http://d.puremagic.com/issues/show_bug.cgi?id=10881

           Summary: Support %f formatting for a std.complex.complex
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: bearophile_hugs@eml.cc


--- Comment #0 from bearophile_hugs@eml.cc 2013-08-24 09:22:18 PDT ---
In dmd 2.064alpha you have to use %s to print a std.complex.complex:


import std.stdio: writefln;
import std.complex: complex;
void main() {
    auto c = complex(1.2, 3.4);
    writefln("%s", c);
    auto gaussianInteger = complex!int(1, 2);
    writefln("%s", gaussianInteger);
}


But today we can have something better so I suggest to modify the toString of those complex structs to support a basic floating point formatting too (here 3.2f is used for both parts of the complex number):

auto c = complex(1.2, 3.4);
writefln("%3.2f", c);

If you are using the uncommon Gaussian integers then probably you have to use %d:

auto gaussianInteger = complex!int(1, 2);
writefln("%10d", gaussianInteger);

If you want to format differently the two parts of a complex number, then a syntax similar to array formatting could be supported, but this is less important because I think it's a less common need, and could be left for a successive enhancement:

writefln("%(%1.2f, -1.2f%)", c);

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--- Comment #1 from hsteoh@quickfur.ath.cx 2013-08-24 16:19:16 PDT ---
Do we actually support complex!int today? From looking at the code, it seems to only support floating-point types.

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--- Comment #2 from hsteoh@quickfur.ath.cx 2013-08-24 16:21:56 PDT ---
Heh. Seem auto-promotion hid the fact that gaussian integers aren't actually supported:

import std.complex;
void main() {
        auto x = complex!int(1,2);
        pragma(msg, typeof(x)); // prints Complex!double
}

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--- Comment #3 from bearophile_hugs@eml.cc 2013-08-24 17:25:32 PDT ---
(In reply to comment #1)
> Do we actually support complex!int today? From looking at the code, it seems to only support floating-point types.

I see. I will open another issue on this. I see two possibilities: support gaussian integers too, or statically refuse code like "complex!int(1, 2)".

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--- Comment #4 from bearophile_hugs@eml.cc 2013-08-24 17:43:56 PDT ---
(In reply to comment #3)

> I see. I will open another issue on this. I see two possibilities: support gaussian integers too, or statically refuse code like "complex!int(1, 2)".

"Complex!int(1, 2)" is refused. The "complex!int(1, 2)" is not refused, but
perhaps there is not simple way to forbid that.

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--- Comment #5 from hsteoh@quickfur.ath.cx 2013-08-24 17:54:23 PDT ---
Another related issue is how field widths should be handled by the formatting functions.

Currently, toString supports a custom print format (it doesn't integrate properly with the present std.format, but don't worry about that -- I have the fix for that already). But it produces unexpected results: complex(1.2, 3.4).toString(null, "%5.2f") produces " 1.00+ 2.00i", because the format spec is just propagated to the real/imaginary parts of the number. This is unexpected because from the user's POV, the field width specifies the width for the entire complex number, not the individual parts. I'd expect the format "%5.2f" should mean field width of *entire* complex number is 5, with 2 digits precision after the decimal point. So the output should be "1.00+2.00i" because the resulting string exceeds the specified field width.

If the format was "%5.0f", I'd expect the output to be " 1+2i" (1 space padding to fill up to field width of 5), but the current result is "    1+    2i".

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--- Comment #6 from bearophile_hugs@eml.cc 2013-08-24 19:44:30 PDT ---
(In reply to comment #5)

> because the format spec
> is just propagated to the real/imaginary parts of the number. This is
> unexpected because from the user's POV, the field width specifies the width for
> the entire complex number, not the individual parts.

In my request I wrote:

> (here 3.2f is used for both parts of the complex number):

I meant that each single floating point value is formatted independently with 3.2f. This means my POV was different from the one you have assumed.

I don't know what's the best solution for this, but I think my request is simpler, just format the two values separately, this means calling and re-using the usual floating point formatting logic two times.

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--- Comment #7 from bearophile_hugs@eml.cc 2013-08-24 19:50:05 PDT ---
This is a small use case:


void main() {
    import std.stdio, std.complex, std.math;
    alias C = complex;
    immutable x = 2 ^^ 0.5 / 2;
    immutable M = [[C(x,    0.0), C(x,   0.0), C(0.0, 0.0)],
                   [C(0.0, -x),   C(0.0, x),   C(0.0, 0.0)],
                   [C(0.0,  0.0), C(0.0, 0.0), C(0.0, 1.0)]];
    writefln("[%([%(%s, %)],\n %)]]", M);
}



It prints:

[[0.707107+0i, 0.707107+0i, 0+0i],
 [0-0.707107i, 0+0.707107i, 0+0i],
 [0+0i, 0+0i, 0+1i]]

But I'd like the columns to be aligned vertically, to increase the readability of the matrix.

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--- Comment #8 from hsteoh@quickfur.ath.cx 2013-08-24 22:55:56 PDT ---
Hmm. OK, in that case, the current behaviour of the code already does what you want. :) All that's needed is to support %f directly in writefln.

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hsteoh@quickfur.ath.cx changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull


--- Comment #9 from hsteoh@quickfur.ath.cx 2013-08-24 23:12:17 PDT ---
https://github.com/D-Programming-Language/phobos/pull/1516

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