and in your examples above only null is a literal value; others
are expressions, which are not allowed in optional argumetn definitions.

Remember that PHP is dynamically typed language; there is nothing preventing
you from:

function Function($obj = null) {}

$object = new Class();

Function($object);

Berislav

I disagree. The whole point of type hiniting is to provide a runtime
contract between the calling code and the called function. Why is it
logical that mandatory arguments should be hinted and optional
arguments should not? Especially considering the fact that there is no
function overloading in PHP.

I realise that PHP is dynamically typed, which is precisely why type
hinting was implemented - in order to reduce errors. Of course there
are workarounds, such as:

Class MyClass
{
function someFunc(Type1 $arg1, $arg2 = null)
{
if (!is_null($arg2) && !($arg2 instanceof Type2))
{
throw new IllegalArgumentException();
}
}
}

But we may as well do away with type hinting altogther and provide
runtime type-checking with the is_a() functions.

Rob Long.

Jul 17 '05 #3

Phil Roberts

bo******@gmx.net (Rob Long) emerged reluctantly from the curtain
and staggered drunkenly up to the mic. In a cracked and slurred
voice he muttered:

I disagree. The whole point of type hiniting is to provide a
runtime contract between the calling code and the called
function. Why is it logical that mandatory arguments should be
hinted and optional arguments should not? Especially considering
the fact that there is no function overloading in PHP.

Type hinting in PHP5 only applies to objects anyway, and with the new
object model all objects are passed by reference. Default parameters
were only ever available to variables passed by value.

--
Phil Roberts | Without me its just aweso. | http://www.flatnet.net/

"I don't hate MurphyInOhio, I pity the fool!"
- Mr T.

Jul 17 '05 #4

Rob Long

Phil Roberts <ph*****@HOLYflatnetSHIT.net> wrote in message news:<Xn*************************@216.196.97.132>. ..

Type hinting in PHP5 only applies to objects anyway, and with the new
object model all objects are passed by reference. Default parameters
were only ever available to variables passed by value.

OK, I think I may have to further explain the point of my question.
Answer these simple questions:

1. Is there function overloading in PHP?
2. Why does PHP not need function overloading, like languages such as
Java do?

When you've done that you come to the conclusion that the workaround
for having no function overloading is default arguments. So far so
good...

...Until type hinting comes along, which, IMO, is a partially
implemented feature if it doesn't allow for hinting on optional
arguments. I think people are getting bogged down in syntax here...
saying things like "you can't have expressions in arguemnts
definitions." I really couldn't care less about having expressions in
argument defintions...

function someFunct(Type1 $arg1, Type2 $arg2 = new Type2()) { }

or

function someFunct(Type1 $arg1, Type2 $arg2 = Type2::getInstance()) {
}

....IS ugly, which is why there should be a new syntax for optional
(hinted) arguments in PHP5, such as:

function someFunc(Type1 $arg1, ? Type2 $arg2)

or

function someFunc(Type1 $arg1, [Type2 $arg2], [Type3 $arg3]) etc
etc...

Just to say "well that's the way it works" isn't very helpful, nor is
it informative.

Jul 17 '05 #5

Phil Roberts

bo******@gmx.net (Rob Long) emerged reluctantly from the curtain
and staggered drunkenly up to the mic. In a cracked and slurred
voice he muttered:

1. Is there function overloading in PHP?
2. Why does PHP not need function overloading, like languages
such as Java do?

1. No
2. Because there are numerous workarounds. I've never had any need
for it myself...

--
Phil Roberts | Without me its just aweso. | http://www.flatnet.net/

"I don't hate MurphyInOhio, I pity the fool!"
- Mr T.

Jul 17 '05 #6

Xellos[FSO]

> 1. No

2. Because there are numerous workarounds. I've never had any need
for it myself...

To Phil: You are completely missing Rob's point. And those two questions
were rhetorical. Your teacher - back in HS - must have explained those,
while you were sleeping...

To Rob: since type hinting in PHP only applies to objects and default
values can only be basic data types, so there is no practical use of
hinting for default values.

