[Dlang-internal] -dip1000 discussion

[Olivier FAURE via Dlang-internal]

On Sunday, 29 January 2017 at 11:45:30 UTC, Walter Bright wrote:
> On 1/29/2017 3:24 AM, Olivier FAURE wrote:
> It's best to post compilable code fragments. This code compiles 
> with -dip1000:

It shouldn't. This is one of the 'gotcha's that I mentioned 
earlier.

     struct Container
     {
         int* ptr;
     }

     ref Container store(ref return scope Container c, return 
scope int* ptr) @safe
     {
         c.ptr = ptr;
         return c;
     }

     Container* foobar() @safe
     {
         Container* c = new Container;
         int x = 42;
         scope int* ptr = &x;

         scope Container c2 = store(*c, ptr);

         return c;
     }

     void main() @safe
     {
         import std.stdio;
         import std.conv;

         int x = *foobar().ptr; // invalid write
     }

This code should not compile, and having a @safe opaque 'store' 
function is not possible with 'return scope' alone unless you use 
the functional programming idiom of returning a new object 
instead of mutating objects passed by reference.