On 03/21/2016 03:04 PM, Facundo Martinez Correa wrote:
So I want to "return a NULL". I want to express uncertainty, a
nonexistence. But I want to express that I will return something. And I
want to have this NULL checking at interpretation time. I want everything,
and none of the drawbacks. As we say here in Argentina, I want the bread
and the cake. What can we do to have it? After a bit of thought the Maybe
monad came to me.
My experience in Haskell reminded me of this. To have a structure than
represents uncertainty, is the best way to take away the responsibility
from NULL. To express it in no other way. But my experience in Java has
taught me that Optional of something is not a good way to tackle the
problem. I still have to check if my Optional isEmpty. I still have to
check for null. That is because Java has that type erasure after
compilation time that doesn't allow me to play nice with polymorphism. But
maybe PHP can. Maybe PHP will give me the polymorphism at execution time to
discern an empty Maybe from the one that is not. So I don't have to check
for null ever again in my life. So my code can be free of nulls. So I can
express uncertainty and nonexistance, while I return a User from my
repository.
I hope someone would like this idea. I'm also open to suggestions.
Kind regards
Facundo Martínez
First of all, let me confess that I absolutely love monad (or composite)
types, and I greatly prefer a Maybe over something that may or may not
be null. There's a slight problem however, and something that will not
be easy to get around: a lack of generics.
This is an issue with wrapper types in general in PHP, where you want to
wrap an object in some other type. You lose type safety on the inner
object, and so I tend to look for a more type-safe solution in PHP.
There is already a generics RFC out there
(https://wiki.php.net/rfc/generics) but implementing it won't be trivial.
Implementing (or defining) a good Maybe type also depends on better
composite/enum types (https://wiki.php.net/rfc/enum is drafted, but
doesn't support what we need). The classical definition would be
(hypothetical PHP syntax):
enum Maybe<T>
{
Some {
public function __construct(T $value);
public function isSome(): bool {
return true;
}
public function into(): T {
return $this->value;
}
},
None {
public function isSome(): bool {
return false;
}
public function into(): T {
throw new Error();
}
}
}
Such a definition depends on two different things we don't have right
now in PHP. Maybe there's a simpler way, but hopefully you have a better
alternative?
--
Stephen
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