Why is some ordering enforced in generic parameter constraints?

Question

When defining a generic type parameter\'s constraints, we have to put class() at the front and new() at the end, for example.

Why is this,

Answer 1

Like most syntax related questions, the basic answer is because the spec says so. We get the following grammar for generic type constraints from the C# 5.0 spec (Section 10.1.5)

type-parameter-constraints:

primary-constraint 
secondary-constraints
constructor-constraint 
primary-constraint   ,   secondary-constraints
primary-constraint   ,   constructor-constraint 
secondary-constraints ,   constructor-constraint 
primary-constraint   ,  secondary-constraints   ,   constructor-constraint 

primary-constraint:

class-type 
class 
struct 

secondary-constraints:

interface-type
type-parameter 
secondary-constraints   ,   interface-type
secondary-constraints   ,   type-parameter

constructor-constraint:

new (   )

Eric Lippert has done an excellent job of explaining why it was designed this way, so I won't expound on that.