Gotype-error: struct does not implement the interface

No, it does not implement myY, as the error clearly states:

realX does not implement myX (wrong type for Do method)
     haveDo() realY
     want Do() myY
 

The method signature must exactly match the type that implements the interface. Method signatures do not match – the return type is different. If the realY tool does not matter myY; The signature is different.

1> Adrian..:

No, it does not implement myY, because the error clearly states:

realX does not implement myX (wrong type for Do method)
     haveDo() realY
     want Do() myY
 

The method signature must exactly match the type that implements the interface. Method signatures do not match – the return type is different. If the realY tool does not matter myY; The signature is different.