Add hook mechanism for result

[wenerme]

For every result I want to execute a postconstruct method

func PostConstruct(v interface{}, ctx context.Context) error {
	c, ok := v.(interface {
		PostConstruct(ctx context.Context) error
	})
	if ok {
		return c.PostConstruct(ctx)
	}
	return nil
}

Because I construct resolver simply by &myResolver{value:v}, but when I want to use exists resolver

type myResolver struct{
    v MyValue
    *CommonResolver
}

I need to init the *CommonResolver after this resolver has created. So, I need a hook to postconstruct after every field has resolved.

One of my init look like this

func (self *myResolver) PostConstruct(ctx context.Context)(err error) {
	if self.ctx == nil {
		self.ctx,err = MustMyContextFrom(ctx)
	}
	if self.CommonResolver == nil {
		self.CommonResolver = &CommonResolver{Value: self.item}
	}
	return
}