1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
//! Serializable and deserializable trait objects.
//!
//! **[Crates.io](https://crates.io/crates/serde_traitobject) │ [Repo](https://github.com/alecmocatta/serde_traitobject)**
//!
//! This library enables the serialization and deserialization of trait objects so they can be 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, this library lets you send trait objects between them.
//!
//! Any trait can be made (de)serializable when made into a trait object by adding this crate's [Serialize] and [Deserialize] traits as supertraits:
//!
//! ```
//! # use serde_derive::{Serialize, Deserialize};
//! trait MyTrait: serde_traitobject::Serialize + serde_traitobject::Deserialize {
//!     fn my_method(&self);
//! }
//!
//! #[derive(Serialize, Deserialize)]
//! struct Message {
//!     #[serde(with = "serde_traitobject")]
//!     message: Box<dyn MyTrait>,
//! }
//!
//! // Woohoo, `Message` is now serializable!
//! ```
//!
//! And that's it! The two traits are automatically implemented for all `T: serde::Serialize` and all `T: serde::de::DeserializeOwned`, so as long as all implementors of your trait are themselves serializable then you're good to go.
//!
//! There are two ways to (de)serialize your trait object:
//!  * Apply the `#[serde(with = "serde_traitobject")]` [field attribute](https://serde.rs/attributes.html), which instructs serde to use this crate's [serialize](serialize()) and [deserialize](deserialize()) functions;
//!  * The [Box], [Rc] and [Arc] structs, which are simple wrappers around their stdlib counterparts that automatically handle (de)serialization without needing the above annotation;
//!
//! Additionally, there are several convenience traits implemented that extend their stdlib counterparts:
//!
//!  * [Any], [Debug], [Display], [Error], [Fn], [FnMut], [FnOnce]
//!
//! These are automatically implemented on all implementors of their stdlib counterparts that also implement `serde::Serialize` and `serde::de::DeserializeOwned`.
//!
//! ```
//! # use serde_derive::{Serialize, Deserialize};
//! use std::any::Any;
//! use serde_traitobject as s;
//!
//! #[derive(Serialize, Deserialize, Debug)]
//! struct MyStruct {
//!     foo: String,
//!     bar: usize,
//! }
//!
//! let my_struct = MyStruct {
//!     foo: String::from("abc"),
//!     bar: 123,
//! };
//!
//! let erased: s::Box<dyn s::Any> = s::Box::new(my_struct);
//!
//! let serialized = serde_json::to_string(&erased).unwrap();
//! let deserialized: s::Box<dyn s::Any> = serde_json::from_str(&serialized).unwrap();
//!
//! let downcast: Box<MyStruct> = Box::<dyn Any>::downcast(deserialized.into_any()).unwrap();
//!
//! println!("{:?}", downcast);
//! # assert_eq!(format!("{:?}", downcast), "MyStruct { foo: \"abc\", bar: 123 }");
//! // MyStruct { foo: "abc", bar: 123 }
//! ```
//!
//! # Security
//!
//! This crate works by wrapping the vtable pointer with [`relative::Vtable`](https://docs.rs/relative) such that it can safely be sent between processes.
//!
//! This approach is not yet secure against malicious actors. However, if we assume non-malicious actors and typical (static or dynamic) linking conditions, then it's not unreasonable to consider it sound.
//!
//! See [here](https://github.com/rust-lang/rust/pull/66113) for ongoing work in `rustc` to make this safe and secure.
//!
//! ## Validation
//!
//! Three things are serialized alongside the vtable pointer for the purpose of validation:
