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      1 // Copyright (C) 2024 Free Software Foundation, Inc.
      2 
      3 // This program is free software; you can redistribute it and/or modify
      4 // it under the terms of the GNU General Public License as published by
      5 // the Free Software Foundation; either version 3 of the License, or
      6 // (at your option) any later version.
      7 //
      8 // This program is distributed in the hope that it will be useful,
      9 // but WITHOUT ANY WARRANTY; without even the implied warranty of
     10 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     11 // GNU General Public License for more details.
     12 //
     13 // You should have received a copy of the GNU General Public License
     14 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
     15 
     16 #![allow(dead_code)]
     17 #![allow(unused_variables)]
     18 #![allow(unused_assignments)]
     19 
     20 fn ignore<T>(x: T) { }
     21 
     22 // A generic struct that is unsized if T is unsized.
     23 pub struct MaybeUnsizedStruct<T: ?Sized> {
     24     pub regular: u32,
     25     pub rest: T,
     26 }
     27 
     28 // Same but without an ordinary part.
     29 pub struct MaybeUnsizedStruct2<T: ?Sized> {
     30     value: T,
     31 }
     32 
     33 fn main() {
     34     // This struct is still sized because T is a fixed-length array
     35     let sized_struct = &MaybeUnsizedStruct {
     36         regular: 23,
     37         rest: [5, 6, 7],
     38     };
     39 
     40     // This struct is still sized because T is sized
     41     let nested_sized_struct = &MaybeUnsizedStruct {
     42         regular: 91,
     43         rest: MaybeUnsizedStruct {
     44             regular: 23,
     45             rest: [5, 6, 7],
     46         },
     47     };
     48 
     49     // This will be a fat pointer, containing the length of the final
     50     // field.
     51     let unsized_struct: &MaybeUnsizedStruct<[u32]> = sized_struct;
     52 
     53     // This will also be a fat pointer, containing the length of the
     54     // final field.
     55     let nested_unsized_struct:
     56         &MaybeUnsizedStruct<MaybeUnsizedStruct<[u32]>> = nested_sized_struct;
     57 
     58     let alpha: MaybeUnsizedStruct2<[u8; 4]> = MaybeUnsizedStruct2 { value: *b"abc\0" };
     59     let beta: &MaybeUnsizedStruct2<[u8]> = &alpha;
     60 
     61     let reference = &unsized_struct;
     62 
     63     ignore(sized_struct); // set breakpoint here
     64     ignore(nested_sized_struct);
     65     ignore(unsized_struct);
     66     ignore(nested_unsized_struct);
     67 }
     68