UFCS for arguments other than first?

[Temtaime via Digitalmars-d]

On Friday, 11 November 2016 at 16:39:26 UTC, Heisenberg wrote:
> What would it take to implement the Uniform Function Call 
> Syntax for a function's argument which is not the first?
>
> Right now it is possible to do the following:
>
>> int someNumber(int a, int b)
>> {
>>     return a + b;
>> }
>>
>> void main()
>> {
>>     int n1 = 5;
>>     int n2 = n1.someNumber(n1 + 1); // Here the `n1` is `a`
>> }
>
> But it's not possible to use the `n1' as `b`, for UFCS only 
> substitutes the expression before the `.` for the first 
> argument. This limits a little bit the flexibility of UFCS. 
> What would it take to specify the argument in which UFCS is 
> going to put the expression before the `.`? This would make it 
> even more useful.
>
> For instance:
>
>> string someStr = "Yohoho!";
>> // To format and print it, one could use `printf':
>> writefln("The string is \"%s\".", someStr);
>> // But since it is not in the first place,
>> // it is not possible to use UFCS for it:
>> someStr.writefln("The string is \"%s\"."); // ^ Prints 
>> `Yohoho!'
>> // One could use tuples to pass
>> // the expanded list of strings:
>> tuple("The string is \"%s\".", someStr)[].writefln();
>> // But it would be much easier if there was
>> // some way to tell the compiler
>> // to position the argument,
>> // for example:
>> someStr&1.writefln("The string is \"%s\".");
>> //     ^            ^ argument at the position [0]
>> //     ^ argument to be put at the position [1]
>> // This could even allow to insert the argument
>> // at more than one position at once:
>> someStr&1&3&4.writefln("Say it, lass!\n" ~
>>                        "%s\nI'm a pirate!\n" ~  // someStr 
>> goes here (1)
>>                        "%s\nHe's a pirate!\n" ~ // not here (2)
>>                        "She's a pirate!\n%s" ~  // here (3)
>>                        "Ale! Rum! %s\n" ~       // and here (4)
>>                        "Wait.. Why is the rum gone?",
>>                        "You are a pirate!");    // gets shifted
>>                                                 // to position 
>> (2)

You are wrong. We can use n1 for the second parameter.

int someNumber(int a, int b)
  {
      return a + b;
  }

int main()
{
      int n1 = 5;
      return (n1.someNumber = n1); // 10
  }