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Pointwise addition (and multiplication) for array struct members? #342

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matthiasgoergens opened this issue Mar 20, 2024 · 3 comments · May be fixed by #343
Open

Pointwise addition (and multiplication) for array struct members? #342

matthiasgoergens opened this issue Mar 20, 2024 · 3 comments · May be fixed by #343
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@matthiasgoergens
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enhancement
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2.1.0

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@matthiasgoergens
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matthiasgoergens commented Mar 20, 2024 •
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Could we make point-wise addition (and multiplication etc) work for structs (and enums etc) that contain arrays as well?

#[derive(Add)]
struct<T> MyStruct {
    x: [T; 32],
    y: T,
}

At the moment, this fails.

We have a similar failure for tuples:

#[derive(Add)]
struct PointArray {
    a: i32,
    xy: (i32, i32),
    z: i32,
}
matthiasgoergens added a commit to matthiasgoergens/derive_more that referenced this issue Mar 20, 2024
@matthiasgoergens
Support pointwise addition for arrays and tuples
2777c6e 
Fixes JelteF#342

We want to support examples like these:

```rust
struct StructRecursive {
    a: i32,
    b: [i32; 2],
    c: [[i32; 2]; 3],
    d: (i32, i32),
    e: ((u8, [i32; 3]), i32),
    f: ((u8, i32), (u8, ((i32, u64, ((u8, u8), u16)), u8))),
    g: i32,
}

struct TupleRecursive((i32, u8), [(i32, u8); 10]);
```

Supporting arrays and tuples inside of enums would also be useful, but
that's not in this PR.
@matthiasgoergens matthiasgoergens linked a pull request Mar 20, 2024 that will close this issue
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matthiasgoergens added a commit to matthiasgoergens/derive_more that referenced this issue Mar 20, 2024
@matthiasgoergens
Support pointwise addition for arrays and tuples
9250753 
Fixes JelteF#342

We want to support examples like these:

```rust
struct StructRecursive {
    a: i32,
    b: [i32; 2],
    c: [[i32; 2]; 3],
    d: (i32, i32),
    e: ((u8, [i32; 3]), i32),
    f: ((u8, i32), (u8, ((i32, u64, ((u8, u8), u16)), u8))),
    g: i32,
}

struct TupleRecursive((i32, u8), [(i32, u8); 10]);
```

Supporting arrays and tuples inside of enums would also be useful, but
that's not in this PR.
@tyranron
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@matthiasgoergens the tuple case (i32, i32) seems OK, but I'm unsure about the array case [T; 32]. It's not obvious why the Add semantics on array is by-element adding, and not the arrays concatenation.

@JelteF what do you think on this?

@JelteF
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JelteF commented Mar 20, 2024

tl;dr +1 on the idea

Concatenation seems impossible to do to me without returning a different type from Add. So while I also think concatenation is an equally valid Add implementation, I don't think that one could ever be achieved by using derive_more. So having the element-wise addition, seems fine.

And even if we ever figured out how to implement concatenation, we could still add a special attribute to choose between the two.

@matthiasgoergens
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matthiasgoergens commented Mar 20, 2024 •
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Yes, because of the types, point-wise addition is the only thing that makes sense for fixed length arrays.

Have a look at the linked PR for an implementation prototype (with some caveats as noted in my comment.)

Perhaps going with the initial approach, but explicitly adding a Copy constraint in the impl, when the struct contains an array, might be fine? Copy is pretty much mandatory for using Add and Mul etc anyway.

@tyranron tyranron added this to the 1.0.0 milestone Mar 26, 2024
@JelteF JelteF modified the milestones: 1.0.0, 1.1.0 Jul 1, 2024
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Support pointwise addition for arrays and tuples matthiasgoergens/derive_more
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@matthiasgoergens @JelteF @tyranron