Bug 20135 – Tuple assignment incorrectly calls destructor on freshly postblitted structs

Tested on dmd.2.088.0-beta.1, but also present on older versions I tried, so I don't think it is new. Consider the following code: -------------- import std.stdio; struct Test { string s; this(string s) { this.s = s; } this(this) { this.s ~= " postblitted"; } ~this() { this.s = "destroyed"; } } struct Wrapper { Test s; } void bug(Ranges...)(Ranges _ranges) { auto ranges = _ranges; // notice how in the original, we can still see the "1" in there writeln(_ranges[0]); // but in the copy made from the tuple assignment above, the destructor // has apparently been run on the new object, starts with "destroyed" writeln(ranges[0]); assert(ranges[0].s.s[0 .. "destroyed".length] != "destroyed"); // fails // same thing happens to ranges[1] btw } void main() { Wrapper a = Wrapper(Test("1")); Wrapper b = Wrapper(Test("2")); bug(a, b); } ------------------ The `ranges = _ranges` does everything right - copies the bits, calls the postblit.... then immediately calls the destructor on the freshly postblitted object, leaving s == "destroyed". (then the writeln adds a bunch of other postblits to it, but once it is destroyed, the relevant data is lost and we are in bug city.) This is reduced from a case an IRC user brought up trying to lockstep over some phobos Files.

Specifically I'd like to thank Nick Rozinsky on IRC for being the one who provided the initial report to me.

*** This issue has been marked as a duplicate of issue 24010 ***