Multiple inheritance

[jacobwilliams]

Why not allow multiple inheritance? I believe some think this is a bad thing, but from time to time I wish we had it.

Example:

type,extends(base1,base2),public :: myclass
end type myclass

Probably it was discussed at some point?

[FortranFan]

Fyi for the readers, here are a couple of articles that might be of interest:

Why doesn’t C# support multiple inheritance?

Why not multiple inheritance? Find out why Java's creators prohibited multiple inheritance

[certik]

I feel this feature is the kind of feature that depends on having a long term plan, see #59. The long term plan will then determine whether this is on its path, or not.

As I mentioned in #59, the generic templates should allow an effective "multiple inheritance", so then this feature as proposed here would be superfluous and it'd be better not to have it, to keep the language smaller, without loosing any expressiveness. However, if we decide in #59 that we do not want templates, then this feature might be more compelling.

[klausler]

Would common base classes be duplicated or combined like C++ virtual bases?

[vansnyder]

I read a long time ago, but I don't remember where (maybe in something that Leslie Hatton wrote), that some language theorist had proven that multiple inheritance is never required. The argument against it is usually entitled "the dreaded diamond-shaped inheritance diagram."