Re: Problem with dmd-2.104.0 -dip1000 & @safe

[Timon Gehr via Digitalmars-d-learn]

On 6/9/23 06:05, An Pham wrote:

Getting with below error for following codes. Look like bug?
onlineapp.d(61): Error: scope variable `a` assigned to non-scope 
parameter `a` calling `foo`


     @safe:

     struct A(S = string)
     {
     @safe:
     S s;
     void delegate() c;
     }

     struct B(S = string)
     {
     @safe:
     @disable this();

     this(C!S c, A!S a)
     {
     this.c = c;
     this.a = a;
     }

     C!S foo()
     {
     return c;
     }

     A!S a;
     C!S c;
     }

     class C(S = string)
     {
     @safe:
     C!S foo(A!S a)
     {
     auto o = new Object();
     return foo2(o, a);
     }

     C!S foo2(Object n, A!S a)
     {
     auto b = B!S(this, a);
  return b.foo();
     }
     }

     unittest
     {
     static struct X
     {
     @safe:
     void foo3()
     {
     }
     }

     X x;
     A!string a;
     a.s = "foo";
     a.c = 
     auto c = new C!string();
     c.foo(a);
     }

void main()
{
}



I think the behavior you are seeing here is by design. There are two 
things happening:


- There is no `scope` inference for virtual methods, as it is impossible 
to get the inference right without knowing all overriding methods in 
advance.


- You cannot mark the parameter `a` `scope`, because the lifetimes of 
`this` and `a` become conflated within `b` in the body of `foo2` when 
calling the constructor of `B!S`, and `this` is subsequently escaped.


As Dennis points out, a workaround is to mark the parameter `a` `return 
scope`. However, this may lead to other problems down the line, as `a` 
is never actually escaped.

Re: Problem with dmd-2.104.0 -dip1000 & @safe

[Dennis via Digitalmars-d-learn]

On Friday, 9 June 2023 at 04:05:27 UTC, An Pham wrote:

Getting with below error for following codes. Look like bug?


Filed as https://issues.dlang.org/show_bug.cgi?id=23985

You can work around it by marking parameter `a` as `return scope`

Problem with dmd-2.104.0 -dip1000 & @safe

[An Pham via Digitalmars-d-learn]

Getting with below error for following codes. Look like bug?
onlineapp.d(61): Error: scope variable `a` assigned to non-scope 
parameter `a` calling `foo`


@safe:

struct A(S = string)
{
@safe:
S s;
void delegate() c;
}

struct B(S = string)
{
@safe:
@disable this();

this(C!S c, A!S a)
{
this.c = c;
this.a = a;
}

C!S foo()
{
return c;
}

A!S a;
C!S c;
}

class C(S = string)
{
@safe:
C!S foo(A!S a)
{
auto o = new Object();
return foo2(o, a);
}

C!S foo2(Object n, A!S a)
{
auto b = B!S(this, a);
return b.foo();
}
}

unittest
{
static struct X
{
@safe:
void foo3()
{
}
}

X x;
A!string a;
a.s = "foo";
a.c = 
auto c = new C!string();
c.foo(a);
}

void main()
{
}