Force implementation of default constructor

Question

Possible Duplicate:
Interface defining a constructor signature?

I have a mixed hierarchy of classes and interfaces.

For using serialisation I need a default constructor present in each class. I would really aprreciate if the compiler could tell me that a default constructor is missing somewhere in the hierarchy. (seeing the problem at compile time, not in the later tests)

What I would like to have could be some markup or attribute, but I could not find anything.

Something like:

[ForceDefaultConstructor]
interface IVeryQuickSerializable
{   
    Serialize();
    Deserialize();
}

would be great!

But anything like that is very appreciated.

There is a limitation: I cannot change the Serialisation. Making it generic would solve the problem, but I do not have the source. Writing a wrapper might do the job, but it will have a loophole for objects deriving from the toplevel Serialisation interface (which may not be altered).

Assuming that everything descends from `Object`, it already has a default constructor. Perhaps I'm missing something here? — 3Dave, Jun 20 '12 at 18:53
@DavidLively constructors aren't inherited; `class Foo { public Foo(int i) {...}` does **not** have a parameterless constructor — Marc Gravell, Jun 20 '12 at 18:53
I'd like to suggest reading this: http://social.msdn.microsoft.com/forums/en-US/csharplanguage/thread/f6364918-fc7f-4153-b020-6ce14b34820c Although they provide something like a solution, that uses generics. — nxu, Jun 20 '12 at 18:56
already saw that one, but there he wants some parameters, i especially want >no< parameters. — Mare Infinitus, Jun 20 '12 at 18:57
@MarcGravell constructors for base classes *are* called (inherited) when you instantiate a child class. You only need to declare a constructor `Foo() {}' when you've added a constructor that requires parameters. — 3Dave, Jun 20 '12 at 19:06
The problem is, that i cannot construct a Foo if it doesn't have a default constructor in serialisation. the base default constructor will not help me out. — Mare Infinitus, Jun 20 '12 at 19:08
@MareInfinitus - ah - I didn't get that from your question. "Default constructor" is a bit ambiguous. — 3Dave, Jun 20 '12 at 19:11

score 7 · Accepted Answer · answered Jun 20 '12 at 18:52

7

You can't do that in an interface or attribute.

Two thoughts:

integration test: use reflection to find all relevant classes, and check them in a test
expose your serialization code in a generic API that uses the T : new() clause, i.e.
```
void Serialize<T>(T obj, ...) where T : IVeryQuickSerializable, new()
```

answered Jun 20 '12 at 18:52

Marc Gravell

1,026,079
266
2,566
2,900

Writing a wrapper is a partial solution, but maybe the fastest. Thank you. – Mare Infinitus Jun 20 '12 at 18:58
+1 for integration tests, I made a similar use of them at several times. Last time was a few days ago, to ensure that a given set of classes was decorated with a consistent combination of custom attributes. – s.m. Jun 20 '12 at 18:59
Yes, the more I read on those tests, the more I like the idea. We already have a somewhat big set of tests, but this one is missing. – Mare Infinitus Jun 20 '12 at 19:01
The constraints will get me out of this i believe. Should be only minor changes to existing code. Thank you so much! – Mare Infinitus Jun 20 '12 at 19:15

score 0 · Answer 2 · answered Jun 20 '12 at 18:54

0

There most probably are better solutions, but you could write an application that uses reflection to inspect the assembly during the post-build event.

answered Jun 20 '12 at 18:54

C.Evenhuis

25,996
2
58
72

Force implementation of default constructor

2 Answers2