Type resolver concept for https://github.com/digiaonline/graphql-php

schema.graphqls

interface Vehicle {
  maxSpeed: Int
}

type Airplane implements Vehicle {
  maxSpeed: Int
  wingspan: Int
}

type Car implements Vehicle {
  maxSpeed: Int
  licensePlate: String
}

VehicleResolver.php

class VehicleResolver extends AbstractResolver
{
    public function resolveFoo()
    {
        return 'foo';
    }

    public function resolveType($rootValue, $contextValues, $info)
    {
        if ($rootValue instanceof Airplane) {
            return 'Airplane';
        }

        if ($rootValue instanceof Car) {
            return 'Car';
        }

        return null;
    }
}