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February 17, 2018 Return value in BetterC mode. | ||||
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Hello! Yesterday I found an interesting issue for myself while I was implementing unique pointer for my project in BetterC. When I was trying to return new instance from a `move` method I got calling of destructor the instance. When the instance is out of scope the calling is happens again. I also see that addresses of an instance that calls destructor are same. That thing doesn't happen when I don't use BetterC mode. Is that bug or feature? Please checkout code https://run.dlang.io/is/m1TRnT and try it in BetterC mode and in usual mode. But if I return result of a constructor directly instead of saving the result to variable and returning the variable from the `move` method I don't see double calling of the same destructor. I. e. ``` auto newObject = Box(this); return newObject; ``` is replaced by ``` return Box(this); ``` So... is that bug or feature? |
February 17, 2018 Re: Return value in BetterC mode. | ||||
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Posted in reply to ANtlord | On Saturday, 17 February 2018 at 07:58:40 UTC, ANtlord wrote: > Hello! > Yesterday I found an interesting issue for myself while I was implementing unique pointer for my project in BetterC. When I was trying to return new instance from a `move` method I got calling of destructor the instance. When the instance is out of scope the calling is happens again. I also see that addresses of an instance that calls destructor are same. > > That thing doesn't happen when I don't use BetterC mode. Is that bug or feature? > Please checkout code https://run.dlang.io/is/m1TRnT and try it in BetterC mode and in usual mode. > > But if I return result of a constructor directly instead of saving the result to variable and returning the variable from the `move` method I don't see double calling of the same destructor. > > I. e. > ``` > auto newObject = Box(this); > return newObject; > ``` > is replaced by > ``` > return Box(this); > ``` > > So... is that bug or feature? Okay, with the glorious help of the compiler-switch `-vcg-ast` I was able to see the source of that weirdness. See also: https://forum.dlang.org/thread/juxihybpqpjycmxiydns@forum.dlang.org It seems that there is always a try-block when the struct has a destructor I reduced your code to: ---- struct S { ~this() {} } S myFunction() { S s = S(); return s; } extern( C) void main(){} ---- transformation of myFunction() with $ dmd -betterC -vcg-ast source/app.d ---- S myFunction() { S s = S(); try { return s; } finally s.~this(); } ---- transformation of myFunction() with $ dmd -vcg-ast source/app.d ---- S myFunction() { S s = S(); try return s; catch(Throwable __o3) { s.~this(); throw __o3; } } ---- sadly I have no good idea how to name the title of that issue :/ |
February 18, 2018 Re: Return value in BetterC mode. | ||||
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Posted in reply to meppl | On Saturday, 17 February 2018 at 13:47:28 UTC, meppl wrote: > On Saturday, 17 February 2018 at 07:58:40 UTC, ANtlord wrote: >> ... > ... > sadly I have no good idea how to name the title of that issue :/ I looked at it again and came up with a title name: https://issues.dlang.org/show_bug.cgi?id=18457 |
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