On Thursday, 5 May 2016 at 16:12:40 UTC, Steven Schveighoffer
wrote:
On 5/5/16 12:10 AM, Erik Smith wrote:
I want to have a struct template auto instantiate when the
template
parameters are defaulted or missing. Example:
struct Resource(T=int) {
static auto create() {return Resource(null);}
this(string s) {}
}
auto resource = Resource.create;
As a plain struct it works, but not as a template:
struct Resource { // works
struct Resource() { // fails
struct Resource(T=int) { // fails
At the call site, this works, but I'm hoping for a few less
symbols:
auto resource = Resource!().create;
Any ideas?
Instead of static method, use an external factory method:
static auto createResource(T = int)()
{
return Resource!T(null);
}
And I wouldn't bother with making Resource's T have a default,
as you'd still have to instantiate it with Resource!() to get
the default.
-Steve
Alias works at the cost of adding a 2nd type name:
alias Res = Resource!();
auto res = Res.create
The other problem is that the alias definition by itself
instantiates, which I can't afford.
I have createResource() now, it just doesn't fit well with the
rest of the calling styles.
There is also this approach, which might be slightly more
idiomatic
struct Resource(T) {}
struct Policy {}
auto create(alias T)() {
T!Policy r;
return r;
}
auto r = create!Resource;
