• Lukanian (22/22) Jun 09 Why UFCS doesn't work with "with" statement?
• Doigt (7/29) Jun 09 It took me a while what you were trying to do, but I think I get
• Quirin Schroll (9/31) Jun 27 The `with` block changes the lookup rule so that unqualified

Lukanian <nanaipenero forum.com> writes:

Why UFCS doesn't work with "with" statement?

```d
struct MyStruct1
{
   int a, b;
   int sum(){
     return a+b;
   }
}

int difference(ref MyStruct1 self)
{
   return self.a-self.b;

}

// in main()

MyStruct1 s = { 1, 2 };

s.difference().writeln; // works fine

with(s){
   sum().writeln;
   difference().writeln; // error: too few arguments, expected 1, 
got 0
}
```

Doigt <labog outlook.com> writes:

On Monday, 9 June 2025 at 11:39:15 UTC, Lukanian wrote:
 Why UFCS doesn't work with "with" statement?

 ```d
 struct MyStruct1
 {
   int a, b;
   int sum(){
     return a+b;
   }
 }

 int difference(ref MyStruct1 self)
 {
   return self.a-self.b;

 }

 // in main()

 MyStruct1 s = { 1, 2 };

 s.difference().writeln; // works fine

 with(s){
   sum().writeln;
   difference().writeln; // error: too few arguments, expected 
 1, got 0
 }
 ```

It took me a while what you were trying to do, but I think I get 
it now. I'm not an expert on D, but from what I understand, the 
reason why it doesn't work is because the difference function is 
not a method of the struct. The "with" keyword works what's a 
member of the argument. So essentially yeah, you're calling 
difference without any argument.

Quirin Schroll <qs.il.paperinik gmail.com> writes:

On Monday, 9 June 2025 at 11:39:15 UTC, Lukanian wrote:
 Why UFCS doesn't work with "with" statement?

 ```d
 struct MyStruct1
 {
   int a, b;
   int sum(){
     return a+b;
   }
 }

 int difference(ref MyStruct1 self)
 {
   return self.a-self.b;

 }

 // in main()

 MyStruct1 s = { 1, 2 };

 s.difference().writeln; // works fine

 with(s){
   sum().writeln;
   difference().writeln; // error: too few arguments, expected 
 1, got 0
 }
 ```

The `with` block changes the lookup rule so that unqualified 
symbols (`sum` and `difference` in this case) are looked up in 
the scope of the (type of) the `with` argument first, only then 
normal lookup rules (innermost scope first) apply. What `with(x)` 
doesn’t do is try to resolve any unqualified symbol `s` as `x.s`. 
If it did that, your code would work.

UFCS doesn’t make members and non-members equivalent, it’s just a 
calling syntax that works in *some* cases.