The standard situation:

function someFunc($objectoOfTypeCoolExpected = NULL) {}
or if you wish:
function someFunc($objectoOfTypeCoolExpected = 'There was no object
given') {}

In both cases you should hint two types: type NULL or string in addition
to object type 'Cool'. And as we know it - we can't hint basic types...
(which is bad IMO)

The other way of doing this would be:

function someFunc($objectoOfTypeCoolExpected =
$GLOBALS['defaultCoolObjectToUse']) {}

Now both situations (default value and given parameter) could be of the
same type and thus be hinted with one object type. The thing is that this
is a bad coding example, as you shouldn't really expect that there will be
some variable declared in the global scope, when the function is called. I
know you can code this like that, but you shouldn't.

Perfect solution would be:

function someFunc($objectoOfTypeCoolExpected = new Cool()) {}

This way you could hint the type and expect proper results. Too bad
dynamic default parameters aren't allowed.

Discuss.

Kind regards,
Adam Wróbel
aka Xellos[FSO]
--
Experience is what you get when you don't read directions.

Mail: xe****@xellos.info
WWW: http://xellos.info
GG: 2369996

Jul 17 '05 #7

Rob Long

> To Rob: since type hinting in PHP only applies to objects and default

values can only be basic data types, so there is no practical use of
hinting for default values.
Well, you CAN pass objects as default values, you just can't hint them.
If you provide explicit checking combined with the excpetion mechanism
then you can achieve the same effect as hinting, but it's so much more
hassle and error-prone!
The standard situation:

function someFunc($objectoOfTypeCoolExpected = NULL) {}
or if you wish:
function someFunc($objectoOfTypeCoolExpected = 'There was no object
given') {}

In both cases you should hint two types: type NULL or string in addition
to object type 'Cool'. And as we know it - we can't hint basic types...
(which is bad IMO)
Yeah. You can use the checking I describe above to provide your own hinting,
even on basic types, but you've still got to do this and it requires effort
and discipline on the part of the developer.

Compare

function someFunc(int $x, int $y, MyType $mt, Type2 $at = new Type2()) {
//...
}

with

function someFunc($x, $y, MyType $mt, $at = null) {
if (!is_integer($x))
{
throw new IllegalArgumentException("First argument must be of " .
type: integer");
}

if (!is_integer($y))
{
throw new IllegalArgumentException("Second argument must be of " .
type: integer");
}

if (!is_null($at))
{
if (!($at instanceof AnotherType))
{
throw new IllegalArgumentException("[Optional] fourth argument " .
"must be of type: AnotherType");
}
}
else $at = new AnotherType();

//...
}

Bloody annoying if you ask me!
The other way of doing this would be:

function someFunc($objectoOfTypeCoolExpected =
$GLOBALS['defaultCoolObjectToUse']) {}
Most developers who are THAT concerned about hinting would shy away
from globals immediately. This isn't even a solution for me...
Perfect solution would be:

function someFunc($objectoOfTypeCoolExpected = new Cool()) {}
Totally.

This way you could hint the type and expect proper results. Too bad
dynamic default parameters aren't allowed.

Regards,
Rob Long.

Jul 17 '05 #8

Xellos[FSO]

So we agree that this thing is kind of incomplete and really only useful
to those parameters that are objects AND do not have default value. That's
a BIG limitation for me, but I won't say that I can't live with it...

Kind regards,
Adam Wróbel
aka Xellos[FSO]
--
Experience is what you get when you don't read directions.

Mail: xe****@xellos.info
WWW: http://xellos.info
GG: 2369996

Jul 17 '05 #9

Rob Long

"Xellos[FSO]" <xe*******@go2.pl> wrote in message news:<opr9otmgfivloyey@devsdesk>...

So we agree that this thing is kind of incomplete and really only useful
to those parameters that are objects AND do not have default value. That's
a BIG limitation for me, but I won't say that I can't live with it...

Me neither; I love PHP! I mean, until now I've been working around
member scope, interfaces, static members etc etc, so this one I can
definitely live with.... it's just a shame that it's only partially
implemented.

Jul 17 '05 #10