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[C++] Replace shared_ptr creation hack before AppendScalarImpl instantiation #33872

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felipecrv opened this issue Jan 26, 2023 · 0 comments · Fixed by #33866
Closed

[C++] Replace shared_ptr creation hack before AppendScalarImpl instantiation #33872

felipecrv opened this issue Jan 26, 2023 · 0 comments · Fixed by #33866
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Component: C++ Type: enhancement
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12.0.0

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felipecrv commented Jan 26, 2023 •
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Describe the enhancement requested

AppendScalarImpl was created for appending scalars based on a contiguous array of std::shared_ptr<Scalar>, so when a single Scalar reference is passed, a dummy shared_ptr is created before the instantiation of AppendScalarImpl.

  std::shared_ptr<Scalar> shared{const_cast<Scalar*>(&scalar), [](Scalar*) {}};
  return AppendScalarImpl{&shared, &shared + 1, n_repeats, this}.Convert();

This seems non-idiomatic [1] and likely inefficient as a control block needs to be heap-allocated for the shared_ptr. An alternative way (that simplifies AppendScalarImpl as well) is a custom iterator class the wraps the source iterator with an extra dereference operation.

[1] Pointers to shared_ptr as class members set a bad-style precedent

Component(s)

C++
@github-actions github-actions bot mentioned this issue Jan 26, 2023
Merged
@lidavidm lidavidm changed the title Replace shared_ptr creation hack before AppendScalarImpl instantiation [C++] Replace shared_ptr creation hack before AppendScalarImpl instantiation Jan 26, 2023
@lidavidm lidavidm added this to the 12.0.0 milestone Jan 26, 2023
lidavidm pushed a commit that referenced this issue Jan 26, 2023
@felipecrv
GH-33872: [C++] Remove hacky shared_ptr construction in AppendScalar (#…
17ea6fc 
…33866)

`AppendScalarImpl` was created for appending scalars based on a contiguous array of `std::shared_ptr<Scalar>`, so when a single `Scalar` reference is passed, a dummy `shared_ptr` is created before the instantiation of `AppendScalarImpl`.

```cpp
  std::shared_ptr<Scalar> shared{const_cast<Scalar*>(&scalar), [](Scalar*) {}};
  return AppendScalarImpl{&shared, &shared + 1, n_repeats, this}.Convert();
```

This seems non-idiomatic [1] and likely inefficient as a control block needs to be heap-allocated for the `shared_ptr`. An alternative way (that simplifies `AppendScalarImpl` as well) is a custom iterator class the wraps the source iterator with an extra dereference operation.

[1] Pointers to `shared_ptr` as class members set a bad-style precedent

### Component(s)

C++

* Closes: #33872

Authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>
sjperkins pushed a commit to sjperkins/arrow that referenced this issue Feb 10, 2023
@felipecrv @sjperkins
apacheGH-33872: [C++] Remove hacky shared_ptr construction in AppendS…
54cb14d 
…calar (apache#33866)

`AppendScalarImpl` was created for appending scalars based on a contiguous array of `std::shared_ptr<Scalar>`, so when a single `Scalar` reference is passed, a dummy `shared_ptr` is created before the instantiation of `AppendScalarImpl`.

```cpp
  std::shared_ptr<Scalar> shared{const_cast<Scalar*>(&scalar), [](Scalar*) {}};
  return AppendScalarImpl{&shared, &shared + 1, n_repeats, this}.Convert();
```

This seems non-idiomatic [1] and likely inefficient as a control block needs to be heap-allocated for the `shared_ptr`. An alternative way (that simplifies `AppendScalarImpl` as well) is a custom iterator class the wraps the source iterator with an extra dereference operation.

[1] Pointers to `shared_ptr` as class members set a bad-style precedent

### Component(s)

C++

* Closes: apache#33872

Authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>
gringasalpastor pushed a commit to gringasalpastor/arrow that referenced this issue Feb 17, 2023
@felipecrv
apacheGH-33872: [C++] Remove hacky shared_ptr construction in AppendS…
d385c7d 
…calar (apache#33866)

`AppendScalarImpl` was created for appending scalars based on a contiguous array of `std::shared_ptr<Scalar>`, so when a single `Scalar` reference is passed, a dummy `shared_ptr` is created before the instantiation of `AppendScalarImpl`.

```cpp
  std::shared_ptr<Scalar> shared{const_cast<Scalar*>(&scalar), [](Scalar*) {}};
  return AppendScalarImpl{&shared, &shared + 1, n_repeats, this}.Convert();
```

This seems non-idiomatic [1] and likely inefficient as a control block needs to be heap-allocated for the `shared_ptr`. An alternative way (that simplifies `AppendScalarImpl` as well) is a custom iterator class the wraps the source iterator with an extra dereference operation.

[1] Pointers to `shared_ptr` as class members set a bad-style precedent

### Component(s)

C++

* Closes: apache#33872

Authored-by: Felipe Oliveira Carvalho <felipekde@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>
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GH-33872: [C++] Remove hacky shared_ptr construction in AppendScalar felipecrv/arrow
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