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Why can't we use RefCell for recursive data structures?
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Why can't we use RefCell for recursive data structures in Rust?
Invalid:
enum List {
Cons(i32, RefCell<List>),
Nil,
}
Valid:
enum List {
Cons(i32, Rc<List>), // or Box<List>
Nil,
}
rust
edited Jan 6 at 2:37
Shepmaster
162k16332477
asked Jan 3 at 12:37
sidoshisidoshi
4711416
add a comment |
Why can't we use RefCell for recursive data structures in Rust?
Invalid:
enum List {
Cons(i32, RefCell<List>),
Nil,
}
Valid:
enum List {
Cons(i32, Rc<List>), // or Box<List>
Nil,
}
rust
edited Jan 6 at 2:37
Shepmaster
162k16332477
asked Jan 3 at 12:37
sidoshisidoshi
4711416
Is this similar enough to Why are recursive struct types illegal in Rust? that it can be closed as a duplicate?
– trentcl
Jan 3 at 17:12
This question is different. I understand why recursive types are invalid and that we can solve that using indirection. But I assume all smart pointers provide indirection since, after all, they are pointers. So my question is is why doesn't RefCell provide indirection?
– sidoshi
Jan 4 at 4:27
add a comment |
Why can't we use RefCell for recursive data structures in Rust?
Invalid:
enum List {
Cons(i32, RefCell<List>),
Nil,
}
Valid:
enum List {
Cons(i32, Rc<List>), // or Box<List>
Nil,
}
rust
edited Jan 6 at 2:37
Shepmaster
162k16332477
asked Jan 3 at 12:37
sidoshisidoshi
4711416
Why can't we use RefCell for recursive data structures in Rust?
Invalid:
enum List {
Cons(i32, RefCell<List>),
Nil,
}
Valid:
enum List {
Cons(i32, Rc<List>), // or Box<List>
Nil,
}
rust
rust
edited Jan 6 at 2:37
Shepmaster
162k16332477
asked Jan 3 at 12:37
sidoshisidoshi
4711416
edited Jan 6 at 2:37
Shepmaster
162k16332477
asked Jan 3 at 12:37
sidoshisidoshi
4711416
edited Jan 6 at 2:37
Shepmaster
162k16332477
edited Jan 6 at 2:37
Shepmaster
162k16332477
edited Jan 6 at 2:37
Shepmaster
162k16332477
162k16332477
asked Jan 3 at 12:37
sidoshisidoshi
4711416
asked Jan 3 at 12:37
sidoshisidoshi
4711416
asked Jan 3 at 12:37
sidoshisidoshi
4711416
4711416
Is this similar enough to Why are recursive struct types illegal in Rust? that it can be closed as a duplicate?
– trentcl
Jan 3 at 17:12
This question is different. I understand why recursive types are invalid and that we can solve that using indirection. But I assume all smart pointers provide indirection since, after all, they are pointers. So my question is is why doesn't RefCell provide indirection?
– sidoshi
Jan 4 at 4:27
add a comment |
Is this similar enough to Why are recursive struct types illegal in Rust? that it can be closed as a duplicate?
– trentcl
Jan 3 at 17:12
This question is different. I understand why recursive types are invalid and that we can solve that using indirection. But I assume all smart pointers provide indirection since, after all, they are pointers. So my question is is why doesn't RefCell provide indirection?
– sidoshi
Jan 4 at 4:27
Is this similar enough to Why are recursive struct types illegal in Rust? that it can be closed as a duplicate?
– trentcl
Jan 3 at 17:12
Is this similar enough to Why are recursive struct types illegal in Rust? that it can be closed as a duplicate?
– trentcl
Jan 3 at 17:12
This question is different. I understand why recursive types are invalid and that we can solve that using indirection. But I assume all smart pointers provide indirection since, after all, they are pointers. So my question is is why doesn't RefCell provide indirection?
– sidoshi
Jan 4 at 4:27
This question is different. I understand why recursive types are invalid and that we can solve that using indirection. But I assume all smart pointers provide indirection since, after all, they are pointers. So my question is is why doesn't RefCell provide indirection?
