CODEWITHSUNDEEP
c#.netgenericssyntax
Tomáš Zato
Tomáš Zato

Reputation: 53257

Generic type constraint syntax conflicts with inheritance syntax

I want to constraint a template type to specific subclass, which is done like this:

// This class contains generic list template
// but specific implementation can be used
class MyClass<T> where T: IEnumerable {}

But I also want to implement a class, without template, that's:

class MyClass: MyClassBase {}

But how do I combine those two things? This is an error:

class MyClass<T> where T: IEnumerable : MyClassBase {}

Also error:

class MyClass<T> where T: IEnumerable, : MyClassBase {}

Error:

class MyClass<T> (where T: IEnumerable) : MyClassBase {}

Error:

class MyClass<T where T: IEnumerable>: MyClassBase {}

What's the correct syntax? MSDN doesn't bother explaining it.

Upvotes: 0

Views: 260

Answers (2)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726899

The correct syntax is to specify inheritance first, and then add where:

class MyClass<T> : MyClassBase where T: IEnumerable {
}

Here is the corresponding C# grammar specifying that class_base comes ahead of type_parameter_constraints_clauses:

class_declaration ::= attributes? class_modifiers? partial? class
    identifier type_parameter_list?
    class_base?
    type_parameter_constraints_clauses? class_body ;?

Upvotes: 4

Hesam Faridmehr
Hesam Faridmehr

Reputation: 1196

private class BaseClass    { }

private class MyClass<T> : BaseClass
     where T : IEnumerable
{

}

Upvotes: 0

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