This code:


import std.stdio;
void main() {
     auto mat = [[1, 2, 3],
                 [4, 5, 6],
                 [7, 8, 9]];

     writefln("%(%(%d %)\n%)", mat);
     writeln();

     writefln("[%(%(%d %)\n%)]", mat);
     writeln();

     writefln("[%([%(%d %)]\n%)]", mat);
     writeln();
}


Prints:

1 2 3
4 5 6
7 8 9

[1 2 3
4 5 6
7 8 9]

[[1 2 3]
[4 5 6]
[7 8 9]


Do you know why the last closed square bracket is missing?

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

The following is just a note. The formatting syntax for arrays is
rather powerful, it allows you to pretty print a matrix:

import std.stdio;
void main() {
     auto mat = [[1, 2, 3],
                 [4, 15, 6],
                 [7, 8, 9]];
     writefln("[%([%(%2d, %)],\n %)]]", mat);
}


That outputs:

[[ 1,  2,  3],
  [ 4, 15,  6],
  [ 7,  8,  9]]

But all the columns must have the same width, so the first and
third column waste space. So you can't write:

[[1,  2, 3],
  [4, 15, 6],
  [7,  8, 9]]

To do it you have to pre-process the matrix, and create a matrix
of already smartly formatted strings, or better write a pretty
printing function (that belongs in Phobos. Python has it in its
'pprint' standard library module).

Bye,
bearophile

> import std.stdio;
> void main() {
>      auto mat = [[1, 2, 3],
>                  [4, 15, 6],
>                  [7, 8, 9]];
>      writefln("[%([%(%2d, %)],\n %)]]", mat);
> }
>
>
> That outputs:
>
> [[ 1,  2,  3],
>   [ 4, 15,  6],
>   [ 7,  8,  9]]

Sorry, the dlang forum online interface has added an extra leading space on only certain lines.

I use 4 spaces indents in such code.

Bye,
bearophile

On 3/21/12, bearophile <bearophileHUGS@lycos.com> wrote:
> The following is just a note. The formatting syntax for arrays is rather powerful, it allows you to pretty print a matrix.

I didn't know that! Is this documented anywhere?

Andrej Mitrovic:

> I didn't know that! Is this documented anywhere?

It's documented formally, but I see no usage examples of the nested formatting syntax:
http://dlang.org/phobos/std_format.html

Bye,
bearophile

On Wednesday, 21 March 2012 at 01:26:23 UTC, bearophile wrote:
> import std.stdio;
> void main() {
>      auto mat = [[1, 2, 3],
>                  [4, 5, 6],
>                  [7, 8, 9]];
>
>      writefln("%(%(%d %)\n%)", mat);
>      writeln();
>
>      writefln("[%(%(%d %)\n%)]", mat);
>      writeln();
>
>      writefln("[%([%(%d %)]\n%)]", mat);
>      writeln();
> }
>
> Prints:
>
> 1 2 3
> 4 5 6
> 7 8 9
>
> [1 2 3
> 4 5 6
> 7 8 9]
>
> [[1 2 3]
> [4 5 6]
> [7 8 9]
>
>
> Do you know why the last closed square bracket is missing?

You can use %| format specifier to specify element separator.

(It was proposed in https://github.com/D-Programming-Language/phobos/pull/298 .
It is not yet documented, but already merged in Phobos.)

import std.stdio;
void main() {
     auto mat = [[1, 2, 3],
                 [4, 5, 6],
                 [7, 8, 9]];

     writefln("[%([%(%d %)]%|\n%)]", mat);
     // specify "\n" as a separator
}

Prints:

[[1 2 3]
[4 5 6]
[7 8 9]]