Initialization of struct containing anonymous union

[Steven Schveighoffer via Digitalmars-d-learn]

On 8/14/17 10:57 AM, Carl Sturtivant wrote:
> On Monday, 14 August 2017 at 14:49:57 UTC, Steven Schveighoffer wrote:
>> On 8/14/17 10:36 AM, Carl Sturtivant wrote:
>>> On Monday, 14 August 2017 at 14:24:40 UTC, Steven Schveighoffer wrote:
>>>>
>>>> I think what the docs mean is that as soon as an anonymous union is 
>>>> present, you can't initialize anything further than the first union 
>>>> field.
>>>
>>> I understood that, hence my remark that "this is not helpful".
>>
>> OK. I thought you meant that the documentation is not helpful enough 
>> to understand what it means.
>>
>>>
>>>>> So it seems I am forced to assign explicitly to each member of the 
>>>>> struct, an ugly process.
>>>>>
>>>>> What is a nice way to solve this problem?
>>>>
>>>> I think the only way to solve it is with a constructor:
>>>>
>>>> this(int ival, double xval) { i = ival; x = xval; }
>>>
>>> As I though I made clear, I don't want write assignments to each 
>>> variable in a 50 or 100 member struct from a library when D could 
>>> supply a better solution.
>>
>> Sorry, I thought you meant to assign the fields manually outside an 
>> initializer function.
>>
>>> I can print out such a struct using writeln, but can find no way to 
>>> use that text cleaned up in source code to create such a struct. Is D 
>>> completely deficient here?
>>
>> Hm... have you tried named field initializers?
>>
>> mess m = { i: 99, x: 3.14};
>>
> 
> I could do that, but again it would involve finding the 50 or 100 names 
> and writing text that looks quite like the text of an assignment except 
> using colon instead of equals. So just as long and ugly.

Well, you only have to initialize the ones that aren't defaulted. So in 
some use cases, this is hugely beneficial.

But it seems in your case, you want to intialize everything explicitly 
(but only one member from each union).

Tried this, also works. Looks like you just have to name items after the 
unions (i.e. when you are skipping members). Ugly, but passable:

struct mess
{
     union
     {
         int i;
         string s;
     }
     double x;
     int z;
}

mess s = {99, x: 3.14, 5};

-Steve