Hi,

According to the docs: https://dlang.org/spec/memory-safe-d.html

> Memory-safe code cannot use certain language features, such as:
>
>    Casts that break the type system.
>    Modification of pointer values.
>    Taking the address of a local variable or function parameter.

So, modification of pointer values is prohibited (if I understand this sentence correctly).
However, this code compiles (and will cause a segfault of course): https://run.dlang.io/is/HrUKMy

    import std.stdio;

    @safe void main()
    {
        int *a;
        *a = 10;

        writeln(a);
    }

I'm still learning D so very likely misunderstood something, but isn't that a bug?

Thanks!

On Saturday, 8 September 2018 at 17:01:33 UTC, Jacob Shtokolov wrote:
> So, modification of pointer values is prohibited (if I understand this sentence correctly).

@safe code can't manipulate the pointer itself, in order to avoid memory corruption.

So this is forbidden:

void main() @safe
{
  int* p = malloc(512);
  p++;
}

But in @safe code, the compiler assumes that all pointers you receive are valid. And the null pointer is also valid -- dereferencing it results in a segmentation fault rather than memory corruption.

On Saturday, September 8, 2018 11:06:20 AM MDT Neia Neutuladh via Digitalmars-d wrote:
> On Saturday, 8 September 2018 at 17:01:33 UTC, Jacob Shtokolov
>
> wrote:
> > So, modification of pointer values is prohibited (if I
> > understand this sentence correctly).
>
> @safe code can't manipulate the pointer itself, in order to avoid memory corruption.
>
> So this is forbidden:
>
> void main() @safe
> {
>    int* p = malloc(512);
>    p++;
> }
>
> But in @safe code, the compiler assumes that all pointers you receive are valid. And the null pointer is also valid -- dereferencing it results in a segmentation fault rather than memory corruption.

Also, mutating the data that a pointer points to is not mutating the pointer. So,

*foo = 42;

is not mutating a pointer, whereas

++foo;

would be. So, the first is allowed in @safe code, whereas the second is not.

BTW, if you have questions about D, please ask them in D.Learn. This newsgroup / mailing list / forum is intended for general discussion on D, not for answering questions about how the language works.

- Jonathan M Davis