Immutable native structures

[tomprimozic]

Some fields of internal structures (such as types) should be immutable. Currently, one can do this:

julia> a = complex(1,2)
1 + 2im

julia> typeof(a).names = (:re, :im, :x)
(re,im,x)

Then, a.x returns a random value, and after a call to gc() it crashes the REPL.

The getfield function should prevent this, I think. On the other hand, the types field cannot be mutated.

[pao]

#13

[JeffBezanson]

Yes, this will be fixed when we address immutability. In the mean time, just don't do it :)