implement `Add` and `Sub` for `Complex` by folkertdev · Pull Request #161227 · rust-lang/rust

folkertdev · 2026-08-17T10:52:06Z

tracking issue: #154023

Adds the Add and Sub implementations described in the tracking issue. Some notes

I also added a derive for Eq, which is useful for Complex<{integer}>
The versions that add/sub by a scalar need a Copy bound. That seems fine for most actual use cases.

Apparently num_complex will Clone in these operations https://docs.rs/num-complex/latest/num_complex/struct.Complex.html#impl-Add%3CT%3E-for-%26Complex%3CT%3E, but that seems unlike core to me. Anyhow, libs can re-litigate that later.

rustbot · 2026-08-17T10:52:12Z

r? @JohnTitor

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beetrees · 2026-08-17T13:15:27Z

+impl<T: Add<Output = T>> Add<Self> for Complex<T> {
+    type Output = Complex<T::Output>;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        Self::new(self.re + rhs.re, self.im + rhs.im)
+    }
+}


Any reason to limit the RHS and Output types to T? This could be more generic based on the Add implementation of T, e.g.:

Suggested change

impl<T: Add<Output = T>> Add<Self> for Complex<T> {

type Output = Complex<T::Output>;

fn add(self, rhs: Self) -> Self::Output {

Self::new(self.re + rhs.re, self.im + rhs.im)

}

}

impl<T: Add, U> Add<Complex> for Complex<T> {

type Output = Complex<T::Output>;

fn add(self, rhs: Complex) -> Self::Output {

Complex::new(self.re + rhs.re, self.im + rhs.im)

}

}

Similar thinking applies to the Sub<Self> implementation. The Add<T> and Sub<T> need RHS to be T to avoid overlapping trait impls, but Output doesn't need to be limited.

View changes since the review

That runs into a conflicting impl error. (it's important that Complex implements Copy for that error to show up)

https://godbolt.org/z/ExhY3oacd

That makes sense. Just removing the <Output = T> shouldn't cause any issues since it's just an associated type (compiler explorer), so doing that seems worthwhile (e.g. this would allow usage with Add/Sub impls like those in rustc_apfloat)

Sure, that seems fine. Fixed

The <Output = T> on the other two impls could also be removed?

btnlq

$(a + bi) + c = (a + bi) + (c + 0i) = (a+c) + bi$
See num-complex implementation

View changes since this review

folkertdev · 2026-08-18T09:54:55Z

Oof, it's been a while since university I guess, thanks. That removes the Copy bound, but does re-introduce the Output = T bound because the imaginary component doesn't update and is still of type T.

rustbot · 2026-08-20T21:06:58Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

folkertdev · 2026-08-25T15:31:43Z

I believe you wanted more review work

r? nia-e

scottmcm · 2026-08-27T19:01:46Z

+impl<T: Add> Add<Self> for Complex<T> {
+    type Output = Complex<T::Output>;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        Complex::new(self.re + rhs.re, self.im + rhs.im)
+    }
+}


This really seems like it should be

Suggested change

impl<T: Add> Add<Self> for Complex<T> {

type Output = Complex<T::Output>;

fn add(self, rhs: Self) -> Self::Output {

Complex::new(self.re + rhs.re, self.im + rhs.im)

}

}

impl<T: Add, U> Add<Complex> for Complex<T> {

type Output = Complex<<T as Add>::Output>;

fn add(self, rhs: Self) -> Self::Output {

Complex::new(self.re + rhs.re, self.im + rhs.im)

}

}

since I see no reason to restrict it to T: Add<T>.

