April 12, 2014 [Issue 12566] New: Give DList true reference semantics | ||||
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https://issues.dlang.org/show_bug.cgi?id=12566 Issue ID: 12566 Summary: Give DList true reference semantics Product: D Version: D2 Hardware: All OS: All Status: NEW Severity: enhancement Priority: P1 Component: Phobos Assignee: nobody@puremagic.com Reporter: monarchdodra@gmail.com DList currently uses some weird semantics. It is neither value nor reference semantics. The behavior is documented, but the documentation is the result of what I think was a buggy behavior to begin with. Issues with the current behavior include: 1. It's surprising. I think *everyone* simply expects reference semantics (or wants value semantics). But they know what to *expect*. Currently, they don't get what they expect: //---- auto a = DList!size_t(1, 2, 3); auto b = a; //Deep copy? Shallow copy? b.removeBack(); assert(!equal(a[], b[])); //different assert(!(a is b)); //different assert(equal(a[], [1, 2, 3])); //a was unchanged. b.insertBack(3); //Put 3 back in. writeln(a[]); //prints [1, 2, 3, 3] assert(equal(a[], [1, 2, 3])); //fails. a was changed. //---- Unless you actually *wrote* DList, I don't think you could really understand *why* this is happening. 2. Data is *never* released: No matter how many time you call "removeBack" or "removeFront", the nodes are never actually excised from the chain. This can lead to a "leak" in the sense that dead data is actually still referenced by live pointers. This program will crawl to a stall and halt: auto d = DList!size_t(1, 1); foreach (k; 0 .. size_t.max - 1) { if (k%100_000 == 0) writeln(k); d.removeBack(); d.insertBack(k); } 3. It's inefficient and buggy. *trivial* use cases are *still* failing: //---- auto dl2 = DList!int([2,7]); dl2.removeFront(); assert(dl2[].walkLength == 1); dl2.removeBack(); assert(dl2.empty, "not empty?!"); //Fails //---- -- |
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