Use Optional Chaining (?.) #4
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**The optional chaining operator returns the value of an object property when the object is available and `undefined` otherwise.** `.?` is similar to the standard `.` chaining operator, with an added check if the object is defined. The optional chaining operator enables you to **write concise and safe chains of connected objects** when some of those objects can be `null` or `undefined`. Before the introduction of optional chaining in ES2020, the `&&` operator was often used to check if an object is available (`obj && obj.value`). This refactoring simplifies existing checks to use the optional chaining pattern: * `x && x.a` becomes `x?.a` * `x != null && x.a` becomes `x?.a` * `x !== null && x !== undefined && x.a` becomes `x?.a` * `x && x.a && x.a.b && x.a.b.c && x.a.b.c.d` becomes `x?.a?.b?.c?.d` * etc. Learn More: [Optional Chaining (MDN)](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining) **The refactoring replaces falsy checks with nullish checks.** For example, when `a && a.b` is replaced with `a?.b`, it changes the execution for certain types, e.g. the empty string `""` is falsy but not nullish. However, in many cases these semantic changes will lead actually to more correct behavior. For example, `text && text.length` will return the empty string, but not its length, whereas `text?.length` will return `0` for the empty string. Learn more: [Truthy (MDN)](https://developer.mozilla.org/en-US/docs/Glossary/Truthy), [Falsy (MDN)](https://developer.mozilla.org/en-US/docs/Glossary/Falsy), [Nullish (MDN)](https://developer.mozilla.org/en-US/docs/Glossary/Nullish) **This refactoring can affects the number of calls made to methods with side effects.** For example, the refactoring changes: ```javascript let a = x() != null && x().a; ``` into ```javascript let a = x()?.a; ``` If `f(1)` has a side effect, it would have been called one or two 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.
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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
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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>
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The optional chaining operator returns the value of an object property when the object is available and
undefinedotherwise..?is similar to the standard.chaining operator, with an added check if the object is defined.The optional chaining operator enables you to write concise and safe chains of connected objects when some of those objects can be
nullorundefined.Before the introduction of optional chaining in ES2020, the
&&operator was often used to check if an object is available (obj && obj.value).This refactoring simplifies existing checks to use the optional chaining pattern:
x && x.abecomesx?.ax != null && x.abecomesx?.ax !== null && x !== undefined && x.abecomesx?.ax && x.a && x.a.b && x.a.b.c && x.a.b.c.dbecomesx?.a?.b?.c?.dLearn More: Optional Chaining (MDN)
The refactoring replaces falsy checks with nullish checks.
For example, when
a && a.bis replaced witha?.b, it changes the execution for certain types, e.g. the empty string""is falsy but not nullish.However, in many cases these semantic changes will lead actually to more correct behavior.
For example,
text && text.lengthwill return the empty string, but not its length, whereastext?.lengthwill return0for the empty string.Learn more: Truthy (MDN), Falsy (MDN), Nullish (MDN)
This refactoring can affects the number of calls made to methods with side effects.
For example, the refactoring changes:
into
If
f(1)has a side effect, it would have been called one or two 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.