serde_closure 0.2.3

Serializable and debuggable closures. This library provides macros that wrap closures to make them serializable and debuggable.
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serde_closure

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Serializable and debuggable closures.

This library provides macros that wrap closures to make them serializable and debuggable.

let one = 1;
let plus_one = Fn!(|x: i32| x + one);

assert_eq!(2, plus_one(1));
println!("{:#?}", plus_one);

// prints:
// Fn<main::{{closure}} at main.rs:6:15> {
//     one: 1,
//     source: "| x : i32 | x + one",
// }

This library aims to work in as simple and safe a way as possible. It currently requires nightly Rust for the unboxed_closures and fn_traits features (rust issue #29625).

  • There are three macros, FnOnce, FnMut and Fn, corresponding to the three types of Rust closure.
  • Wrap your closure with one of the macros and it will now implement Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Serialize, Deserialize and Debug.
  • There are some minor syntax limitations, which are documented below.
  • This crate has one unavoidable but documented and sound usage of unsafe.

Examples of wrapped closures

Inferred, non-capturing closure:

|a| a+1

FnMut!(|a| a+1)

Annotated, non-capturing closure:

|a: String| -> String { a.to_uppercase() }

FnMut!(|a: String| -> String { a.to_uppercase() })

Inferred closure, capturing num:

let mut num = 0;
|a| num += a

let mut num = 0;
FnMut!(|a| num += a)

move closure, capturing hello and world:

let hello = String::from("hello");
let mut world = String::new();
move |name| {
    world += (hello.to_uppercase() + name).as_str();
}

let hello = String::from("hello");
let mut world = String::new();
FnMut!(move |name| {
    world += (hello.to_uppercase() + name).as_str();
})

Limitations

There are currently some minor limitations:

  • Captured variables with an uppercase first letter need to be explicitly captured. If you see a panic like the following, fix the case of the variable.
thread 'main' panicked at 'A variable with an upper case first letter was implicitly captured.
Unfortunately due to current limitations it must be captured explicitly.
Please refer to the README.', tests/test.rs:205:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
  • Functions called inside the closure might need to be disambiguated. This also affects enum unit and tuple variants with a lowercase first letter. If you see an error like either of the following, qualify my_function as self::my_function and my_enum_variant as MyEnum::my_enum_variant.
error[E0277]: the trait bound `fn(usize) -> std::option::Option<usize> {my_function::<usize>}: fnref::_IMPL_DESERIALIZE_FOR_Fn::_serde::Serialize` is not satisfied
   --> tests/test.rs:327:10
    |
314 |     fn unfold<A, St, F>(initial_state: St, f: F) -> Unfold<St, F>
    |        ------
315 |     where
316 |         F: Fn(&mut St) -> Option<A> + Serialize,
    |                                       --------- required by this bound in `fnref::unfold`
...
327 |     let _ = unfold(0_usize, Fn!(|acc: &mut _| my_function(*acc)));
    |             ^^^^^^ the trait `fnref::_IMPL_DESERIALIZE_FOR_Fn::_serde::Serialize` is not implemented for `fn(usize) -> std::option::Option<usize> {my_function::<usize>}`

error[E0530]: function parameters cannot shadow tuple variants
   --> tests/test.rs:173:47
    |
173 |     FnMut!(|acc: &mut _| my_enum_variant(*acc))
    |     ---------------------^^^^^^^^^^^^^^^-------
    |     |                    |
    |     |                    cannot be named the same as a tuple variant
    |     in this macro invocation

Serializing between processes

Closures created by this crate are unnameable – i.e. just like normal closures, there is no Rust syntax available with which to write the type. What this means is that to deserialize a closure, you either need to specify the precise type you're deserializing without naming it (which is possible but not particularly practical), or erase the type by storing it in a trait object.

The serde_traitobject crate enables trait objects to be safely serialized and sent between other processes running the same binary.

For example, if you have multiple forks of a process, or the same binary running on each of a cluster of machines, serde_traitobject would help you to send serializable closures between them.

License

Licensed under either of

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.