First and foremost, thanks for this nice description of interfaces! If you understand that an interface value is two words wide and it contains a pointer to th

First and foremost, thanks for this nice description of interfaces! If you understand that an interface value is two words wide and it contains a pointer to the underlying data, that’s typically enough to avoid common pitfalls. Except for one: namely, if a variable v that has an interface as its type and the value pointer is nil and the type pointer isn't, then v != nil. In other words, if an interface value is internally represented as: {*Type, *Value} Then: {&DogType, nil} != nil {nil, nil} == nil This can lead to results that are initially surprising. For a description and an example: http://golang.org/doc/go_faq.html#nil_error http://golang.org/doc/go_faq.html#nil_error