golang interface compliance compile type check

Question

I see the following statements from camlistore(http://code.google.com/p/camlistore/source/browse/pkg/cacher/cacher.go).

var (
        _ blobref.StreamingFet         


        

Answer 1

(*T)(nil) is a Conversion. In this case it stands for a typed nil, ie. the same value which, for example

var p *T

has before assigning anything to it.

The standard syntax of a conversion is T(expr), but the priority of the * would bind it wrongly in

*T(expr)

This syntax means dereferencing the return value of function T with one argument expr. That's why the conversion has an alternative syntax:

(T)(expr)

where T can of course be *U. Therefore

(*U)(expr)

is the generalized form of what you see in the Camlistore repository.