Question

I’m writing some explicit operators to convert database model types to my domain model. Like so (simplified example):

public static explicit operator DomainModel.Role(Role roleEntity)
{
   DomainModel.Role role = new DomainModel.Role
   {
      RoleId = roleEntity.RoleId,
      Name = roleEntity.Name
   };

   return role;
}

However it’s possible that the roleEntity parameter is null. Most of times in the .net framework an explicit cast of a null instance results in an exception. Like so:

user.Role = (DomainModel.Role)_userRepository.GetRole(user); // Would normally results in a NullReferenceException

But if the explicit operator would be adjusted, the above would function as expected:

public static explicit operator DomainModel.Role(Role roleEntity)
{
   DomainModel.Role role = roleEntity == null ? null : new DomainModel.Role
   {
      RoleId = roleEntity.RoleId,
      Name = roleEntity.Name
   };

   return role;
}

Question:

• Is it logical to create such explicit operators?

Answer 1

To the title-question: An explicit operator is allowed to throw (while an implicit operator should not).

But whether a null is a valid reason to do so is a design decision, I would think not.

Consider:

object x = null;
string t = (string)x;

which does not throw.