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_isOptional(type(of:)) Does Not Do What You Think It Does #28994

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Merged
merged 1 commit into from
Jan 6, 2020
Merged

_isOptional(type(of:)) Does Not Do What You Think It Does #28994

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4 changes: 3 additions & 1 deletion stdlib/public/core/OutputStream.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -384,7 +384,9 @@ internal func _print_unlocked<T, TargetStream: TextOutputStream>(
// string. Check for Optional first, before checking protocol
// conformance below, because an Optional value is convertible to a
// protocol if its wrapped type conforms to that protocol.
if _isOptional(type(of: value)) {
// Note: _isOptional doesn't work here when T == Any, hence we
// use a more elaborate formulation:
if _openExistential(type(of: value as Any), do: _isOptional) {
let debugPrintable = value as! CustomDebugStringConvertible
debugPrintable.debugDescription.write(to: &target)
return
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