Re: Why D functions paramter can not implicit infer type of Variant?
On Wednesday, 13 January 2021 at 19:38:55 UTC, Paul Backus wrote: That's what Variant is--a struct that models the universal supertype (sometimes called "Top" or "Any"). Ahh right. Good point, so it already fits.
Re: Why D functions paramter can not implicit infer type of Variant?
On Wednesday, 13 January 2021 at 18:09:08 UTC, sighoya wrote: A more natural conclusion would be to infer c to the most common supertype as other inferences would unnecessarily exclude future assignments to c. But the most common supertype doesn't seem to exist, and I'm unsure if this type can be modeled at all in D? That's what Variant is--a struct that models the universal supertype (sometimes called "Top" or "Any").
Re: Why D functions paramter can not implicit infer type of Variant?
On Wednesday, 13 January 2021 at 16:17:02 UTC, Marcone wrote:
import std;
void a(int b){
}
void main()
{
Variant c = 10;
a(c); // Error
}
Need more sugar.
Two problems:
1.) Variant is library defined, compared to the language level
there isn't a default strategy to choose int32 here, it could be
also, short, long, unsigned ... not to mention all the alias this
types.
Though it may be possible to define a default strategy but part
of the problem is how to tell D to init the type parameters
appropriately.
2.) c is mutable, what is if you return c and assign other values
of other types to it?
Determining all possibilities by traversing following assignments
leads to global type inference which no one would ever want to
have especially with support of subtyping.
A more natural conclusion would be to infer c to the most common
supertype as other inferences would unnecessarily exclude future
assignments to c. But the most common supertype doesn't seem to
exist, and I'm unsure if this type can be modeled at all in D?
Re: Why D functions paramter can not implicit infer type of Variant?
On 1/13/21 8:17 AM, Marcone wrote:
> import std;
>
> void a(int b){
> }
>
> void main()
> {
>Variant c = 10;
>a(c); // Error
> }
>
> Need more sugar.
That can't work in a strongly statically typed language. The call a(c)
is decided at compile time but Variant is not an int at compile time.
It could only work if Variant were a user-defined type that had an
automatic conversion to int with 'alias this'.
Ali
Why D functions paramter can not implicit infer type of Variant?
import std;
void a(int b){
}
void main()
{
Variant c = 10;
a(c); // Error
}
Need more sugar.
