Mixing
How do I deserialize into trait, not a concrete type?
I'm trying to do struct serialization, in which the bytes would eventually be sent down a pipe, reconstructed and methods be called on them.
I created a trait these structs would implement as appropriate and I'm using serde and serde-cbor for serialization:
extern crate serde_cbor;
#[macro_use]
extern crate serde_derive;
extern crate serde;
use serde_cbor::ser::*;
use serde_cbor::de::*;
trait Contract {
fn do_something(&self);
}
#[derive(Debug, Serialize, Deserialize)]
struct Foo {
x: u32,
y: u32,
}
#[derive(Debug, Serialize, Deserialize)]
struct Bar {
data: Vec<Foo>,
}
#[derive(Debug, Serialize, Deserialize)]
struct Baz {
data: Vec<Foo>,
tag: String,
}
impl Contract for Bar {
fn do_something(&self) {
println!("I'm a Bar and this is my data {:?}", self.data);
}
}
impl Contract for Baz {
fn do_something(&self) {
println!("I'm Baz {} and this is my data {:?}", self.tag, self.data);
}
}
fn main() {
let data = Bar { data: vec![Foo { x: 1, y: 2 }, Foo { x: 3, y: 4 }, Foo { x: 7, y: 8 }] };
data.do_something();
let value = to_vec(&data).unwrap();
let res: Result<Contract, _> = from_reader(&value[..]);
let res = res.unwrap();
println!("{:?}", res);
res.do_something();
}
When I try to reconstruct the bytes using the trait as the type (given that I wouldn't know which underlying object is being sent), the compiler complains that the trait does not implement the Sized trait:
error[E0277]: the trait bound `Contract: std::marker::Sized` is not satisfied
--> src/main.rs:52:15
|
52 | let res: Result<Contract, _> = from_reader(&value[..]);
| ^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Sized` is not implemented for `Contract`
|
= note: `Contract` does not have a constant size known at compile-time
= note: required by `std::result::Result`
I guess it makes sense since the compiler doesn't know how big the struct is supposed to be and doesn't know how to line up the bytes for it. If I change the line where I deserialize the object to specify the actual struct type, it works:
let res: Result<Bar, _> = from_reader(&value[..]);
Is there a better pattern to achieve this serialization + polymorphism behavior?
serialization rust serde cbor
edited Feb 22 '17 at 15:55
Shepmaster
157k14318460
asked Feb 22 '17 at 13:32
Dash83Dash83
331315
|
show 1 more comment
I'm trying to do struct serialization, in which the bytes would eventually be sent down a pipe, reconstructed and methods be called on them.
I created a trait these structs would implement as appropriate and I'm using serde and serde-cbor for serialization:
extern crate serde_cbor;
#[macro_use]
extern crate serde_derive;
extern crate serde;
use serde_cbor::ser::*;
use serde_cbor::de::*;
trait Contract {
fn do_something(&self);
}
#[derive(Debug, Serialize, Deserialize)]
struct Foo {
x: u32,
y: u32,
}
#[derive(Debug, Serialize, Deserialize)]
struct Bar {
data: Vec<Foo>,
}
#[derive(Debug, Serialize, Deserialize)]
struct Baz {
data: Vec<Foo>,
tag: String,
}
impl Contract for Bar {
fn do_something(&self) {
println!("I'm a Bar and this is my data {:?}", self.data);
}
}
impl Contract for Baz {
fn do_something(&self) {
println!("I'm Baz {} and this is my data {:?}", self.tag, self.data);
}
}
fn main() {
let data = Bar { data: vec![Foo { x: 1, y: 2 }, Foo { x: 3, y: 4 }, Foo { x: 7, y: 8 }] };
data.do_something();
let value = to_vec(&data).unwrap();
let res: Result<Contract, _> = from_reader(&value[..]);
let res = res.unwrap();
println!("{:?}", res);
res.do_something();
}
When I try to reconstruct the bytes using the trait as the type (given that I wouldn't know which underlying object is being sent), the compiler complains that the trait does not implement the Sized trait:
error[E0277]: the trait bound `Contract: std::marker::Sized` is not satisfied
--> src/main.rs:52:15
|
52 | let res: Result<Contract, _> = from_reader(&value[..]);
| ^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Sized` is not implemented for `Contract`
|
= note: `Contract` does not have a constant size known at compile-time
= note: required by `std::result::Result`
I guess it makes sense since the compiler doesn't know how big the struct is supposed to be and doesn't know how to line up the bytes for it. If I change the line where I deserialize the object to specify the actual struct type, it works:
let res: Result<Bar, _> = from_reader(&value[..]);
Is there a better pattern to achieve this serialization + polymorphism behavior?
serialization rust serde cbor
edited Feb 22 '17 at 15:55
Shepmaster
157k14318460
asked Feb 22 '17 at 13:32
Dash83Dash83
331315
2
I... don't think you can do that. You can't recover the struct unless you know its concrete type, and you can't call methods on it unless you have a pointer to its vtable -- which you can't figure out unless you have access to its concrete type. Can you serialize a vtable?
