Derive Macro shredder::Scan

#[derive(Scan)]
{
    // Attributes available to this derive:
    #[shredder]
}

The Scan derive, powering #[derive(Scan)]. Important details here!

Doing #[derive(Scan)] will in fact derive Scan. However, it actually can auto-implement four traits:

• Scan (automatic) [requires all fields be Scan]
• GcSafe (automatic) [requires all fields be GcSafe]
• GcDrop (opt-out) [requires all fields be GcDrop]
• GcDeref(opt-in) [requires all fields be GcDeref]

Scan and GcSafe are the fundamental things that this derive implements. There is no way to opt out.

To opt out of GcDrop, supply the cant_drop flag. Ex:

use shredder::DerefGc;
use shredder::Scan;

#[derive(Scan)]
#[shredder(cant_drop)]
struct WontBeDrop {
    v: DerefGc<u32>
}

To opt into GcDeref, supply the can_deref flag:

use shredder::DerefGc;
use shredder::Scan;

#[derive(Scan)]
#[shredder(can_deref, cant_drop)]
struct WillBeDeref {
    v: DerefGc<u32>
}

Now there are also field flags, which will remove the recursive checks for that trait:

• skip_scan (skips check for Scan)
• unsafe_skip_gc_deref (skips check for GcDeref. Unsafe!)
• unsafe_skip_gc_drop (skips check for GcDrop. Unsafe!)
• unsafe_skip_gc_safe (skips check for GcSafe. Unsafe!)
• unsafe_skip_all (skips check for all traits. Unsafe!)

For safety, if you use unsafe flags, you must ensure those fields satisfy the trait requirements anyway.

Here is an example of skip usage

use shredder::DerefGc;
use shredder::Scan;

#[derive(Scan)]
struct WillBeDeref {
    #[shredder(skip_scan, unsafe_skip_gc_safe, unsafe_skip_gc_drop)]
    v: *const u32 // Assume this is always a valid ptr
}