On Friday, 28 June 2013 at 15:17:12 UTC, monarch_dodra wrote:
Should I have expected a different behavior?
import std.stdio;
int callme()
{
throw new Exception("");
}
struct S
{
int i = 0;
this(int i){this.i = i; writeln("constructing: ", i);}
this(this){writeln("postbliting: ", i);}
~this(){writeln("destroying: ", i);}
}
void foo(S s, int i)
{
s.i = 2;
}
void main()
{
S s = S(1);
foo(s, callme());
}
Destructor for copied object is not called because it is placed
in foo(). Before calling foo(), dmd makes a copy of main.s, calls
postblit, then puts code to invoke callme() and code to invoke
foo(). Since callme() throws, foo() is not called and destructor
placed in foo() is also not called. A struct copy escapes
destructor.
Now, if you try fix this by putting dtor for copy not in foo(),
but in main immediately after foo() invocation, you will have a
problem because destructor would get S(1) object while it should
destroy S(2). Any modification made in foo() is lost. This can be
possible fixed by passing copy by reference which would probably
create new ABI problems.