Tuples printing

[bearophile via Digitalmars-d]

This is a topic I've already discussed a little in past.

In D I use tuples often, and I print them all the time, mostly 
while I write the code. Ranges of tuples are generated by some 
Phobos functions, and are generated by my map functios too. But 
if you print those ranges you quickly find a problem. A simple 
example program:


void main() {
     import std.stdio, std.typecons;

     alias RGB = Tuple!(ubyte,"R", ubyte,"G", ubyte,"B");
     const arr = [RGB(1, 2, 3), RGB(4, 5, 6), RGB(7, 8, 9)];

     writeln(arr);
}


It prints:

[const(Tuple!(ubyte, "R", ubyte, "G", ubyte, "B"))(1, 2, 3), 
const(Tuple!(ubyte, "R", ubyte, "G", ubyte, "B"))(4, 5, 6), 
const(Tuple!(ubyte, "R", ubyte, "G", ubyte, "B"))(7, 8, 9)]


If your range of tuples grows larger, the printing becomes too 
much long and too much noisy. The signal gets almost lots.

A simple solution is to print tuples inside ranges as just 
(field1, field2, ...), and keep the same printing style if you 
print a single tuple:

writeln(RGB(1, 2, 3))
writeln(arr);
==>
Tuple!(ubyte, "R", ubyte, "G", ubyte, "B"))(1, 2, 3)
[(1, 2, 3), (4, 5, 6), (7, 8, 9)]

-----------------------

There are sufficiently common situations where you want a more 
precise textual representation of a tuple (and you can't override 
the Tuple.toString). See:
https://issues.dlang.org/show_bug.cgi?id=12106

The idea comes from the syntax to format the key and values of an 
associative array, that is currently available:

import std.stdio: writefln;
void main() {
     auto aa = [1: 10, 2: 20, 3: 30];
     writefln("%(%d: %d\n%)", aa);
}


Its output:

1: 10
2: 20
3: 30


So I've suggested a similar syntax for a range of tuples:


import std.stdio: writefln;
import std.range: zip;
void main() {
     auto r1 = zip([1, 2, 3], [10, 20, 30]);
     writefln("%(%d: %d\n%)", r1);
     auto r2 = zip([1, 2, 3], [10, 20, 30], [100, 200, 300]);
     writefln("%(%d: %d, %d\n%)", r2);
}



If you use only one formatting % then it formats the whole tuple, 
otherwise it requires exactly as many % as the fields of the 
tuple. But this syntax is ambiguous when you have a range of 
1-tuples:


import std.stdio: writefln;
import std.range: zip;
void main() {
     auto r0 = zip([10, 20, 30]);
     writefln("%(%s\n%)", r0);
}


Currently this works and outputs:

Tuple!int(10)
Tuple!int(20)
Tuple!int(30)

Do you have suggestions?

Thank you, bye,
bearophile