//!
//!  * the [`build_id`](https://github.com/alecmocatta/build_id) (128 bits);
//!  * the [`type_id`](https://doc.rust-lang.org/std/intrinsics/fn.type_id.html) of the trait object (64 bits);
//!  * the `type_id` of the concrete type (64 bits).
//!
//! At some point in Rust's future, I think it would be great if the latter could be used to safely look up and create a trait object. As it is, that functionality doesn't exist yet, so what this crate does instead is serialize the vtable pointer (relative to a static base), and do as much validity checking as it reasonably can before it can be used and potentially invoke UB.
//!
//! The first two are [checked for validity](https://github.com/alecmocatta/relative/blob/dae206663a09b9c0c4b3012c528b0e9c063df742/src/lib.rs#L457-L474) before usage of the vtable pointer. The `build_id` ensures that the vtable pointer came from an invocation of an identically laid out binary<sup>1</sup>. The `type_id` ensures that the trait object being deserialized is the same type as the trait object that was serialized. They ensure that under non-malicious conditions, attempts to deserialize invalid data return an error rather than UB. The `type_id` of the concrete type is used as a [sanity check](https://github.com/alecmocatta/serde_traitobject/blob/b20d74e183063e7d49aff2eabc9dcd5bc26d7c07/src/lib.rs#L469) that panics if it differs from the `type_id` of the concrete type to be deserialized.
//!
//! Regarding collisions, the 128 bit `build_id` colliding is sufficiently unlikely that it can be relied upon to never occur. The 64 bit `type_id` colliding is possible, see [rust-lang/rust#10389](https://github.com/rust-lang/rust/issues/10389), though exceedingly unlikely to occur in practise.
//!
//! The vtable pointer is (de)serialized as a usize relative to the vtable pointer of [this static trait object](https://github.com/alecmocatta/relative/blob/dae206663a09b9c0c4b3012c528b0e9c063df742/src/lib.rs#L90). This enables it to work under typical dynamic linking conditions, where the absolute vtable addresses can differ across invocations of the same binary, but relative addresses remain constant.
//!
//! All together this leaves, as far as I'm aware, three soundness holes:
//!
//!  * A malicious user with a copy of the binary could trivially craft a `build_id` and `type_id` that pass validation and gives them control of where to jump to.
//!  * Data corruption of the serialized vtable pointer but not the `build_id` or `type_id` used for validation, resulting in a jump to an arbitrary address. This could be rectified in a future version of this library by using a cipher to make it vanishingly unlikely for corruptions to affect only the vtable pointer, by mixing the vtable pointer and validation components upon (de)serialization.
//!  * Dynamic linking conditions where the relative addresses (vtable - static vtable) are different across different invocations of the same binary. I'm sure this is possible, but it's not a scenario I've encountered so I can't speak to its commonness.
//!
//! <sup>1</sup>I don't think this requirement is strictly necessary, as the `type_id` should include all information that could affect soundness (trait methods, calling conventions, etc), but it's included in case that doesn't hold in practise; to provide a more helpful error message; and to reduce the likelihood of collisions.
//!
//! # Note
//!
//! This crate currently requires Rust nightly.

