by kaushansky:

The following doesn't compile:
  m:=make(map[interface{}] int);
  m[1]=0;

It complains that "1" is not an interface{}. However, compiler
automatically converts int to interface{} when passed as a parameter to
function expecting interface{}, and in general, it's assignment-compatible
with interface{}.
Explicit type cast (interface{})(1) works fine.
(Problem is not specific to int - any other type will fail either)