[Issue 11206] static array can be implicitly built from items, when nested in aggregate

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http://d.puremagic.com/issues/show_bug.cgi?id=11206



--- Comment #11 from Kenji Hara <k.hara.pg at gmail.com> 2013-10-10 01:15:51 PDT ---
(In reply to comment #9)
> As I have mentioned previously, there is no inconsistency because you
> implicitly assuming that struct literal/constructors can be recursive or
> 'nested' in some sense. If you mean allowing AGG!S ts1 = AGG!S(1); in original
> example, then this is a minor enhancement.

I knot that it is an enhancement (eg. bug 7255), but I think it's necessary to
increase consistency between static array and user-defined struct type, and
it's important for more expressiveness on initializing.

The start of my thought ----
Currently, BigInt accepts built-in integers as the "valid initializer".

  BigInt num = 1;

This is expressive syntax. But, when you declare a multi-dimensional array of
BigInt, it would become too verbose.

  BigInt[128] sa = [
      BigInt(1), BigInt(2), BigInt(3), BigInt(4),
      BigInt(5), BigInt(6), BigInt(7), BigInt(8),
      ...
  ];

If T t = v; is allowed, array initializer should also allow T[n] tsa = [v1, v2,
...]; After the enhancement implemented, we will be able to write the BigInt
array declaration as:

  BigInt[128] sa = [1, 2, 3, 4, 5, 6, 7, 8, ..., 128];

---- The end of my thought

I think we could apply the same rule to the relation of struct literal syntax
arguments and corresponding struct field type.

  Agg!S agg = Agg!S(1);  // #1
  S[1] ssa = [1];    // #2

- In #1, the struct field Agg!S.val is initialized by the corresponding value 1
which is in the struct literal argument list.
- In #2, the array element ssa[1] is initialized by the corresponding value 1
which is in the array initializer argument list.

In both case, if the initialized storage typed S accepts the corresponding
value 1 *as the valid initializer*, the composite array/struct initializing
should also work.

Additional note: The following code already works currently.

  Agg!S aggr2 = {val:1};   // struct initializer syntax

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