#![doc(html_root_url = "https://docs.rs/serde_traitobject/0.2.7")]
#![feature(
	arbitrary_self_types,
	coerce_unsized,
	fn_traits,
	tuple_trait,
	specialization,
	unboxed_closures,
	unsize
)]
#![warn(
	missing_copy_implementations,
	missing_debug_implementations,
	missing_docs,
	trivial_casts,
	trivial_numeric_casts,
	unused_import_braces,
	unused_qualifications,
	unused_results,
	clippy::pedantic
)] // from https://github.com/rust-unofficial/patterns/blob/master/anti_patterns/deny-warnings.md
#![allow(
	clippy::must_use_candidate,
	clippy::missing_errors_doc,
	incomplete_features
)]

mod convenience;

use metatype::type_coerce;
use relative::Vtable;
use serde::ser::SerializeTuple;
use std::{any::type_name, boxed, fmt, marker};

pub use convenience::*;

/// Any trait with this as a supertrait can be serialized as a trait object.
///
/// It is automatically implemented for all `T: serde::Serialize`, i.e. you should not implement it manually.
///
/// To use, simply add it as a supertrait to your trait:
/// ```
/// use serde_derive::{Serialize, Deserialize};
///
/// trait MyTrait: serde_traitobject::Serialize + serde_traitobject::Deserialize {
///     fn my_method(&self);
/// }
/// ```
///
/// Now your trait object is serializable!
/// ```
/// # use serde_derive::{Serialize, Deserialize};
/// #
/// # trait MyTrait: serde_traitobject::Serialize + serde_traitobject::Deserialize {
/// #     fn my_method(&self);
/// # }
/// #[derive(Serialize, Deserialize)]
/// struct Message(#[serde(with = "serde_traitobject")] Box<dyn MyTrait>);
///
/// // Woohoo, `Message` is now serializable!
/// ```
///
/// Any implementers of `MyTrait` would now have to themselves implement `serde::Serialize` and `serde::de::DeserializeOwned`. This would typically be through `serde_derive`, like:
/// ```
/// # use serde_derive::{Serialize, Deserialize};
/// # trait MyTrait: serde_traitobject::Serialize + serde_traitobject::Deserialize {
/// #     fn my_method(&self);
/// # }
/// # #[derive(Serialize, Deserialize)]
/// # struct Message(#[serde(with = "serde_traitobject")] Box<dyn MyTrait>);
/// #[derive(Serialize, Deserialize)]
/// struct MyStruct {
///     foo: String,
/// }
///
/// impl MyTrait for MyStruct {
///     fn my_method(&self) {
///         println!("foo: {}", self.foo);
///     }
/// }
/// ```
pub trait Serialize: serialize::Sealed {}
impl<T: serde::ser::Serialize + ?Sized> Serialize for T {}

/// Any trait with this as a supertrait can be deserialized as a boxed trait object.
///
/// It is automatically implemented for all `T: serde::de::DeserializeOwned`, i.e. you should not implement it manually.
///
/// To use, simply add it as a supertrait to your trait:
/// ```
/// use serde_derive::{Serialize, Deserialize};
///
/// trait MyTrait: serde_traitobject::Serialize + serde_traitobject::Deserialize {
///     fn my_method(&self);
/// }
/// ```
///
/// Now your trait object is serializable!
/// ```
/// # use serde_derive::{Serialize, Deserialize};
/// #
/// # trait MyTrait: serde_traitobject::Serialize + serde_traitobject::Deserialize {
/// #     fn my_method(&self);
/// # }
/// #[derive(Serialize, Deserialize)]
/// struct Message(#[serde(with = "serde_traitobject")] Box<dyn MyTrait>);
///
/// // Woohoo, `Message` is now serializable!
/// ```
///
/// Any implementers of `MyTrait` would now have to themselves implement `serde::Serialize` and `serde::de::DeserializeOwned`. This would typically be through `serde_derive`, like:
/// ```
/// # use serde_derive::{Serialize, Deserialize};
/// # trait MyTrait: serde_traitobject::Serialize + serde_traitobject::Deserialize {
/// #     fn my_method(&self);
/// # }
/// # #[derive(Serialize, Deserialize)]
/// # struct Message(#[serde(with = "serde_traitobject")] Box<dyn MyTrait>);
/// #[derive(Serialize, Deserialize)]
/// struct MyStruct {
///     foo: String,
/// }
///
/// impl MyTrait for MyStruct {
///     fn my_method(&self) {
///         println!("foo: {}", self.foo);
///     }
/// }
/// ```
pub trait Deserialize: deserialize::Sealed {}
impl<T: serde::de::DeserializeOwned> Deserialize for T {}
impl Deserialize for str {}
impl<T: serde::de::DeserializeOwned> Deserialize for [T] {}

mod serialize {
	use metatype::type_id;

	pub trait Sealed: erased_serde::Serialize {
		fn serialize_sized<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
		where
			S: serde::Serializer,
			Self: Sized;

