SubstituteImplicitBindings.php

<?php

namespace App\Http\Middleware;

use Closure;
use ReflectionMethod;
use ReflectionFunction;
use Illuminate\Database\Eloquent\Model;

class SubstituteImplicitBindings
{
    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        $routeInfo = $request->route();

        $parameters = $routeInfo[2];

        $signatureParameters = $this->signatureParameters($routeInfo[1], Model::class);

        foreach ($signatureParameters as $parameter) {
            $class = $parameter->getClass();

            if (array_key_exists($parameter->name, $parameters)) {
                $method = $parameter->isDefaultValueAvailable() ? 'first' : 'firstOrFail';

                $model = $class->newInstance();

                $routeInfo[2][$parameter->name] = $model->where(
                    $model->getRouteKeyName(), $parameters[$parameter->name]
                )->{$method}();
            }
        }

        $request->setRouteResolver(function () use ($routeInfo) {
            return $routeInfo;
        });

        return $next($request);
    }

    private function signatureParameters($action, $subClass = null)
    {
        if (isset($action['uses'])) {
            list($class, $method) = explode('@', $action['uses']);

            $parameters = (new ReflectionMethod($class, $method))->getParameters();
        } else {
            $parameters = (new ReflectionFunction($action[0]))->getParameters();
        }

        return is_null($subClass) ? $parameters : array_filter($parameters, function ($p) use ($subClass) {
            return $p->getClass() && $p->getClass()->isSubclassOf($subClass);
        });
    }
}

Check out this package Lumen Route Binding

It requires :

php >= 5.4.0
Lumen 5.*

It supports Explicit binding :

$binder->bind('user', 'App\User');

And Implicit binding :

$binder->implicitBind('App\Models');

And Composite binding : (bind more than one wildcard together, In situations like posts\{post}\comments\{comment} you will be able to bind it to a callable that will resolve the Post and the Comment related to the post)

$binder->compositeBind(['post', 'comment'], function($postKey, $commentKey) {
    $post = \App\Post::findOrFail($postKey);
    $comment = $post->comments()->findOrFail($commentKey);

    return [$post, $comment];
});

Also can work with other classes like Repositories :

// Add a suffix to the class name
$binder->implicitBind('App\Repositories', '', 'Repository');

Can use a custom method on the repository :

// Use a custom method on the class
$binder->implicitBind('App\Repositories', '', 'Repository', 'findForRoute');

Where in the repository class you can do :

public function findForRoute($val)
{
    return $this->model->where('slug', $val)->firstOrFail();
}