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Compiler Error CS0409

Visual Studio 2008

A constraint clause has already been specified for type parameter 'type parameter'. All of the constraints for a type parameter must be specified in a single where clause.

Multiple constraint clauses (where clauses) were found for a single type parameter. Remove the extraneous where clause, or correct the where clauses so that a unique type parameter in each clause.

// CS0409.cs
interface I
{
}

class C<T1, T2> where T1 : I where T1 : I  // CS0409 – T1 used twice
{
}
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