Template constraint: T is a value type

[Gareth Foster via Digitalmars-d-learn]

Hi there,

I'm looking to write a function template that operates only on 
value types. Basically I'm looking for an equivalent of

   where T: struct

from C# (http://msdn.microsoft.com/en-us/library/d5x73970.aspx)

I was thinking that maybe using

   template Foo(T) if (is(T : struct) or is(T: union)) { ... }

or perhaps

   template Foo(T) if (!is(T : class)) { ... }

would be correct, but I fear the first may be too limiting (would 
simple data types such as int, char etc be allowed here? I'd 
guess not.) and the second may be too lax.

Any advice? Am I even going in remotely the right direction? 
Thanks.