code: func (c *ExampleService) FindUser(ctx context.Context, filter platform.UserFilter) (*platform.User, error) {
  	if filter.ID != nil {
  		u, err := c.FindUserByID(ctx, *filter.ID)
  		if err != nil {
  			return nil, &platform.Error{
  				Op:  "kv/" + platform.OpFindUser,
  				Err: err,
  			}
  		}
  		return u, nil
  	}
  
  	if filter.Name != nil {
  		return c.FindUserByName(ctx, *filter.Name)
  	}
  
  	filterFn := filterExamplesFn(filter)
  
  	var u *platform.User
  	err := c.kv.View(func(tx Tx) error {
  		return forEachExample(ctx, tx, func(usr *platform.User) bool {
  			if filterFn(usr) {
  				u = usr
  				return false
  			}
  			return true
  		})
  	})
  
  	if err != nil {
  		return nil, err
  	}
  
  	if u == nil {
  		return nil, &platform.Error{
  			Code: platform.ENotFound,
  			Msg:  "user not found",
  		}
  	}
  
  	return u, nil
  }
docs: // FindUser retrives a example using an arbitrary example filter.
  // Filters using ID, or Name should be efficient.
  // Other filters will do a linear scan across examples until it finds a match.