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[SR-13109] compactMap behaves differently when storing result in an optional variable #55555

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swift-ci opened this issue Jun 29, 2020 · 1 comment
Closed

[SR-13109] compactMap behaves differently when storing result in an optional variable #55555

swift-ci opened this issue Jun 29, 2020 · 1 comment
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. standard library Area: Standard library umbrella

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@swift-ci
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Previous ID SR-13109
Radar None
Original Reporter mishra.shashank35 (JIRA User)
Type Bug
Status Resolved
Resolution Invalid

Attachment: Download

Additional Detail from JIRA
Votes 0
Component/s Standard Library
Labels Bug
Assignee None
Priority Medium

md5: 0cd8401bc530790f3f501949662c68e7

Issue Description:

Consider the following playground code -

//Compact map with optional
let marks = ["86", "45", "thiry six", "76"]
let compactMappedOptional: [Int?] = marks.compactMap{ Int($0) }
print("\(compactMappedOptional)")

Output - [Optional(86), Optional(45), nil, Optional(76)]

Expected Output - [Optional(86), Optional(45), Optional(76)]

compactMap() should return non-optional values only. After casting it to [Int?], getting nil as well.
@CodaFi
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CodaFi commented Jul 3, 2020

Your type annotation on the variable compactMappedOptional is what is leading to this situation. In order for compactMap to yield [Int?], the inner closure must yield Int??.

If we drop the annotation, or give it the type type inference actually assigns it if allowed to fully reconstruct the type - [Int] instead of [Int?] - you get the expected outcome.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. standard library Area: Standard library umbrella
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