On Friday, 25 January 2019 at 19:08:55 UTC, Walter Bright wrote:
On 1/25/2019 2:57 AM, kinke wrote:
On Thursday, 24 January 2019 at 23:59:30 UTC, Walter Bright
wrote:
On 1/24/2019 1:03 PM, kinke wrote:
(bool __gate = false;) , ((A __pfx = a();)) , ((B __pfy =
b();)) , __gate = true , f(__pfx, __pfy);
There must be an individual gate for each of __pfx and pfy.
With the rewrite above, if b() throws then _pfx won't be
destructed.
There is no individual gate, there's just one to rule the
caller-destruction of all temporaries.
What happens, then, when b() throws?
`__pfx` goes out of scope, and is dtor expression
(cleanup/finally) is run as part of stack unwinding. Rewritten as
block statement:
{
bool __gate = false;
A __pfx = a();
try {
B __pfy = b(); // may throw
__gate = true;
return f(__pfx, __pfy); // move args to callee
} finally {
__gate || __pfx.__xdtor(); // only destruct if not moved to
callee
}
}
With this DIP, the g() call (both rvalue args passed by ref)
would now become:
{
A __pfx = a();
try {
B __pfy = b(); // may throw
try {
return g(__pfx, __pfy); // pass by ref
} finally {
__pfy.__xdtor(); // always destructed by caller
}
} finally {
__pfx.__xdtor();
}
}