View changes since the review

That does not work because it conflicts with the implementation of add with a scalar right below

#[unstable(feature = "complex_numbers", issue = "154023")] impl<T: Add<Output = T>> Add<T> for Complex<T> { type Output = Complex<T::Output>; fn add(self, rhs: T) -> Self::Output { Complex::new(self.re + rhs, self.im) } }

folkertdev · 2026-08-31T16:52:21Z

I'd quite like to build on top of this, it's all unstable surface area that can be re-litigated later, so I'd appreciate a review from someone here.

nia-e · 2026-08-31T19:47:00Z

eek, i've been a bit busy. I should be able to get to this in a day or two but if you need a faster review feel free to r? someone else

nia-e · 2026-09-03T15:18:51Z

@bors r+

rust-bors · 2026-09-03T15:18:54Z

📌 Commit d48bdef has been approved by nia-e

It is now in the queue for this repository.

implement `Add` and `Sub` for `Complex` tracking issue: rust-lang#154023 Adds the `Add` and `Sub` implementations described in the tracking issue. Some notes - I also added a derive for `Eq`, which is useful for `Complex<{integer}>` - The versions that add/sub by a scalar need a `Copy` bound. That seems fine for most actual use cases. Apparently `num_complex` will `Clone` in these operations https://docs.rs/num-complex/latest/num_complex/struct.Complex.html#impl-Add%3CT%3E-for-%26Complex%3CT%3E, but that seems unlike `core` to me. Anyhow, libs can re-litigate that later.

…uwer Rollup of 12 pull requests Successful merges: - #161227 (implement `Add` and `Sub` for `Complex`) - #161280 (make target feature ABI check a hard error on ARM) - #161893 (Add custom allocator support to `(try_)map` on `UniqueArc` and `UniqueRc`) - #162154 (fix[154166]: closure debug capture print) - #161951 (Windows: add fallback if `canonicalize` fails) - #162173 (fix supposedly unreachable `bug!` being reachable) - #162180 (remove outdated next-solver handling) - #162191 (core: mark float `ClampBounds` methods as `#[inline]`) - #162195 (docs(time): clarify exact seconds for week and day) - #162199 (docs(time): clarify exact seconds for hour and minute) - #162222 (coverage: Small cleanups in `extract_hir_info`) - #162230 (Pass -Z merge-functions=disabled in tests/codegen-llvm/intrinsics/unchecked_math.rs)

Rollup merge of #161227 - folkertdev:complex-add-sub, r=nia-e implement `Add` and `Sub` for `Complex` tracking issue: #154023 Adds the `Add` and `Sub` implementations described in the tracking issue. Some notes - I also added a derive for `Eq`, which is useful for `Complex<{integer}>` - The versions that add/sub by a scalar need a `Copy` bound. That seems fine for most actual use cases. Apparently `num_complex` will `Clone` in these operations https://docs.rs/num-complex/latest/num_complex/struct.Complex.html#impl-Add%3CT%3E-for-%26Complex%3CT%3E, but that seems unlike `core` to me. Anyhow, libs can re-litigate that later.

folkertdev added the F-complex_numbers `#![feature(complex_numbers)]` label Aug 17, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Aug 17, 2026

rustbot assigned JohnTitor Aug 17, 2026

beetrees reviewed Aug 17, 2026

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folkertdev force-pushed the complex-add-sub branch 2 times, most recently from b05c4a3 to 5e3bab3 Compare August 17, 2026 19:31

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btnlq reviewed Aug 18, 2026

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folkertdev force-pushed the complex-add-sub branch from 5e3bab3 to fb56ea5 Compare August 18, 2026 09:52

implement Add and Sub for Complex

d48bdef

folkertdev force-pushed the complex-add-sub branch from fb56ea5 to d48bdef Compare August 20, 2026 21:06

folkertdev mentioned this pull request Aug 23, 2026

C interop: Complex<T> rust-lang/goals#761

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rustbot assigned nia-e and unassigned JohnTitor Aug 25, 2026

scottmcm reviewed Aug 27, 2026

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rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 3, 2026

JonathanBrouwer mentioned this pull request Sep 3, 2026

Rollup of 12 pull requests #162249

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This was referenced Sep 3, 2026

Rollup of 13 pull requests #162251

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Rollup of 12 pull requests #162254

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rust-bors Bot merged commit 93b5d3f into rust-lang:main Sep 4, 2026
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rustbot added this to the 1.100.0 milestone Sep 4, 2026

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