Use Nullish Coalescing Operator (??) For Defaults #3
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
![p42-ai[bot]](https://avatars.githubusercontent.com/in/83247?s=60&v=4){kind=small}
**The nullish coalescing operator (`??`) returns its right side when its left side is nullish** (`null` or `undefined`), and its left side otherwise. For example, `const x = a ?? b` would set `x` to `a` if `a` has a value, and to `b` if `a` is `null` or `undefined`. The nullish coalescing operator is very useful to **provide default values when a value or an expression is nullish**. Before its introduction in ES2020, this default value pattern was often expressed using the conditional operator. This refactoring simplifies conditional (ternary) checks to nullish coalescing operator expressions: * `a == null ? x : a` becomes `a ?? x` * `a != null ? a : x` becomes `a ?? x` * `a === null || a === undefined ? x : a` becomes `a ?? x` * `a !== null && a !== undefined ? a : x` becomes `a ?? x` * `f(1) != null ? f(1) : x` becomes `f(1) ?? x` * etc. Learn More: [Nullish coalescing operator (MDN)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_operator) When two similar-looking function calls have a side effect, this refactoring can change the behavior of the code. For example, the refactoring changes: ```javascript let a = f(1) === null || f(1) === undefined ? 'default' : f(1); ``` into ```javascript let a = f(1) ?? 'default'; ``` If `f(1)` has a side effect, it would have been called one, two or three times before the refactoring, and once after the refactoring. This means that the side effect would have been called a different number of times, potentially changing the behavior.
|
Thanks for opening a pull request! If this is not a minor PR. Could you open an issue for this pull request on JIRA? https://issues.apache.org/jira/browse/ARROW Opening JIRAs ahead of time contributes to the Openness of the Apache Arrow project. Then could you also rename pull request title in the following format? or See also: |
domoritz
pushed a commit
that referenced
this pull request
Jul 7, 2021
Before change:
```
Direct leak of 65536 byte(s) in 1 object(s) allocated from:
#0 0x522f09 in
#1 0x7f28ae5826f4 in
#2 0x7f28ae57fa5d in
#3 0x7f28ae58cb0f in
#4 0x7f28ae58bda0 in
...
```
After change:
```
Direct leak of 65536 byte(s) in 1 object(s) allocated from:
#0 0x522f09 in posix_memalign (/build/cpp/debug/arrow-dataset-file-csv-test+0x522f09)
#1 0x7f28ae5826f4 in arrow::(anonymous namespace)::SystemAllocator::AllocateAligned(long, unsigned char**) /arrow/cpp/src/arrow/memory_pool.cc:213:24
#2 0x7f28ae57fa5d in arrow::BaseMemoryPoolImpl<arrow::(anonymous namespace)::SystemAllocator>::Allocate(long, unsigned char**) /arrow/cpp/src/arrow/memory_pool.cc:405:5
#3 0x7f28ae58cb0f in arrow::PoolBuffer::Reserve(long) /arrow/cpp/src/arrow/memory_pool.cc:717:9
#4 0x7f28ae58bda0 in arrow::PoolBuffer::Resize(long, bool) /arrow/cpp/src/arrow/memory_pool.cc:741:7
...
```
Closes apache#10498 from westonpace/feature/ARROW-13027--c-fix-asan-stack-traces-in-ci
Authored-by: Weston Pace <weston.pace@gmail.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The nullish coalescing operator (
??) returns its right side when its left side is nullish (nullorundefined), and its left side otherwise.For example,
const x = a ?? bwould setxtoaifahas a value, and tobifaisnullorundefined.The nullish coalescing operator is very useful to provide default values when a value or an expression is nullish.
Before its introduction in ES2020, this default value pattern was often expressed using the conditional operator.
This refactoring simplifies conditional (ternary) checks to nullish coalescing operator expressions:
a == null ? x : abecomesa ?? xa != null ? a : xbecomesa ?? xa === null || a === undefined ? x : abecomesa ?? xa !== null && a !== undefined ? a : xbecomesa ?? xf(1) != null ? f(1) : xbecomesf(1) ?? xLearn More: Nullish coalescing operator (MDN)
When two similar-looking function calls have a side effect, this refactoring can change the behavior of the code.
For example, the refactoring changes:
into
If
f(1)has a side effect, it would have been called one, two or three times before the refactoring, and once after the refactoring.This means that the side effect would have been called a different number of times, potentially changing the behavior.