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[SR-12093] Checked Casts With Literals Are Deeply Unintuitive #54529

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CodaFi opened this issue Jan 28, 2020 · 5 comments
Open

[SR-12093] Checked Casts With Literals Are Deeply Unintuitive #54529

CodaFi opened this issue Jan 28, 2020 · 5 comments
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casting Feature: explicit casting (is, as, as? and as!) compiler The Swift compiler in itself improvement literals Feature → expressions: Literals such as an integer or string literal swift evolution proposal needed Flag → feature: A feature that warrants a Swift evolution proposal

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@CodaFi
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CodaFi commented Jan 28, 2020

Previous ID SR-12093
Radar rdar://problem/58999135
Original Reporter @CodaFi
Type Improvement
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Improvement, StarterProposal
Assignee inatonix (JIRA)
Priority Medium

md5: f23b80191801a31166f6b799915c7a23

cloned from:

  • SR-11421 Checked Cast Diagnostics Should Be More Specific When Literals Are Involved

Issue Description:

Checked casts on literals can have surprising effects at face value

let character = "A" as Character
let bad = "A" as? Character

The former is a character literal and is statically coerced. The latter is a String literal that is being dynamically cast to a Character. This cast will always fail, and we note as much - this also works with as! force casts.

warning: cast from 'String' to unrelated type 'Character' always fails

This behavior is deeply unintuitive and should be revisited by a proposal to unify casting semantics for literals.
@beccadax
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@swift-ci create

@LucianoPAlmeida
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Just for reference, link to a PR related to the cloned bug #29493

@swift-ci
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swift-ci commented Apr 6, 2020

Comment by shuya inada (JIRA)

Is it okay to tackle on this task? This is my first commit for Swift.

@CodaFi
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CodaFi commented Apr 7, 2020

inatonix (JIRA User) You should know that this might involve a lot of work up front for one's first bug. You'll need to take a look at all the places where we aren't consistent between the static and dynamic coercions, figure out what we're missing, and draw up a proposal that provides a unified and consistent semantics for the two. Then you'll need to implement your proposal and drive it through evolution.

If this still sounds like a path you'd like to pursue, then by all means let me know how I can help. But if you're interest in a separate starter bug recommendation, I can give that too.

@swift-ci
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swift-ci commented Apr 8, 2020

Comment by shuya inada (JIRA)

@CodaFi Thank you for your comment! I got it, this problem sounds pretty difficult as my first task on Swift.. Do you have any recommendation task like separated starter bugs as the first contribution to Swift?

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@AnthonyLatsis AnthonyLatsis added casting Feature: explicit casting (is, as, as? and as!) swift evolution proposal needed Flag → feature: A feature that warrants a Swift evolution proposal literals Feature → expressions: Literals such as an integer or string literal and removed StarterProposal labels Nov 11, 2022
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casting Feature: explicit casting (is, as, as? and as!) compiler The Swift compiler in itself improvement literals Feature → expressions: Literals such as an integer or string literal swift evolution proposal needed Flag → feature: A feature that warrants a Swift evolution proposal
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@beccadax @CodaFi @LucianoPAlmeida @swift-ci @AnthonyLatsis