		#[inline]
		fn type_id(&self) -> u64
		where
			Self: 'static,
		{
			type_id::<Self>()
		}
	}

	impl<T: serde::ser::Serialize + ?Sized> Sealed for T {
		#[inline]
		default fn serialize_sized<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
		where
			S: serde::Serializer,
			Self: Sized,
		{
			let _ = serializer;
			unreachable!()
		}
	}

	impl<T: serde::ser::Serialize> Sealed for T {
		#[inline]
		fn serialize_sized<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
		where
			S: serde::Serializer,
			Self: Sized,
		{
			serde::ser::Serialize::serialize(self, serializer)
		}
	}
}

mod deserialize {
	use metatype::type_id;
	use std::ptr::NonNull;

	pub trait Sealed {
		fn deserialize_erased(
			self: *const Self, deserializer: &mut dyn erased_serde::Deserializer,
		) -> Result<NonNull<()>, erased_serde::Error> {
			let _ = deserializer;
			unreachable!()
		}

		fn deserialize_box<'de, D>(deserializer: D) -> Result<Box<Self>, D::Error>
		where
			D: serde::Deserializer<'de>,
			Self: Sized,
		{
			let _ = deserializer;
			unreachable!()
		}

		#[inline]
		fn type_id(self: *const Self) -> u64
		where
			Self: 'static,
		{
			type_id::<Self>()
		}
	}

	impl<T: serde::de::DeserializeOwned> Sealed for T {
		#[inline]
		fn deserialize_erased(
			self: *const Self, deserializer: &mut dyn erased_serde::Deserializer,
		) -> Result<NonNull<()>, erased_serde::Error> {
			erased_serde::deserialize::<Self>(deserializer)
				.map(|x| NonNull::new(Box::into_raw(Box::new(x)).cast()).unwrap())
		}

		#[inline]
		fn deserialize_box<'de, D>(deserializer: D) -> Result<Box<Self>, D::Error>
		where
			D: serde::Deserializer<'de>,
			Self: Sized,
		{
			serde::de::Deserialize::deserialize(deserializer).map(Box::new)
		}
	}

	impl Sealed for str {}
	impl<T: serde::de::DeserializeOwned> Sealed for [T] {}

	/// Rust currently doesn't support returning Self traitobjects from
	/// traitobject methods. Work around that by returning a thin pointer and
	/// fattening it.
	#[allow(clippy::module_name_repetitions)]
	#[inline]
	pub fn deserialize_erased<T: ?Sized>(
		self_: *const T, deserializer: &mut dyn erased_serde::Deserializer,
	) -> Result<Box<T>, erased_serde::Error>
	where
		T: Sealed,
	{
		self_.deserialize_erased(deserializer).map(|raw| {
			let object: *mut T = metatype::Type::fatten(raw.as_ptr(), metatype::Type::meta(self_));
			unsafe { Box::from_raw(object) }
		})
	}
}

