4 ms·

Most deserializers in typed languages allow you to deserialize straight into structs or typed objects... Serde just doesn't use reflection to do it.

Taywee 5y ago
C++ isn't super easy about it, though. The best C++ json library (in my opinion), nlohmann's json, still requires you to define to_json and from_json for your types to use them. It's not too bad as a one-off, but when you have dozens of types, it gets really tedious compared to Serde, and managing std::variant with it is way more annoying than Serde with Rust enums.
Jweb_Guru 5y ago
APIs like GSON and Jackson have a lot more footguns, because (1) they attempt to (de)serialize types whether or not they were ever intended to be (de)serialized, (2) they are missing information about important constraints due to losing information at runtime (the excuse usually used here is that "they don't do validation" when in reality they are violating expectations of package modularity and encapsulation in a pretty blunt way). For example, they will happily ignore non-null constraints on your fields. In practice, this is a major annoyance and ends up making you very paranoid about (de)serializing any structure you don't have full control over. Performance of a lot of the reflection-based parsing APIs also leaves something to be desired, which means that projects with more stringent performance requirements often have to resort to stuff like Avro. This still happens with serde, but much more rarely--besides having more compile-time information at its disposal and needing to allocate less, it also provides relatively straightforward hooks to achieve things like zero-copy deserialization for strings where the whole buffer is available at once.
- dcow 5y ago
  I’m pretty sure the non-null issue is fixable with a single config option, at least in GSON IIRC.
  - Jweb_Guru 5y ago
    I don't believe it's fixable at all if you're using someone's third-party library that wasn't designed for GSON (unless something has changed a lot since I last used it). The annotation has to be stuck on the original field, AFAIK. And similar stuff apply to other invariants on the type. I believe these kinds of issues are somewhat fundamental when you decide you're going to start (de)serializing structures that never thought about whether or how they'd like that to happen.
    - unnah 5y ago
      In Jackson, you can use mixin classes to define annotations for 3rd party libraries.

Taywee 5y ago

C++ isn't super easy about it, though. The best C++ json library (in my opinion), nlohmann's json, still requires you to define to_json and from_json for your types to use them. It's not too bad as a one-off, but when you have dozens of types, it gets really tedious compared to Serde, and managing std::variant with it is way more annoying than Serde with Rust enums.

Jweb_Guru 5y ago

APIs like GSON and Jackson have a lot more footguns, because (1) they attempt to (de)serialize types whether or not they were ever intended to be (de)serialized, (2) they are missing information about important constraints due to losing information at runtime (the excuse usually used here is that "they don't do validation" when in reality they are violating expectations of package modularity and encapsulation in a pretty blunt way). For example, they will happily ignore non-null constraints on your fields. In practice, this is a major annoyance and ends up making you very paranoid about (de)serializing any structure you don't have full control over. Performance of a lot of the reflection-based parsing APIs also leaves something to be desired, which means that projects with more stringent performance requirements often have to resort to stuff like Avro. This still happens with serde, but much more rarely--besides having more compile-time information at its disposal and needing to allocate less, it also provides relatively straightforward hooks to achieve things like zero-copy deserialization for strings where the whole buffer is available at once.

dcow 5y ago
I’m pretty sure the non-null issue is fixable with a single config option, at least in GSON IIRC.
- Jweb_Guru 5y ago
  I don't believe it's fixable at all if you're using someone's third-party library that wasn't designed for GSON (unless something has changed a lot since I last used it). The annotation has to be stuck on the original field, AFAIK. And similar stuff apply to other invariants on the type. I believe these kinds of issues are somewhat fundamental when you decide you're going to start (de)serializing structures that never thought about whether or how they'd like that to happen.
  - unnah 5y ago
    In Jackson, you can use mixin classes to define annotations for 3rd party libraries.