[sv-bc] 2380: a proposal requiring element equivalence

Last week's discussions were somewhat inconclusive
but it seems clear we should preserve the 
requirement that array elements be type-equivalent
for the arrays to be assignment compatible. 
I went through the relevant text as carefully 
as I could, and rewrote the proposal to insist 
on type equivalence; it's now attached as an 
alternative version.  PLEASE NOTE there are 
now TWO QUITE DIFFERENT proposals attached to
2380:  "v1" relaxing the rules to allow
assignment compatible elements, "v2" affirming
the need for type-equivalent elements.

Good features of the new (v2) proposal:
- No problem with back-compatibility of bitstream 
  casts; that all stays the same as 1800-2005.
- BC's wish for stricter type checking on array
  copy operations appears to be satisfied.
- The loophole provided by unpacked array 
  concatenation is still there, allowing
  copy of 1-dimensional arrays with merely
  assignment compatible element types:
    arr1 =  arr2 ; // needs type-equivalent elements
    arr1 = {arr2}; // needs assignment-compatible elements

Less good:
- Strange asymmetry between rules for the outermost
  (slowest-varying) dimension and all the others,
  especially when a mix of queue/dynamic/fixed
  dimensions is present.
- No simple way to copy multi-dimensional arrays
  with elements that are assignment compatible but 
  not equivalent.

Please review.

Thanks
-- 
Jonathan Bromley



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