/// Using a struct + trait to leverage specialisation to respectively handle
/// concrete, slices and traitobjects.
struct Serializer<T: Serialize + ?Sized + 'static>(marker::PhantomData<fn(T)>);
trait SerializerTrait<T: Serialize + ?Sized> {
	fn serialize<S>(t: &T, serializer: S) -> Result<S::Ok, S::Error>
	where
		S: serde::Serializer;
}
impl<T: Serialize> SerializerTrait<T> for Serializer<T> {
	#[inline]
	fn serialize<S>(t: &T, serializer: S) -> Result<S::Ok, S::Error>
	where
		S: serde::Serializer,
	{
		t.serialize_sized(serializer)
	}
}
impl SerializerTrait<str> for Serializer<str> {
	#[inline]
	fn serialize<S>(t: &str, serializer: S) -> Result<S::Ok, S::Error>
	where
		S: serde::Serializer,
	{
		serde::ser::Serialize::serialize(t, serializer)
	}
}
impl<T: serde::ser::Serialize> SerializerTrait<[T]> for Serializer<[T]> {
	#[inline]
	fn serialize<S>(t: &[T], serializer: S) -> Result<S::Ok, S::Error>
	where
		S: serde::Serializer,
	{
		serde::ser::Serialize::serialize(t, serializer)
	}
}
impl<T: Serialize + ?Sized + 'static> SerializerTrait<T> for Serializer<T> {
	#[inline]
	default fn serialize<S>(t: &T, serializer: S) -> Result<S::Ok, S::Error>
	where
		S: serde::Serializer,
	{
		let vtable = if let metatype::MetaType::TraitObject = metatype::Type::meta_type(t) {
			let trait_object: metatype::TraitObject = type_coerce(metatype::Type::meta(t));
			trait_object.vtable
		} else {
			panic!()
		};
		let mut tup = serializer.serialize_tuple(3)?;
		// We're making the assumption that the vtable is positioned the same
		// relative to the base vtable in every invocation, through e.g. being
		// in the same segment, or the binary being statically linked.
		//
		// See the [`relative`](https://github.com/alecmocatta/relative) crate
		// for more information.
		tup.serialize_element::<Vtable<T>>(&unsafe { Vtable::<T>::from(vtable) })?;
		tup.serialize_element::<u64>(&<T as serialize::Sealed>::type_id(t))?;
		tup.serialize_element::<SerializeErased<T>>(&SerializeErased(t))?;
		tup.end()
	}
}
struct SerializeErased<'a, T: Serialize + ?Sized + 'a>(&'a T);
impl<'a, T: Serialize + ?Sized> serde::ser::Serialize for SerializeErased<'a, T> {
	#[inline]
	fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
	where
		S: serde::Serializer,
	{
		erased_serde::serialize(self.0, serializer)
	}
}

/// Using a struct + trait to leverage specialisation to respectively handle
/// concrete, slices and traitobjects.
struct Deserializer<T: Deserialize + ?Sized + 'static>(marker::PhantomData<T>);
trait DeserializerTrait<T: Deserialize + ?Sized> {
	fn deserialize<'de, D>(deserializer: D) -> Result<boxed::Box<T>, D::Error>
	where
		D: serde::Deserializer<'de>;
}
impl<T: Deserialize> DeserializerTrait<T> for Deserializer<T> {
	#[inline]
	fn deserialize<'de, D>(deserializer: D) -> Result<boxed::Box<T>, D::Error>
	where
		D: serde::Deserializer<'de>,
	{
		<T as deserialize::Sealed>::deserialize_box(deserializer)
	}
}
impl DeserializerTrait<str> for Deserializer<str> {
	#[inline]
	fn deserialize<'de, D>(deserializer: D) -> Result<boxed::Box<str>, D::Error>
	where
		D: serde::Deserializer<'de>,
	{
		serde::de::Deserialize::deserialize(deserializer)
	}
}
impl<T: serde::de::DeserializeOwned> DeserializerTrait<[T]> for Deserializer<[T]> {
	#[inline]
	fn deserialize<'de, D>(deserializer: D) -> Result<boxed::Box<[T]>, D::Error>
	where
		D: serde::Deserializer<'de>,
	{
		serde::de::Deserialize::deserialize(deserializer)
	}
}
impl<T: Deserialize + ?Sized + 'static> DeserializerTrait<T> for Deserializer<T> {
	#[inline]
	default fn deserialize<'de, D>(deserializer: D) -> Result<boxed::Box<T>, D::Error>
	where
		D: serde::Deserializer<'de>,
	{
		struct Visitor<T: Deserialize + ?Sized>(marker::PhantomData<T>);
		impl<'de, T: Deserialize + ?Sized + 'static> serde::de::Visitor<'de> for Visitor<T> {
			type Value = boxed::Box<T>;
			fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
				write!(formatter, "a \"{}\" trait object", type_name::<T>())
			}
			#[inline]
			fn visit_seq<A>(self, mut seq: A) -> Result<boxed::Box<T>, A::Error>
			where
				A: serde::de::SeqAccess<'de>,
			{
				let t0: Vtable<T> = match seq.next_element()? {
					Some(value) => value,
					None => return Err(serde::de::Error::invalid_length(0, &self)),
				};
				let t1: u64 = match seq.next_element()? {
					Some(value) => value,
					None => return Err(serde::de::Error::invalid_length(1, &self)),
				};
				let meta = metatype::TraitObject { vtable: t0.to() };
				let object: *const T = metatype::Type::dangling(type_coerce(meta)).as_ptr();
				assert_eq!(t1, object.type_id(), "Deserializing the trait object \"{}\" failed in a way that should never happen. Please file an issue! https://github.com/alecmocatta/serde_traitobject/issues/new", type_name::<T>());
				let t2: boxed::Box<T> = match seq.next_element_seed(DeserializeErased(object))? {
					Some(value) => value,
					None => return Err(serde::de::Error::invalid_length(2, &self)),
				};
				Ok(t2)
			}
		}
		deserializer.deserialize_tuple(3, Visitor(marker::PhantomData))
	}
}
struct DeserializeErased<T: Deserialize + ?Sized>(*const T);
impl<'de, T: Deserialize + ?Sized> serde::de::DeserializeSeed<'de> for DeserializeErased<T> {
	type Value = boxed::Box<T>;

