resource structs and default constuction

[Jonathan M Davis via Digitalmars-d]

On Monday, 1 June 2015 at 16:00:20 UTC, Erik Smith wrote:
> I have a struct that uses RefCounted internally to manage a 
> database environment.    It’s basically in the same boat as 
> RefCounted itself in that it requires runtime construction.  
> Two things set it apart:
>
> 1) No-arg construction is required
> 2) The potential prevalence of this type in application code 
> and getting default initialized by mistake.
>
> This issue has been discussed before (see link below).  It 
> would be nice if this could be addressed in the language at 
> some point, but as far as I can tell, the best option I have 
> now is to put version(assert) checks in all of my member 
> functions to check for proper construction.
>
> For the default construction issue, a factory function was 
> suggested as an option.  I came up with the following approach:
>
> struct Database {
>
>      static Database create() {
>           return Database("");
>      }
>
>      static Database create(A...)(auto ref A args) {
>           return Database(args);
>      }
>
>      this(string uri) {…}
>      this(Config config) {…}
>      ...
> }
>
> The first static function provides a way to default construct.  
> The 2nd static function provide uniformity with all of the 
> other constructors that might be present.
>
> Might this be a good idiom to apply for resource managing 
> structs in general?
>
> erik
>
>
> previous forum discussion on default constructors:
> http://forum.dlang.org/thread/fgldbozuneoldxjrwxje@forum.dlang.org?page=5

If you want to force that a constructor be called rather than 
using the init value, then you need to make the init value 
unusable by @disabling this(). Then the caller _has_ to 
explicitly call a constructor or factory function. Regardless, if 
you want a constructor that takes no arguments for a struct, you 
need a factory function, since you can't have struct constructors 
with no parameters.

- Jonathan M Davis