laravel route where regex code example

Example: comment = Comment::find($this->route('comment')); in laravel

Schema::create('comments', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('user_id')->unsigned();
            $table->foreign('user_id')->references('id')->on('users')->onCascade('update')->onDelete('cascade');
            $table->integer('post_id')->unsigned();
            $table->foreign('post_id')->references('id')->on('users')->onCascade('update')->onDelete('cascade');
            $table->text('comment');
            $table->timestamps();
            $table->rememberToken();
        });