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[string] ARC hack around hashValue #14118

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Merged
merged 1 commit into from
Jan 24, 2018
Merged

[string] ARC hack around hashValue #14118

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20 changes: 18 additions & 2 deletions stdlib/public/core/StringHashable.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -145,9 +145,22 @@ extension _UnmanagedOpaqueString {
}

extension _StringGuts {
//
// FIXME(TODO: JIRA): HACK HACK HACK: Work around for ARC :-(
//
@_versioned
@effects(readonly)
@inline(never) // Hide the CF dependency
internal static func _computeHashValue(
_unsafeBitPattern: _RawBitPattern
) -> Int {
return _StringGuts(rawBits: _unsafeBitPattern)._computeHashValue()
}

@_versioned
// TODO: After removing above hack: @inline(never) // Hide the CF dependency
internal func _computeHashValue() -> Int {
defer { _fixLifetime(self) }
if _slowPath(_isOpaque) {
return _asOpaque().computeHashValue()
}
Expand All @@ -158,8 +171,9 @@ extension _StringGuts {
}

@_versioned
@inline(never) // Hide the CF dependency
// TODO: After removing above hack: @inline(never) // Hide the CF dependency
internal func _computeHashValue(_ range: Range<Int>) -> Int {
defer { _fixLifetime(self) }
if _slowPath(_isOpaque) {
return _asOpaque()[range].computeHashValue()
}
Expand All @@ -177,7 +191,9 @@ extension String : Hashable {
/// your program. Do not save hash values to use during a future execution.
@_inlineable // FIXME(sil-serialize-all)
public var hashValue: Int {
return _guts._computeHashValue()
defer { _fixLifetime(self) }
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Is the _fixLifetime necessary here? If it is, we should audit for missing cases elsewhere; I started eliding it under the assumption that self lifetime is guaranteed.

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Self lifetime is not guaranteed, and technically these are always necessary. _LegacyStringCore violated this rule all over the place, and never blew up, but doing this is a good idea. @atrick was working on a dependent-lifetime improvement wherein we could say that some values/expressions/properties have lifetime dependent on self, and that would alleviate this.

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I think there's some confusion because self has a guaranteed calling convention, which is completely different from a fixed lifetime--it doesn't give you any lifetime guarantee. Currently, the best thing you can do is defer { _fixLifetime }. That's terrible for multiple reasons, but I haven't had any time to introduce a reasonable alternative.

let gutsBits = _guts.rawBits
return _StringGuts._computeHashValue(_unsafeBitPattern: gutsBits)
}
}

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