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

[d-bugmail at puremagic.com]

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



--- Comment #8 from Maxim Fomin <maxim at maxim-fomin.ru> 2013-10-09 23:19:45 PDT ---
(In reply to comment #6)
> (In reply to comment #5)
> > Claim is follows: this is a D valid code.
> 
> OK.
> 
> > Backing:
> > 1) AGG(1) is a struct literal (struct spec page). Note, that struct literal
> > really means struct literal, not "default struct constructor" or "implicit
> > function call" or "call expression" or any other 'creative' understaning of
> > language rules.
> > 2) Struct literal contains member initializers which should match in order and
> > type to struct member initializer (struct spec page + TDPL).
> > 3) Integer literal is valid initializer for static array of ints (TDPL).
> 
> How do you define "is a valid initializer"? The struct page
> (http://dlang.org/struct.html ?) doesn't actually define it (nor does it define
> much on what is or isn't a valid construction type.

TDPL has explicit example in the beginning of fixed array chapter.

> In my original case, S can be initialized by int, so isn't int a valid
> initializer for S? If not, why not? Just because? This is what is throwing me
> off.

struct S{int i;this(int){}}

struct AGG(T)
{
    T t;
}

void main()
{
    AGG!S ts2 = AGG!S(S(2)); //Explicit. Good.
    AGG!S ts1 = AGG!S(1); //NO! ILLEGAL REQUEST FOR IMPLICIT CONSTRUCTION!
}

Second does not work because S(1) is not a struct literal but a constructor
call. AGG!S(1) initializer now would require function call S.__ctor(1) which is
not currently supported. 

> Seems the root argument is that static arrays are the *only* type that can be
> initialized form a type that is not implicitly "it", and that this special rule
> applies *only* during aggregate construction.

It seems you starting to understand the issue (but I haven't thought whether
static arrays are only types supporting this).

> I see neither of the two points explained in struct.html, nor array.html ?

It is in TDPL. Anyway this feature was working for years.

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