Re: [vim9script] On extending interfaces

> Also, if a concrete class has to implement both i1 and i2 explicitly,
> then i2 might as well not subclass i1.

Right, that's the approach I am currently adopting, which is fine
because my interfaces are small.

I may add that the problem with an orthogonal approach such as this:

interface I1
def Foo()
endinterface

interface I2
def Bar()
endinterface

class C implements I1, I2
...
endclass

class D implements I1, I2
...
endclass

is that there is no type for "C or D" or, more generally, for something
that "implements both I1 and I2", e.g.:

def F(X: ???)
X.Foo()
X.Bar()
enddef

where ??? = "anything implementing both I1 and I2". So, my current best
approximation is:

interface I1
def Foo()
endinterface

interface I2 # (Virtually) extends I1
def Foo()
def Bar()
endinterface

class C implements I1, I2
...
endclass

class D implements I1, I2
...
endclass

def F(X: I2)
X.Foo()
X.Bar()

def G(Y: I1)
Y.Foo()

which is perfectly fine (both F() and G() will accept objects of class
C or D), although the repetition in I2 may become a tad inconvenient if
I1 is large. Hence, my proposal.

Life.

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