Bug Report: `std::optional<double>` corruption in Release builds

[hyochan]

Summary

Similar to #84848 (bool), std::optional<double> values are also corrupted in Release builds when accessed via Swift/C++ interop. This appears to be the same underlying issue affecting different types.

Environment

• Xcode 16.1.1, Swift 6.0, macOS Sequoia
• iOS Simulator (arm64)

Problem

Accessing std::optional<double> from C++ structs in Swift:

• Debug: Works correctly
• Release: Returns nil, wrong values, or -nan

Example

// C++ struct with std::optional<double> properties
// Input: sampleRate = 22050, channels = 2

// BROKEN in Release:
let rate = config.sampleRate.value  // Returns nil or -nan

// WORKAROUND (works in Release):
let rate = config.sampleRate.has_value() ? config.sampleRate.pointee : nil

Release Build Output

Property	Expected	Actual (Release)
sampleRate	22050.0	nil
channels	2.0	5.0 (wrong!)
bitRate	64000.0	-nan

Reproduction

Real-world repo: react-native-nitro-sound

git clone https://github.com/hyochan/react-native-nitro-sound.git
cd react-native-nitro-sound && yarn install
cd example && pod install && cd ..
yarn workspace react-native-nitro-sound-example build:ios
# Run → Record audio → Check with afinfo
# Expected: 22050 Hz, 2 ch | Actual: 8000 Hz, 1 ch

Notes

• Bug more likely with structs containing many std::optional properties (our struct has 18)
• Same workaround as [cxx-interop] An std::optional<bool>'s .value is always false in Release mode #84848: use .has_value() ? .pointee : nil instead of .value
• Causes runtime crashes when -nan is cast to Int

Related

• [cxx-interop] An std::optional<bool>'s .value is always false in Release mode #84848 (same issue for std::optional<bool>)
• fix: Fix optional doubles not building in Release mode on Swift mrousavy/nitro#1065
• Audio codec properties not respected in release builds on iOS hyochan/react-native-nitro-sound#741