Why are interfaces so restrictive?

[BCS]

In article <dvi36k$o4o$1 at digitaldaemon.com>, Jarrett Billingsley says...
>
>"BCS" <BCS_member at pathlink.com> wrote in message 
>> The difference is much like the difference between a delegate made from a 
>> class
>> method call and one from a nested function call.
>>
>> Yes, they look a lot alike, but one is a little bit more expensive.
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>"Nittering" and "nats" come to mind ;)
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>I would imagine that in any case, the compiler would optimize the access to 
>the stack frame, by dereferencing it once and keeping it in a register. 
>Seems more like a QOI issue to me.  And kind of a rare, niche issue at that. 
>I mean, how often do you need to do this? 
>
>
Interface literals? Haven’t needed them yet, however I could have used an
interface implemented with a struct yesterday.