How to instantiate a map with multiple functions

[Jay Norwood via Digitalmars-d-learn]

I'm playing around with something also trying to apply multiple 
functions.
In my case, a sample is some related group of measurements taken 
simultaneously, and I'm calculating a group of metrics from the 
measured data of each sample.

This produces the correct results for the input data, and it 
seems pretty clear what functions are being applied.

I would probably want to associate names with the tuple metric 
results, and I've seen that somewhere in the docs in parameter 
tuples.   I suppose I'll try those in place of the current tuple 
...

import std.stdio;
import std.algorithm;
import std.conv;
import std.range;
import std.typecons;

struct S { ulong a; ulong b; ulong c; ulong d; double e; ulong f;}

ulong f1(ref S s) { with(s){return a+b;}}
double f2(ref S s) { with(s){return (c+d)/e;}}
double f3(ref S s) { with(s){return (c+f)/e;}}

int main()
{

	S[10] samples;
	// initialize some values
	foreach ( int i, ref s; samples){
		int j=i+1;
		with (s){
			a=j; b=j*2; c=j*3; d=j*4; e=j*10; f=j*5;
		}
	}

	// apply several functions on each  sample
	samples.each!((int i, ref 
a)=>tuple(i,f1(a),f2(a),f3(a)).writeln());
	return 0;
}

========== output is

Tuple!(int, ulong, double, double)(0, 3, 0.7, 0.8)
Tuple!(int, ulong, double, double)(1, 6, 0.7, 0.8)
Tuple!(int, ulong, double, double)(2, 9, 0.7, 0.8)
Tuple!(int, ulong, double, double)(3, 12, 0.7, 0.8)
Tuple!(int, ulong, double, double)(4, 15, 0.7, 0.8)
Tuple!(int, ulong, double, double)(5, 18, 0.7, 0.8)
Tuple!(int, ulong, double, double)(6, 21, 0.7, 0.8)
Tuple!(int, ulong, double, double)(7, 24, 0.7, 0.8)
Tuple!(int, ulong, double, double)(8, 27, 0.7, 0.8)
Tuple!(int, ulong, double, double)(9, 30, 0.7, 0.8)