Comparing an imaginary number like an ifloat with a real one like a float:
1. Has results that differ at compile time and runtime.
2. At runtime is done in the wrong order.
3. Doesn't seem to be very meaningful, given that you can't compare complex numbers.

With respect to each issue above, here are some more details.

1. Different results at runtime and compile time.
At compile time, if the left is imaginary, then we take the imaginary part of the right side and compare the two. If the left side is real, then we take the real part of the right side and compare.
All of this is as seen in constfold.c.
At runtime, we turn both sides into complex numbers by making a missing part zero. Then, we compare the imaginary parts, and if they're equal, compare the real parts.

2. Wrong order at runtime.
In the runtime comparison described in #1 what's actually compared is right to left instead of left to right. If my program has "a < b", then "b < a" is checked.

3. Meaning?
Comparisons where at least one side is a complex number are not allowed in D. As such, is it meaningful to allow the comparisons described here, given that such numbers are treated as complex numbers and compared?

Note, all of this is strictly where one side of a compare expression is an imaginary number and the other is a real number.


Here's a sample program:

import std.stdio;

void main()
{
		cfloat	cf1 = 1 + 2i;
		cfloat	cf2 = 3 + 4i;

		ifloat	if2 = 1i;
		float	f2 = 3;
		ifloat	if3 = 4i;
		float	f3 = 2;
		ifloat  if4 = 5i;
		float   f4 = 5;

		writeln( "--- < ---" );
		writeln( if2 < f2 );
		writeln( f2 < if2 );
		writeln( if3 < f3 );
		writeln( f3 < if3 );
		writeln( if4 < f4 );
		writeln( f4 < if4 );
		writeln( 1i < 3 );
		writeln( 3 < 1i );
		writeln( 4i < 2 );
		writeln( 2 < 4i );
		writeln( 5i < 5 );
		writeln( 5 < 5i );

		writeln( "--- == ---" );
		writeln( if2 == f2 );
		writeln( f2 == if2 );
		writeln( if3 == f3 );
		writeln( f3 == if3 );
		writeln( if4 == f4 );
		writeln( f4 == if4 );
		writeln( 1i == 3 );
		writeln( 3 == 1i );
		writeln( 4i == 2 );
		writeln( 2 == 4i );
		writeln( 5i == 5 );
		writeln( 5 == 5i );

		writeln( "--- > ---" );
		writeln( if2 > f2 );
		writeln( f2 > if2 );
		writeln( if3 > f3 );
		writeln( f3 > if3 );
		writeln( if4 > f4 );
		writeln( f4 > if4 );
		writeln( 1i > 3 );
		writeln( 3 > 1i );
		writeln( 4i > 2 );
		writeln( 2 > 4i );
		writeln( 5i > 5 );
		writeln( 5 > 5i );
}