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Date: Sat, 28 Mar 2020 11:10:03 +0000
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Reply-To: =?utf-8?q?Terje=20Sletteb=c3=b8?= <terje.slettebo@sandefjordbredband.net>
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Subject: Function and operator overloading
From: terje.slettebo@sandefjordbredband.net (=?utf-8?q?Terje=20Sletteb=c3=b8?=)

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Hi.

Please excuse me if this has been discussed to death earlier. I've tried
to search for it, but I've come up empty:=20
https://www.php.net/results.php?
q=3Dfunction+overloading&l=3Den&p=3Dall

The recent discussion on operator overloading has highlighted the
relationship between function overloading and operator overloading, and
how having support for the former may help provide the latter.

For those with experience with C++, function and operator overloading
works the same way, and the only difference is that operator overloading
is defined as a function of the form "operator+(...)", i.e. "operator"
followed by the operator itself.

I know that C++'s system for overloading is very complex (because it has
something called partial ordering of functions, and it also includes
templates/generics).

Nevertheless, I think it could be possible to implement a subset in PHP,
without all the complexity, and in this way provide a cleaner way of
implementing either kind of overloading, and avoiding the "closed set" /
library interaction issues mentioned in the other thread.

What I have in mind is to let the parameter types of a function become
part of the function name, something like this:

// Function overloads

function add(Money $a, Money $b): Money
{
   ...
}

function add(Matrix $a, Matrix $b): Matrix
{
   ...
}

// Operator overloads

function operator+(Money $a, Money $b): Money
{
   ...
}

function operator*(Money $a, Percentage $b); Money
{
   ...
}

function operator*(Matrix $a, Matrix $b): Matrix
{
   ...
}

Use:

$m1 =3D new Money(100);
$m2 =3D new Money(200);
$p =3D new Percentage(10);

$result =3D $m1 + $m2; // Money(300)

$result =3D $m1 * $p; Money(10)

I realise that including the parameter types as part of the (internal)
name of a function is a major departure from the way PHP works today.

However, if we are to grow PHP into the future, and continue to provide
clean ways of expressing things, then maybe we should re-examine such
fundamental things, where a clean interface and simplicity for the
developer is more important than implementation complexity.

Regards,

Terje
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