Yes, of course. Thanks 
The fact that Vector{A{Int}} is not <: Vector{A} is what is meant by invariance, so that’s why I suggested that you probably need to read over that section again. (As explained in that section, Julia’s invariant semantics are critical for performance because it allows Vector{A{Int}} to be a “flat” array consecutive A{Int} objects in memory, rather than array of pointers to “boxes” that can hold an arbitrary A.)
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