SE-0176 Enforce Exclusive Access to Memory
(https://github.com/apple/swift-evolution/blob/master/proposals/0176-enforce-exclusive-access-to-memory.md)
states that "Accesses to different stored properties of a struct or different
elements of a tuple are allowed to overlap."
And indeed this compiles and runs as expected (Xcode 9 beta 4):
// main.swift
func foo() {
var tuple = (1, 2)
swap(&tuple.0, &tuple.1)
print(tuple)
}
foo()
However, if the tuple is a global variable, it crashes with a runtime exception:
// main.swift
var tuple = (1, 2)
swap(&tuple.0, &tuple.1)
print(tuple)
Simultaneous accesses to 0x100401cb0, but modification requires exclusive
access.
Previous access (a modification) started at tupleaccess`main + 76
(0x1000015cc).
Current access (a modification) started at:
0 tupleaccess 0x0000000100335b60
swift_beginAccess + 605
1 tupleaccess 0x0000000100001580 main + 110
2 libdyld.dylib 0x00007fffa7284234 start + 1
Is there anything special with simultaneous access to members of a global
tuple, or is this a bug?
Regards, Martin
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