– trentcl
Feb 22 '17 at 14:00
Seems to be the case, but I was hoping someone would point out something I'm missing. I have a non-idiomatic solution for this but adds coupling to the code... so I'm looking for something better.
– Dash83
Feb 22 '17 at 14:09
3
Are you sure you want polymorphism and not simply an enum? Do you need your code to work with user supplied types?
– oli_obk
Feb 22 '17 at 16:12
I.... you know... but....no. You are correct, @ker. The "non-idiomatic" solution I had becomes far more natural when using enums with data associated to them. I keep trying to use enums as standard C enums, but I can change my design to use enums. If you post your suggestions as an answer, I'll accept it.
– Dash83
Feb 22 '17 at 17:42
1
What about deserializing into an implementation that also implementsIntofor all otherContractimplementations?
– w.brian
Feb 22 '17 at 21:45
|
show 1 more comment
I'm trying to do struct serialization, in which the bytes would eventually be sent down a pipe, reconstructed and methods be called on them.
I created a trait these structs would implement as appropriate and I'm using serde and serde-cbor for serialization:
extern crate serde_cbor;
#[macro_use]
extern crate serde_derive;
extern crate serde;
use serde_cbor::ser::*;
use serde_cbor::de::*;
trait Contract {
fn do_something(&self);
}
#[derive(Debug, Serialize, Deserialize)]
struct Foo {
x: u32,
y: u32,
}
#[derive(Debug, Serialize, Deserialize)]
struct Bar {
data: Vec<Foo>,
}
#[derive(Debug, Serialize, Deserialize)]
struct Baz {
data: Vec<Foo>,
tag: String,
}
impl Contract for Bar {
fn do_something(&self) {
println!("I'm a Bar and this is my data {:?}", self.data);
}
}
impl Contract for Baz {
fn do_something(&self) {
println!("I'm Baz {} and this is my data {:?}", self.tag, self.data);
}
}
fn main() {
let data = Bar { data: vec![Foo { x: 1, y: 2 }, Foo { x: 3, y: 4 }, Foo { x: 7, y: 8 }] };
data.do_something();
let value = to_vec(&data).unwrap();
let res: Result<Contract, _> = from_reader(&value[..]);
let res = res.unwrap();
println!("{:?}", res);
res.do_something();
}
When I try to reconstruct the bytes using the trait as the type (given that I wouldn't know which underlying object is being sent), the compiler complains that the trait does not implement the Sized trait:
error[E0277]: the trait bound `Contract: std::marker::Sized` is not satisfied
--> src/main.rs:52:15
|
52 | let res: Result<Contract, _> = from_reader(&value[..]);
| ^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Sized` is not implemented for `Contract`
|
= note: `Contract` does not have a constant size known at compile-time
= note: required by `std::result::Result`
I guess it makes sense since the compiler doesn't know how big the struct is supposed to be and doesn't know how to line up the bytes for it. If I change the line where I deserialize the object to specify the actual struct type, it works:
let res: Result<Bar, _> = from_reader(&value[..]);
Is there a better pattern to achieve this serialization + polymorphism behavior?
serialization rust serde cbor
edited Feb 22 '17 at 15:55
Shepmaster
157k14318460
asked Feb 22 '17 at 13:32
Dash83Dash83
331315
I'm trying to do struct serialization, in which the bytes would eventually be sent down a pipe, reconstructed and methods be called on them.
I created a trait these structs would implement as appropriate and I'm using serde and serde-cbor for serialization:
extern crate serde_cbor;
#[macro_use]
extern crate serde_derive;
extern crate serde;
use serde_cbor::ser::*;
use serde_cbor::de::*;
trait Contract {
fn do_something(&self);
}
#[derive(Debug, Serialize, Deserialize)]
struct Foo {
x: u32,
y: u32,
}
#[derive(Debug, Serialize, Deserialize)]
struct Bar {
data: Vec<Foo>,
}
#[derive(Debug, Serialize, Deserialize)]
struct Baz {
data: Vec<Foo>,
tag: String,
}
impl Contract for Bar {
fn do_something(&self) {
println!("I'm a Bar and this is my data {:?}", self.data);
}
}
impl Contract for Baz {
fn do_something(&self) {
println!("I'm Baz {} and this is my data {:?}", self.tag, self.data);
}
}
fn main() {
let data = Bar { data: vec![Foo { x: 1, y: 2 }, Foo { x: 3, y: 4 }, Foo { x: 7, y: 8 }] };
data.do_something();
let value = to_vec(&data).unwrap();
let res: Result<Contract, _> = from_reader(&value[..]);
let res = res.unwrap();
println!("{:?}", res);
res.do_something();
}
When I try to reconstruct the bytes using the trait as the type (given that I wouldn't know which underlying object is being sent), the compiler complains that the trait does not implement the Sized trait:
error[E0277]: the trait bound `Contract: std::marker::Sized` is not satisfied
--> src/main.rs:52:15
|
52 | let res: Result<Contract, _> = from_reader(&value[..]);
| ^^^^^^^^^^^^^^^^^^^ the trait `std::marker::Sized` is not implemented for `Contract`
|
= note: `Contract` does not have a constant size known at compile-time
= note: required by `std::result::Result`
I guess it makes sense since the compiler doesn't know how big the struct is supposed to be and doesn't know how to line up the bytes for it. If I change the line where I deserialize the object to specify the actual struct type, it works:
let res: Result<Bar, _> = from_reader(&value[..]);
Is there a better pattern to achieve this serialization + polymorphism behavior?
