Re: [PATCH v2 3/8] qnum: QNumValue type for QNum value literals

[Eduardo Habkost]

On Thu, Nov 19, 2020 at 01:21:58PM -0500, Eduardo Habkost wrote:
> On Thu, Nov 19, 2020 at 11:24:52AM +0100, Markus Armbruster wrote:
[...]
> > >> > > +    return qnum_from_value((QNumValue) QNUM_VAL_INT(value));
> > 
> > No space between between (type) and its operand, please.
> > 
> > Could we lift the cast into the macro somehow?
> 
> I think we can.  I had thought the cast in the macro would break
> usage as static variable initializers.  I was wrong.

Actually, including the cast in the macro breaks QLIT_QDICT
initializers (which use (QLitDictEntry[]) compound literals), and
I don't know why.

Compound literals in initializers of static variables is a GCC
extension.  I don't understand why it doesn't work inside array
compound literals, though.

Any language lawyers around?

This works:

  typedef struct QLit {
      int x, y;
  } QLit;
  
  typedef struct Entry {
      int key;
      QLit value;
  } Entry;
  
  Entry e = { .key = 0, .value = (QLit) { 1,   2 } };

This works:

  Entry *es1 = (Entry[]) {
      { .key = 0, .value = { 1,   2 } },
  };

But this doesn't:

  Entry *es2 = (Entry[]) {
      { .key = 0, .value = (QLit) { 1,   2 } },
  };

dict.c:16:24: error: initializer element is not constant
   16 | Entry *es2 = (Entry[]) {
      |                        ^
dict.c:16:24: note: (near initialization for ‘es2’)

(gcc (GCC) 10.2.1 20201005 (Red Hat 10.2.1-5))

-- 
Eduardo