– sidoshi
Jan 4 at 4:27
add a comment |
1 Answer
1
active
oldest
votes
RefCell contains the object inside, wrapping it, it's not a heap allocated value. That's why the compiler says "recursive without indirection": RefCell is not an indirection.
Box and Rc, on the other hand, contain a reference to an object allocated somewhere else, and therefore are indirections.
Without an indirection, the List enum ends up being infinite since every Cons contains a full List enum inside its RefCell.
You can not do recursive data structures that contain themselves as values, only as pointers or references.
edited Jan 6 at 2:38
Shepmaster
162k16332477
answered Jan 3 at 12:47
Arkaitz JimenezArkaitz Jimenez
16.2k86395
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
RefCell contains the object inside, wrapping it, it's not a heap allocated value. That's why the compiler says "recursive without indirection": RefCell is not an indirection.
Box and Rc, on the other hand, contain a reference to an object allocated somewhere else, and therefore are indirections.
Without an indirection, the List enum ends up being infinite since every Cons contains a full List enum inside its RefCell.
You can not do recursive data structures that contain themselves as values, only as pointers or references.
edited Jan 6 at 2:38
Shepmaster
162k16332477
answered Jan 3 at 12:47
Arkaitz JimenezArkaitz Jimenez
16.2k86395
add a comment |
RefCell contains the object inside, wrapping it, it's not a heap allocated value. That's why the compiler says "recursive without indirection": RefCell is not an indirection.
Box and Rc, on the other hand, contain a reference to an object allocated somewhere else, and therefore are indirections.
Without an indirection, the List enum ends up being infinite since every Cons contains a full List enum inside its RefCell.
You can not do recursive data structures that contain themselves as values, only as pointers or references.
edited Jan 6 at 2:38
Shepmaster
162k16332477
answered Jan 3 at 12:47
Arkaitz JimenezArkaitz Jimenez
16.2k86395
add a comment |
RefCell contains the object inside, wrapping it, it's not a heap allocated value. That's why the compiler says "recursive without indirection": RefCell is not an indirection.
Box and Rc, on the other hand, contain a reference to an object allocated somewhere else, and therefore are indirections.
Without an indirection, the List enum ends up being infinite since every Cons contains a full List enum inside its RefCell.
You can not do recursive data structures that contain themselves as values, only as pointers or references.
edited Jan 6 at 2:38
Shepmaster
162k16332477
answered Jan 3 at 12:47
Arkaitz JimenezArkaitz Jimenez
16.2k86395
RefCell contains the object inside, wrapping it, it's not a heap allocated value. That's why the compiler says "recursive without indirection": RefCell is not an indirection.
Box and Rc, on the other hand, contain a reference to an object allocated somewhere else, and therefore are indirections.
Without an indirection, the List enum ends up being infinite since every Cons contains a full List enum inside its RefCell.
You can not do recursive data structures that contain themselves as values, only as pointers or references.
edited Jan 6 at 2:38
Shepmaster
162k16332477
answered Jan 3 at 12:47
Arkaitz JimenezArkaitz Jimenez
16.2k86395
edited Jan 6 at 2:38
Shepmaster
162k16332477
edited Jan 6 at 2:38
Shepmaster
162k16332477
edited Jan 6 at 2:38
Shepmaster
162k16332477
162k16332477
answered Jan 3 at 12:47
Arkaitz JimenezArkaitz Jimenez
16.2k86395
answered Jan 3 at 12:47
Arkaitz JimenezArkaitz Jimenez
16.2k86395
answered Jan 3 at 12:47
Arkaitz JimenezArkaitz Jimenez
16.2k86395
16.2k86395
add a comment |
add a comment |
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Is this similar enough to Why are recursive struct types illegal in Rust? that it can be closed as a duplicate?
– trentcl
Jan 3 at 17:12
This question is different. I understand why recursive types are invalid and that we can solve that using indirection. But I assume all smart pointers provide indirection since, after all, they are pointers. So my question is is why doesn't RefCell provide indirection?
– sidoshi
Jan 4 at 4:27