Re: Is there a way to slice non-array type in @safe?

[Paul Backus via Digitalmars-d-learn]

On Thursday, 11 July 2019 at 19:44:51 UTC, Stefanos Baziotis 
wrote:
On Thursday, 11 July 2019 at 19:37:38 UTC, Nathan S. wrote:

If you know that what you're doing cannot result in memory 
corruption but the compiler cannot automatically infer @safe, 
it is appropriate to use @trusted. (For this case make sure 
you're not returning the byte slices, since if the arguments 
were allocated on the stack you could end up with a pointer to 
an invalid stack frame. If it's the caller's responsibility to 
ensure the slice doesn't outlive the struct then it is the 
caller that should be @trusted or not.)

Yes, @trusted is an option. I mean it's a good solution, but 
from the standpoint of the language user, it seems unfortunate 
that for the case static types
@trusted has to be used while the array one can be @safe:

int memcmp(T)(const T[] s1, const T[] s2) @safe
{
    const byte[] s1b = (cast(const(byte[]))s1)[0 .. s1.length * 
T.sizeof];
    const byte[] s2b = (cast(const(byte[]))s2)[0 .. s2.length * 
T.sizeof];
}

You can use a union:

int foo(T)(ref T s1, ref T s2) {
    import std.stdio;

    union U {
        T val;
        byte[T.sizeof] bytes;
    }

    const U s1u = { val: s1 };
    const U s2u = { val: s2 };

    writeln("s1 bytes: ", s1u.bytes);
    writeln("s2 bytes: ", s2u.bytes);

    return 0;
}

@safe void main() {
    double a = 12.345, b = 67.890;
    foo(a, b);
}

However, accessing the `bytes` member will still be considered 
@system if T is or contains a pointer. To fix this, you can use a 
@trusted nested function to do the union access; e.g.,

    @trusted ref const(ubyte[T.sizeof]) getBytes(ref U u) { 
return u.bytes; }
    // ...
    writeln("s1 bytes: ", getBytes(s1u));