serialization rust serde cbor
serialization rust serde cbor
edited Feb 22 '17 at 15:55
Shepmaster
157k14318460
asked Feb 22 '17 at 13:32
Dash83Dash83
331315
edited Feb 22 '17 at 15:55
Shepmaster
157k14318460
asked Feb 22 '17 at 13:32
Dash83Dash83
331315
edited Feb 22 '17 at 15:55
Shepmaster
157k14318460
edited Feb 22 '17 at 15:55
Shepmaster
157k14318460
edited Feb 22 '17 at 15:55
Shepmaster
157k14318460
157k14318460
asked Feb 22 '17 at 13:32
Dash83Dash83
331315
asked Feb 22 '17 at 13:32
Dash83Dash83
331315
asked Feb 22 '17 at 13:32
Dash83Dash83
331315
331315
2
I... don't think you can do that. You can't recover the struct unless you know its concrete type, and you can't call methods on it unless you have a pointer to its vtable -- which you can't figure out unless you have access to its concrete type. Can you serialize a vtable?
– trentcl
Feb 22 '17 at 14:00
Seems to be the case, but I was hoping someone would point out something I'm missing. I have a non-idiomatic solution for this but adds coupling to the code... so I'm looking for something better.
– Dash83
Feb 22 '17 at 14:09
3
Are you sure you want polymorphism and not simply an enum? Do you need your code to work with user supplied types?
– oli_obk
Feb 22 '17 at 16:12
I.... you know... but....no. You are correct, @ker. The "non-idiomatic" solution I had becomes far more natural when using enums with data associated to them. I keep trying to use enums as standard C enums, but I can change my design to use enums. If you post your suggestions as an answer, I'll accept it.
– Dash83
Feb 22 '17 at 17:42
1
What about deserializing into an implementation that also implementsIntofor all otherContractimplementations?
– w.brian
Feb 22 '17 at 21:45
|
show 1 more comment
2
I... don't think you can do that. You can't recover the struct unless you know its concrete type, and you can't call methods on it unless you have a pointer to its vtable -- which you can't figure out unless you have access to its concrete type. Can you serialize a vtable?
– trentcl
Feb 22 '17 at 14:00
Seems to be the case, but I was hoping someone would point out something I'm missing. I have a non-idiomatic solution for this but adds coupling to the code... so I'm looking for something better.
– Dash83
Feb 22 '17 at 14:09
3
Are you sure you want polymorphism and not simply an enum? Do you need your code to work with user supplied types?
– oli_obk
Feb 22 '17 at 16:12
I.... you know... but....no. You are correct, @ker. The "non-idiomatic" solution I had becomes far more natural when using enums with data associated to them. I keep trying to use enums as standard C enums, but I can change my design to use enums. If you post your suggestions as an answer, I'll accept it.
– Dash83
Feb 22 '17 at 17:42
1
What about deserializing into an implementation that also implementsIntofor all otherContractimplementations?
– w.brian
Feb 22 '17 at 21:45
2
2
I... don't think you can do that. You can't recover the struct unless you know its concrete type, and you can't call methods on it unless you have a pointer to its vtable -- which you can't figure out unless you have access to its concrete type. Can you serialize a vtable?
– trentcl
Feb 22 '17 at 14:00
I... don't think you can do that. You can't recover the struct unless you know its concrete type, and you can't call methods on it unless you have a pointer to its vtable -- which you can't figure out unless you have access to its concrete type. Can you serialize a vtable?
– trentcl
Feb 22 '17 at 14:00
Seems to be the case, but I was hoping someone would point out something I'm missing. I have a non-idiomatic solution for this but adds coupling to the code... so I'm looking for something better.
– Dash83
Feb 22 '17 at 14:09
Seems to be the case, but I was hoping someone would point out something I'm missing. I have a non-idiomatic solution for this but adds coupling to the code... so I'm looking for something better.
