4.x - Eliminate a duplicate code via HOF

[mapogolions]

• reduce responsibility of some methods
• move duplicate code into a separate private function
• add more strict type hinting

[coveralls]

Coverage remained the same at 100.0% when pulling 772c5ad on mapogolions:maintenance/duplicate-code into a139440 on slimphp:4.x.

[l0gicgate]

It looks tidier for sure. @adriansuter please review before I merge.

[adriansuter]

Wonderful work.

One minor change request and one question: Do you think it would make sense to take the Closures out of the resolveRoute and resolveMiddleware methods? Otherwise php has to create the Closure over and over again, whenever the middleware or route get resolved.

For example:

    protected function routePredicate($it): bool
    {
        return $it instanceof RequestHandlerInterface;
    }

    protected function middlewarePredicate($it): bool
    {
        return $it instanceof MiddlewareInterface;
    }

    /**
     * {@inheritdoc}
     */
    public function resolveRoute($toResolve): callable
    {
        return $this->resolveByPredicate($toResolve, [$this, 'routePredicate'], 'handle');
    }

    /**
     * {@inheritdoc}
     */
    public function resolveMiddleware($toResolve): callable
    {
        return $this->resolveByPredicate($toResolve, [$this, 'middlewarePredicate'], 'process');
    }

Of course the signature of resolveByPredicate would have to be adapted.

[mapogolions]

@adriansuter we were able to remove duplicate code, thanks to ideas from FP. In particular - higher order function. As you know, a function is treated like a Fist Class Citizen (as any variable). Creating a local function with every function call is a common practice. Other languages have more concise syntax, like it.map(x => x + 1)

[adriansuter]

Of course. I am open to any solution. Other languages do not only have more concise syntax, but they often have compilers and optimizers too. I am not sure, whether PHP does recognize the Closure to be the same during a second call. And I don't know if there would be any negative performance impact. But I can imagine, there is. Not sure, how big though.

Nevertheless, writing the Closures in the two methods would have the advantage, that everything "needed" is written inside the methods. So that might be better for maintainability.

As I said, I don't actually have a strong opinion for one or the other solution. Both have their advantages and disadvantages.

[mapogolions]

Since I already made a commit that removes predicates from methods. Let's it be as it is. I think this is not so fundamental.