Re: Destructor called twice.

[TheFlyingFiddle via Digitalmars-d-learn]

On Sunday, 25 February 2018 at 21:35:33 UTC, ketmar wrote:

add postblit debug prints, and you will see.


I get that it will call the postblit since it creates a temporary.

What I expected though was that.

auto s = S(0).foo(1);

Would become something like:

S s; s.__ctor(0).foo(1);

But maybe this would not be consistent behavior?

I'm wondering why it creates the temporary in the first place.

Re: Destructor called twice.

[ketmar via Digitalmars-d-learn]

add postblit debug prints, and you will see.

Destructor called twice.

[TheFlyingFiddle via Digitalmars-d-learn]

When writing some code to setup properties in a chain function 
manner I ran into some unexpected behavior with destructors.


Example:

struct S {
int a, b;

ref S foo(int b) {
this.b = b;
return this;
}

this(int ab) {
this.a = this.b = ab;
printf("ctor a=%d, b=%d\n", a, b);
}

~this() {
printf("dtor a=%d b=%d\n", a, b);
}


}

void main()
{
auto s0 = S(0).foo(1);
auto s1 = S(1).foo(2).foo(3).foo(4);
auto s2 = S(2);
s2.foo(5).foo(6).foo(7);
}

//Output is
ctor 0
dtor 0 1
ctor 1
dtor 1 4
ctor a=2, b=2
dtor a=2 b=7
dtor 1 4
dtor 0 1


For s0,s1 the destructor is called twice but s2 works as I would 
expect.


Taking a look with dmd -vcg-ast provided this:
void main()
{
S s0 = ((S __slS3 = S(, );) , __slS3).this(0).foo(1);
try
{
	S s1 = ((S __slS4 = S(, );) , 
__slS4).this(1).foo(2).foo(3).foo(4);

try
{
S s2 = s2 = S , s2.this(2);
try
{
s2.foo(5).foo(6).foo(7);
}
finally
s2.~this();
}
finally
s1.~this();
}
finally
s0.~this();
return 0;
}

The two extra dtor calls are not visible here but I guess they 
are caused by the temporary variables that are created and then 
go out of scope directly. Am I doing something wrong or is this a 
bug?