• bearophile (70/70) Feb 25 2013 Two notes born from a Rosettacode entry

"bearophile" <bearophileHUGS lycos.com> writes:

Two notes born from a Rosettacode entry 
(http://rosettacode.org/wiki/Align_columns#D ), but general to 
deserve their own post.

This program has a bug:


import std.stdio, std.string, std.algorithm, std.range;

void main() {
     auto data =
"Given$a$txt$file$of$many$lines,$where$fields$within$a$line$
are$delineated$by$a$single$'dollar'$character,$write$a$program
that$aligns$each$column$of$fields$by$ensuring$that$words$in$each$
column$are$separated$by$at$least$one$space.
Further,$allow$for$each$word$in$a$column$to$be$either$left$
justified,$right$justified,$or$center$justified$within$its$column."
     .splitLines.map!q{ a.chomp("$").split("$") };

     int[int] maxWidths;
     foreach (line; data)
         foreach (i, word; line)
             maxWidths[i] = max(maxWidths.get(i, 0), word.length);

     foreach (just; [&leftJustify!string, &center!string,
                     &rightJustify!string])
         foreach (line; data)
             writefln("%-(%s %)", iota(line.length)
                      .map!(i => just(word, maxWidths[i], ' ')));
}



DMD gives just the error message:

test1.d(21): Error: no property 'map' for type 'Result'


Can you spot the problem?

Lately I have started to omit the () in UCFS (according to this: 
http://article.gmane.org/gmane.comp.lang.d.phobos/7222 ) and I am 
seeing several similar situations with insufficient error 
messages.

Is it possible for DMD to improve its error messages in similar 
situations?

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

This program is derived from another buggy version of same code:


import std.stdio, std.algorithm, std.typetuple, std.range;

void main() {
     auto items = [[10, 20], [30]];

     foreach (_; 0 .. 2) {
         foreach (sub; items) {
             iota(sub.length)
             .map!((i){ writeln(sub); return 0; })
             .array();
         }
     }

     writeln();

     foreach (_; TypeTuple!(0, 1)) {
         foreach (sub; items) {
             iota(sub.length)
             .map!((i){ writeln(sub); return 0; })
             .array();
         }
     }
}


Its output:

[10, 20]
[10, 20]
[30]
[10, 20]
[10, 20]
[30]

[10, 20]
[10, 20]
[30]
[30]
[30]
[30]


Can you guess why the output of the two foreach(_) is different?

Bye,
bearophile