CODEWITHSUNDEEP
rust
Test
Test

Reputation: 1720

Rust Nested Serde Lifetimes?

How does one nest serde-izable structs? I tried the simplest approach and the compiler complained about a lifetime not even in my program ('de).

use serde::{Deserialize, Serialize};

#[derive(Serialize, Deserialize)]
struct A<'a> {
    symbol: &'a str,
}

#[derive(Serialize, Deserialize)]
enum B<'a> {
    A(A<'a>),
}

   Compiling rust_iex_parser v0.1.0 (...filename...)
error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'de` due to conflicting requirements
  --> src/test.rs:8:21
   |
8  | #[derive(Serialize, Deserialize)]
   |                     ^^^^^^^^^^^
   |
note: first, the lifetime cannot outlive the lifetime `'de` as defined here...
  --> src/test.rs:8:21
   |
8  | #[derive(Serialize, Deserialize)]
   |                     ^^^^^^^^^^^
note: ...so that the types are compatible
  --> src/test.rs:8:21
   |
8  | #[derive(Serialize, Deserialize)]
   |                     ^^^^^^^^^^^
   = note: expected `EnumAccess<'_>`
              found `EnumAccess<'de>`
note: but, the lifetime must be valid for the lifetime `'a` as defined here...
  --> src/test.rs:9:8
   |
9  | enum B<'a> {
   |        ^^
note: ...so that the types are compatible
  --> src/test.rs:10:7
   |
10 |     A(A<'a>),
   |       ^
   = note: expected `<A<'a> as Deserialize<'_>>`
              found `<A<'_> as Deserialize<'_>>`
   = note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

Upvotes: 0

Views: 285

Answers (1)

Chayim Friedman
Chayim Friedman

Reputation: 71300

For field types other than &[u8] and &str, that involves lifetimes, you have to annotate them with #[serde(borrow)]. See Understanding deserializer lifetimes - Borrowing data in a derived impl:

use serde::{Deserialize, Serialize};

#[derive(Serialize, Deserialize)]
struct A<'a> {
    symbol: &'a str,
}

#[derive(Serialize, Deserialize)]
enum B<'a> {
    #[serde(borrow)]
    A(A<'a>),
}

Playground.

Upvotes: 1

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