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Re: JLS 3/e -- Lots Of Errors

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  Re: JLS 3/e -- Lots Of Errors Lawrence D'Oliveiro <ldo@geek-central.gen.new_zealand> - 2011-02-05 11:33 +1300

#26129 — Re: JLS 3/e -- Lots Of Errors

Here’s an example of what I mean, from section 5.1.10, pages 89-90:

     5.1.10 Capture Conversion
     Let G name a generic type declaration with n formal type parameters A1
     ... An with corresponding bounds U1 ... Un. There exists a capture
     conversion from G<T1 ... Tn> to G<S1 ... Sn>, where, for 1 ≤ i ≤ n :
    • If Ti is a wildcard type argument (§4.5.1) of the form ? then Si is a
      fresh type variable whose upper bound is Ui[A1 := S1, ..., An := Sn]
      and whose lower bound is the null type.
    • If Ti is a wildcard type argument of the form ? extends Bi, then Si is
      a fresh type variable whose upper bound is glb(Bi, Ui[A1 := S1, ...,
      An := Sn]) and whose lower bound is the null type, where glb(V1,...
      ,Vm) is V1 & ... & Vm. It is a compile-time error if for any two
      classes (not interfaces) Vi and Vj,Vi is not a subclass of Vj or vice
      versa.
    • If Ti is a wildcard type argument of the form ? super Bi, then Si is a
      fresh type variable whose upper bound is Ui[A1 := S1, ..., An := Sn]
      and whose lower bound is Bi.

In all those three cases, Si occurs in its own definition. How are you 
supposed to make any sense of that circularity? It’s complete nonsense. The 
only way I can understand it is if all those instances of “Ui[A1 := S1, ..., 
An := Sn]” should actually be “Ui[A1 := T1, ..., An := Tn]”.

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