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digitalmars.D.bugs - [Issue 10881] New: Support %f formatting for a std.complex.complex

reply d-bugmail puremagic.com writes:
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



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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next sibling parent d-bugmail puremagic.com writes:
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Do we actually support complex!int today? From looking at the code, it seems to
only support floating-point types.

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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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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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 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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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 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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prev sibling next sibling parent d-bugmail puremagic.com writes:
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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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prev sibling next sibling parent d-bugmail puremagic.com writes:
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 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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prev sibling next sibling parent d-bugmail puremagic.com writes:
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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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prev sibling next sibling parent d-bugmail puremagic.com writes:
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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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prev sibling next sibling parent d-bugmail puremagic.com writes:
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hsteoh quickfur.ath.cx changed:

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



https://github.com/D-Programming-Language/phobos/pull/1516

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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Commit pushed to master at https://github.com/D-Programming-Language/phobos

https://github.com/D-Programming-Language/phobos/commit/627d178f87423ba8b6059216ae1ca3fc8a2b2f29


Fix issue 10881: support writefln("%f") of complex numbers

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prev sibling next sibling parent d-bugmail puremagic.com writes:
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bearophile_hugs eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED





 Commit pushed to master at https://github.com/D-Programming-Language/phobos


Now using this formatting string, for the given matrix:
"[%([%(%1.3f, %)],\n %)]]"

It outputs:

[[0.707+0.000i, 0.707+0.000i, 0.000+0.000i],
 [0.000-0.707i, 0.000+0.707i, 0.000+0.000i],
 [0.000+0.000i, 0.000+0.000i, 0.000+1.000i]]

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prev sibling parent d-bugmail puremagic.com writes:
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monarchdodra gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |monarchdodra gmail.com







 Commit pushed to master at https://github.com/D-Programming-Language/phobos


 
 Now using this formatting string, for the given matrix:
 "[%([%(%1.3f, %)],\n %)]]"
 
 It outputs:
 
 [[0.707+0.000i, 0.707+0.000i, 0.000+0.000i],
  [0.000-0.707i, 0.000+0.707i, 0.000+0.000i],
  [0.000+0.000i, 0.000+0.000i, 0.000+1.000i]]


For anybody reading this on forum.dlang.org: please view the entry on the bug
tracker: There *is* a space that prefixes those lines, and they are all
actually perfectly aligned.

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