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)
I'm sure there are loads of corner cases this doesn't cover, but:
template inPos(uint n, alias f)
{
auto inPos(Args...)(auto ref Args args)
{
return f(args[1 .. n+1], args[0], args[n+1 .. $]);
}
}
import std.stdio;
alias formatSecond = inPos!(1, writefln);
void main()
{
1.writeln(2,3,4,5);
1.inPos!(2, writeln)(2,3,4,5);
42.formatSecond("The answer is %d");
}
and of course you could easily develop more powerful templates
that could do any other order manipulations you like.
