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Why do you care if you accidentally implement an interface?

by NateDad 12y ago

dragonwriter 12y ago
Because conforming to the signatures necessary to implement an interface doesn't imply confirming to its semantics, so accidental interface "implementations" are a type-safety problem.
- NateDad 12y ago
  They're really not. You still have to have someone pass your type into something expecting an interface. It's no different than passing a string into something expecting a path when you pass it an html document... at some point the programmer needs to decide if passing the value into the method makes sense. In the canonical example: type Boat interface { Launch() } func LaunchBoat(b Boat) { // do some boat stuff b.Launch() } type NuclearMissile struct{} func (nm NuclearMissile) Launch() { // launch nuclear missile } func main() { rocket := NuclearMissile{} LaunchBoat(rocket) } Sure, this compiles, but the code doesn't make any sense. Lots of things compile, that doesn't mean the code makes sense. At some point it's the programmer's responsibility to think a little.
  - dragonwriter 12y ago
    > You still have to have someone pass your type into something expecting an interface. Yes, that's generally the case with type-safety problems, even with the type-safety problem existing, it takes an actual programming error for it to become a problem -- and that is, indeed, the standard response of people saying type-safety isn't important (usually, though, its not a reason people would say something isn't a type-safety problem.) And its not completely invalid -- there is a reason that in a world dominated by static-typed languages with limiting type systems, dynamic languages like Ruby and Python that don't offer type safety but do offer a lot of flexibility that the type systems of C++/Java/etc. made, at best, cumbersome to acheive. OTOH, if you are choosing a language with the extra ceremony involved in static typing, its kind of a big step back to not even get the level of safety with interfaces that you'd get with C#/Java, much less a more modern, expressive static type system.

Why do you care if you accidentally implement an interface?

by NateDad 12y ago

Why do you care if you accidentally implement an interface?

Because conforming to the signatures necessary to implement an interface doesn't imply confirming to its semantics, so accidental interface "implementations" are a type-safety problem.

NateDad 12y ago
They're really not. You still have to have someone pass your type into something expecting an interface. It's no different than passing a string into something expecting a path when you pass it an html document... at some point the programmer needs to decide if passing the value into the method makes sense. In the canonical example: type Boat interface { Launch() } func LaunchBoat(b Boat) { // do some boat stuff b.Launch() } type NuclearMissile struct{} func (nm NuclearMissile) Launch() { // launch nuclear missile } func main() { rocket := NuclearMissile{} LaunchBoat(rocket) } Sure, this compiles, but the code doesn't make any sense. Lots of things compile, that doesn't mean the code makes sense. At some point it's the programmer's responsibility to think a little.
- dragonwriter 12y ago
  > You still have to have someone pass your type into something expecting an interface. Yes, that's generally the case with type-safety problems, even with the type-safety problem existing, it takes an actual programming error for it to become a problem -- and that is, indeed, the standard response of people saying type-safety isn't important (usually, though, its not a reason people would say something isn't a type-safety problem.) And its not completely invalid -- there is a reason that in a world dominated by static-typed languages with limiting type systems, dynamic languages like Ruby and Python that don't offer type safety but do offer a lot of flexibility that the type systems of C++/Java/etc. made, at best, cumbersome to acheive. OTOH, if you are choosing a language with the extra ceremony involved in static typing, its kind of a big step back to not even get the level of safety with interfaces that you'd get with C#/Java, much less a more modern, expressive static type system.