	#[inline]
	fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
	where
		D: serde::de::Deserializer<'de>,
	{
		let deserializer = &mut <dyn erased_serde::Deserializer>::erase(deserializer);
		deserialize::deserialize_erased(self.0, deserializer).map_err(serde::de::Error::custom)
	}
}

/// Serialize a value by reference.
///
/// This is intended to enable:
/// ```
/// # use serde_derive::{Serialize, Deserialize};
///
/// #[derive(Serialize, Deserialize)]
/// struct MyStruct {
///     #[serde(with = "serde_traitobject")]
///     field: Box<dyn serde_traitobject::Any>,
/// }
/// ```
///
/// Or, alternatively, if only Serialize is desired:
/// ```
/// # use serde_derive::{Serialize, Deserialize};
///
/// #[derive(Serialize)]
/// struct MyStruct {
///     #[serde(serialize_with = "serde_traitobject::serialize")]
///     field: Box<dyn serde_traitobject::Any>,
/// }
/// ```
pub fn serialize<T: Serialize + ?Sized + 'static, B: AsRef<T> + ?Sized, S>(
	t: &B, serializer: S,
) -> Result<S::Ok, S::Error>
where
	S: serde::Serializer,
{
	Serializer::<T>::serialize(t.as_ref(), serializer)
}

/// Deserialize a value `T` into `B` where `Box<T>: Into<B>`.
///
/// This is intended to enable:
/// ```
/// # use serde_derive::{Serialize, Deserialize};
///
/// #[derive(Serialize, Deserialize)]
/// struct MyStruct {
///     #[serde(with = "serde_traitobject")]
///     field: Box<dyn serde_traitobject::Any>,
/// }
/// ```
///
/// Or, alternatively, if only Deserialize is desired:
/// ```
/// # use serde_derive::{Serialize, Deserialize};
///
/// #[derive(Deserialize)]
/// struct MyStruct {
///     #[serde(deserialize_with = "serde_traitobject::deserialize")]
///     field: Box<dyn serde_traitobject::Any>,
/// }
/// ```
pub fn deserialize<'de, T: Deserialize + ?Sized + 'static, B, D>(
	deserializer: D,
) -> Result<B, D::Error>
where
	D: serde::Deserializer<'de>,
	boxed::Box<T>: Into<B>,
{
	Deserializer::<T>::deserialize(deserializer).map(<boxed::Box<T> as Into<B>>::into)
}