www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Parameters of overloaded templated function

reply frame <frame86 live.com> writes:
So `__traits(getOverloads)` returns also templated members and 
`__traits(isTemplate)` can select those members. Unfortunately, 
`Parameters!` does not work with the templated member. How can I 
pass a symbol of T or A... to `Parameters!` as desired type 
without instantiating the template?

```d
fun(T, A...)(T arg, string foo, int bar, A args); // some overload
```

Assuming T is just an `int`, I cannot apply this type. The 
compiler is forgetting the actual overload:

```d
template getParams(alias overload) {
   static if (__traits(isTemplate, overload)) {
     alias typed = overload!int // error: fun(...) matches more 
than one template declaration
     alias getParams = Parameters!typed;
   }
}
```
May 09 2022
parent reply Tejas <notrealemail gmail.com> writes:
On Tuesday, 10 May 2022 at 01:00:24 UTC, frame wrote:

 So `__traits(getOverloads)` returns also templated members and 
 `__traits(isTemplate)` can select those members. Unfortunately, 
 `Parameters!` does not work with the templated member. How can 
 I pass a symbol of T or A... to `Parameters!` as desired type 
 without instantiating the template?

 ```d
 fun(T, A...)(T arg, string foo, int bar, A args); // some 
 overload
 ```

 Assuming T is just an `int`, I cannot apply this type. The 
 compiler is forgetting the actual overload:

 ```d
 template getParams(alias overload) {
   static if (__traits(isTemplate, overload)) {
     alias typed = overload!int // error: fun(...) matches more 
 than one template declaration
     alias getParams = Parameters!typed;
   }
 }
 ```


Can you try
```d
template getParams(alias overload) {
   static if (__traits(isTemplate, overload)) {
     //alias typed = overload!int // error: fun(...) matches more 
than one template declaration
     alias getParams = Parameters!(overload!int); //don't use 
alias, send the argument directly
   }
}
```
May 09 2022
parent reply frame <frame86 live.com> writes:
On Tuesday, 10 May 2022 at 03:18:14 UTC, Tejas wrote:

 Can you try


Makes no difference.
May 10 2022
parent reply frame <frame86 live.com> writes:
On Tuesday, 10 May 2022 at 11:26:44 UTC, frame wrote:

 On Tuesday, 10 May 2022 at 03:18:14 UTC, Tejas wrote:

 Can you try


 Makes no difference.


OK, I tried it in separate test and works. Weird, I already tried 
that before, there must be something wrong with my other template.

Thanks
May 10 2022
parent reply Tejas <notrealemail gmail.com> writes:
On Tuesday, 10 May 2022 at 11:33:24 UTC, frame wrote:

 On Tuesday, 10 May 2022 at 11:26:44 UTC, frame wrote:

 On Tuesday, 10 May 2022 at 03:18:14 UTC, Tejas wrote:

 Can you try


 Makes no difference.


 OK, I tried it in separate test and works. Weird, I already 
 tried that before, there must be something wrong with my other 
 template.

 Thanks


Using aliases as parameters doesn't work(and the DIP that wanted 
to have this behaviour was de facto rejected)

https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1023.md

But considering you're passing it as an argument, not a formal 
parameter, it should've worked... Idk what's happening there

Try
```d
alias getParams = Parameters!(typed);//add the parenthesis
```
_Maybe_ it's not taking the stuff after the second `!` when it 
substitutes the alias `typed`?
May 10 2022
next sibling parent frame <frame86 live.com> writes:
On Tuesday, 10 May 2022 at 12:12:13 UTC, Tejas wrote:


 Using aliases as parameters doesn't work(and the DIP that 
 wanted to have this behaviour was de facto rejected)

 https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1023.md

 But considering you're passing it as an argument, not a formal 
 parameter, it should've worked... Idk what's happening there


I have break it down to a `static if` after that the compiler 
gets confused:
```d
static if(__traits(isTemplate, overload)) {
   // compiler knows it is a template but error is something about 
an aliased function in further processing
}
```

However, changing it to `isSomeFunction!overload` and just 
passing the type argument otherwise, compiles. Not very clean, 
though.
May 10 2022
prev sibling parent Mike Parker <aldacron gmail.com> writes:
On Tuesday, 10 May 2022 at 12:12:13 UTC, Tejas wrote:

 Using aliases as parameters doesn't work(and the DIP that 
 wanted to have this behaviour was de facto rejected)

 https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1023.md


No, it wasn't rejected. The author decided it needed reworking 
after one round of review, but he didn't have the time for it. So 
it was marked "Postponed". He was willing to turn it over to 
someone else, if anyone is interested.
May 10 2022