Parametric types - type definition in struct name or struct argument?

[DNF]

@sadish-d

And then I can define a constructor that takes a type as a parameter if that’s what I want.

Exactly. And then you can decide whether to define a constructor for Ball(Red) or Ball(Red()).

@sadish-d

• Your first constructor takes a type, a subtype of Color, as an argument. That’s what I presume the(::type) syntax does.
• Your second constructor takes an instance of some Color, takes its type T, and creates an instance of Ball{T}.

Yes to both.

@sadish-d

The where statement is necessary if we want to use the T on the right hand side of the function definition (I think I read this somewhere).

Yes, you use this syntax in order to capture the type in a variable, T. But you could also in stead do

Ball(c::Color) = Ball{typeof(c)}()

and then Ball(Red()).