• sai (10/10) Jul 27 2020 I remember the reason D has built in complex numbers is because
• Guillaume Piolat (10/16) Jul 28 2020 I guess it's not considered a worthy use of D compiler engineers
• Seb (29/37) Jul 28 2020 Hehe, my guess is that std.complex wasn't written by Walter and

sai <sai dummy.com> writes:

I remember the reason D has built in complex numbers is because 
it supposed to give correct results, as mentioned at the bottom 
here: https://digitalmars.com/d/1.0/cppcomplex.html

And the math checks out: https://run.dlang.io/is/b5eyuD

So I am curious why the complex class in the library was 
introduced and the builtin complex numbers are deprecated now?

And how to avoid errors like the above when using the complex 
library?

Thanks
Sai

Guillaume Piolat <first.name gmail.com> writes:

On Tuesday, 28 July 2020 at 01:24:16 UTC, sai wrote:
 I remember the reason D has built in complex numbers is because 
 it supposed to give correct results, as mentioned at the bottom 
 here: https://digitalmars.com/d/1.0/cppcomplex.html

 And the math checks out: https://run.dlang.io/is/b5eyuD

 So I am curious why the complex class in the library was 
 introduced and the builtin complex numbers are deprecated now?

I guess it's not considered a worthy use of D compiler engineers 
time.
The decision to remove them was taken long ago.
That said, we do use complex numbers and appreciate them, it 
would take work if they were to be actually removed... and that 
will probably happen.

But it's not really an efficiency or precision concern, efficient 
code using complex sometimes use split format, and this code is 
often vectorized anyway using SIMD.

Seb <seb wilzba.ch> writes:

On Tuesday, 28 July 2020 at 01:24:16 UTC, sai wrote:
 I remember the reason D has built in complex numbers is because 
 it supposed to give correct results, as mentioned at the bottom 
 here:

Hehe, my guess is that std.complex wasn't written by Walter and 
this special case was overlooked.

See also: 
https://github.com/dlang/phobos/blob/cd2ba0d2c378a893ec0eaefc57b87d0770a1990c/std/complex.d#L345-L347

 So I am curious why the complex class in the library was 
 introduced

Supporting complex numbers requires a lot of work in the frontend.
For many features that D supports one needs to manually maintain 
special cases for complex numbers.
This has led to a lot of bugs and as complex numbers aren't very 
heavily used there are likely many which haven't surfaced yet.

A library solution provides almost the same interface and 
usability to the user. I guess the only missing thing is that 
it's a bit more verbose, but in theory the compiler could lower 
complex numbers to `std.complex` calls.

tl;dr:
- low usage of complex number to justify big complexity in 
compiler
- better maintainability as a library

The current philosophy is that everything that can be done in a 
library, should be done in a library to reduce the burden on the 
compiler.

 and the builtin complex numbers are deprecated now?

Technically they aren't deprecated yet (only discouraged to use). 
There was some work done in Phobos to support the deprecation PR 
for DMD (that's why you get the deprecation message when trying 
to print them), but the DMD deprecation PR stalled:

https://github.com/dlang/dmd/pull/7640

 And how to avoid errors like the above when using the complex 
 library?

3i (builtin) and complex(0, 3) (library) are different types.

To avoid deprecation errors, the `complex` (library) and not the 
to-be-deprecated built-in types should be used.