// --------------------------------------------------------------------------
// This program compiles with eg the default toolchain of Xcode 9.3 beta 4,
// but crashes recent versions of the compiler (for example dev snapshot
// 2018-02-25, 2018-03-13 and 2018-03-17, have only tested those three).
// --------------------------------------------------------------------------
var a: Int? {
    didSet { print("hello") }
}
a? = 123

// --------------------------------------------------------------------------
// Compiling and running with default toolchain of Xcode 9.3 beta 4:
// --------------------------------------------------------------------------
// › swiftc --version
// Apple Swift version 4.1 (swiftlang-902.0.43 clang-902.0.37.1)
// Target: x86_64-apple-darwin17.4.0
// ›
// › swiftc test.swift
// › ./test
// hello
//
// --------------------------------------------------------------------------
// Compiling and running with development snapshot 2018-03-17:
// --------------------------------------------------------------------------
// › /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2018-03-17-a.xctoolchain/usr/bin/swiftc --version
// Apple Swift version 4.2-dev (LLVM cef3fe6d75, Clang bdc970d89c, Swift 931d06d1cc)
// Target: x86_64-apple-darwin17.4.0
// ›
// › /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2018-03-17-a.xctoolchain/usr/bin/swiftc test.swift
// Assertion failed: (value && "No value specified"), function forUnmanaged, file /Users/buildnode/jenkins/workspace/oss-swift-package-osx/swift/lib/SILGen/ManagedValue.h, line 91.
// 0  swift                    0x000000010aaee2c8 llvm::sys::PrintStackTrace(llvm::raw_ostream&) + 40
// 1  swift                    0x000000010aaee9d6 SignalHandler(int) + 694
// 2  libsystem_platform.dylib 0x00007fff6e86df5a _sigtramp + 26
// ...

var x: Int? = 123 {
    willSet {
        print("willSet called:")
        print("    current value: \(String(describing: x))")
        print("        new value: \(String(describing: newValue))")
    }
}
print(String(describing: x))
x?.negate()
print(String(describing: x))