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[SR-14386] Decimal conformance to FloatingPoint #4216

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swift-ci opened this issue Mar 22, 2021 · 4 comments
Closed

[SR-14386] Decimal conformance to FloatingPoint #4216

swift-ci opened this issue Mar 22, 2021 · 4 comments
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@stephentyrone
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Foundation New Feature

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@swift-ci
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Previous ID SR-14386
Radar rdar://problem/75696891
Original Reporter ken (JIRA User)
Type New Feature
Status Resolved
Resolution Won't Do
Additional Detail from JIRA
Votes 0
Component/s Foundation
Labels New Feature
Assignee @stephentyrone
Priority Medium

md5: d1384030a82997f828586050fabcfc76

Issue Description:

The FloatingPoint protocol is flexible enough to allow radix-10 storage. (BinaryFloatingPoint has the radix-2-specific parts.) Decimal isn't-a FloatingPoint, though its public interface shares a great deal of similarity with FloatingPoint. It even implements parts of FloatingPoint which make no sense on their own, like "isInfinite" and "isSignalingNaN".

It looks like FloatingPoint conformance was the plan:

> Decimal.signalingNaN
error: repl.swift:5:9: error: 'signalingNaN' is unavailable: Decimal does not yet fully adopt FloatingPoint.
Decimal.signalingNaN
        ^~~~~~~~~~~~

Foundation.Decimal:10:23: note: 'signalingNaN' has been explicitly marked unavailable here
    public static var signalingNaN: Decimal { get }
                      ^

I see a few bug reports for individual pieces of this (like SR-8173), but nothing for the whole shebang.
@typesanitizer
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@xAlien95
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FWIW, GSoC-2021 Decimal arithmetic project idea (mentored by @stephentyrone) specifies a new DecimalFloatingPoint protocol mirroring BinaryFloatingPoint.

@stephentyrone
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Foundation.Decimal cannot conform to FloatingPoint because its semantics are penned in by choices that predate Swift (and predate the IEEE 754 Decimal formats). It mirrors the FloatingPoint protocol where possible, but that's the best it can do.

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Comment by Ken Harris (JIRA)

Can the error messages at least be changed to not say "does not yet fully adopt FloatingPoint", if that isn't actually the plan?

It's awfully misleading for an API to "mirror" an existing protocol, but not implement it fully, or correctly, or compatibly – and make it sound like it will conform someday.

Is Decimal deprecated?

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
@shahmishal shahmishal transferred this issue from apple/swift May 5, 2022
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