– Dash83
Feb 22 '17 at 14:09
3
3
Are you sure you want polymorphism and not simply an enum? Do you need your code to work with user supplied types?
– oli_obk
Feb 22 '17 at 16:12
Are you sure you want polymorphism and not simply an enum? Do you need your code to work with user supplied types?
– oli_obk
Feb 22 '17 at 16:12
I.... you know... but....no. You are correct, @ker. The "non-idiomatic" solution I had becomes far more natural when using enums with data associated to them. I keep trying to use enums as standard C enums, but I can change my design to use enums. If you post your suggestions as an answer, I'll accept it.
– Dash83
Feb 22 '17 at 17:42
I.... you know... but....no. You are correct, @ker. The "non-idiomatic" solution I had becomes far more natural when using enums with data associated to them. I keep trying to use enums as standard C enums, but I can change my design to use enums. If you post your suggestions as an answer, I'll accept it.
– Dash83
Feb 22 '17 at 17:42
1
1
What about deserializing into an implementation that also implements
Into for all other Contract implementations?– w.brian
Feb 22 '17 at 21:45
What about deserializing into an implementation that also implements
Into for all other Contract implementations?– w.brian
Feb 22 '17 at 21:45
|
show 1 more comment
2 Answers
2
active
oldest
votes
It looks like you fell into the same trap that I fell into when I moved from C++ to Rust. Trying to use polymorphism to model a fixed set of variants of a type. Rust's enums (similar to Haskell's enums, and equivalent to Ada's variant record types) are different from classical enums in other languages, because the enum variants can have fields of their own.
I suggest you change your code to
#[derive(Debug, Serialize, Deserialize)]
enum Contract {
Bar { data: Vec<Foo> },
Baz { data: Vec<Foo>, tag: String },
}
#[derive(Debug, Serialize, Deserialize)]
struct Foo {
x: u32,
y: u32,
}
impl Contract {
fn do_something(&self) {
match *self {
Contract::Bar { ref data } => println!("I'm a Bar and this is my data {:?}", data),
Contract::Baz { ref data, ref tag } => {
println!("I'm Baz {} and this is my data {:?}", tag, data)
}
}
}
}
answered Feb 24 '17 at 9:06
oli_obkoli_obk
16.7k14567
Used the structures Bar and Baz as the associated data for the enum, but went pretty much with this design otherwise. Thanks!
– Dash83
Feb 24 '17 at 12:31
What about if there is arbitrary set of type from a trait with type parameters?
– Shisoft
Nov 2 '17 at 14:16
@Shisoft not sure I understand. Why don't you open a new question?
– oli_obk
Nov 3 '17 at 15:08
add a comment |
Adding on to oli_obk's answer, you can use Serde's enum representation to distinguish between the types.
Here, I use the internally-tagged representation to deserialize these two similar objects into the appropriate variant:
{
"driver": "file",
"path": "/var/log/foo"
}
{
"driver": "http",
"port": 8080,
"endpoint": "/api/bar"
}
use serde; // 1.0.82
use serde_derive::*; // 1.0.82
use serde_json; // 1.0.33
#[derive(Debug, Deserialize, PartialEq)]
#[serde(tag = "driver")]
enum Driver {
#[serde(rename = "file")]
File { path: String },
#[serde(rename = "http")]
Http { port: u16, endpoint: String }
}
fn main() {
let f = r#"
{
"driver": "file",
"path": "/var/log/foo"
}
"#;
let h = r#"
{
"driver": "http",
"port": 8080,
"endpoint": "/api/bar"
}
"#;
let f: Driver = serde_json::from_str(f).unwrap();
assert_eq!(f, Driver::File { path: "/var/log/foo".into() });
let h: Driver = serde_json::from_str(h).unwrap();
assert_eq!(h, Driver::Http { port: 8080, endpoint: "/api/bar".into() });
}
You don't have to squash it all into one enum, you can create separate types as well:
#[derive(Debug, Deserialize, PartialEq)]
#[serde(tag = "driver")]
enum Driver {
#[serde(rename = "file")]
File(File),
#[serde(rename = "http")]
Http(Http),
}
#[derive(Debug, Deserialize, PartialEq)]
struct File {
path: String,
}
#[derive(Debug, Deserialize, PartialEq)]
struct Http {
port: u16,
endpoint: String,
}
answered Jan 1 at 17:19
ShepmasterShepmaster
157k14318460
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
It looks like you fell into the same trap that I fell into when I moved from C++ to Rust. Trying to use polymorphism to model a fixed set of variants of a type. Rust's enums (similar to Haskell's enums, and equivalent to Ada's variant record types) are different from classical enums in other languages, because the enum variants can have fields of their own.
I suggest you change your code to
#[derive(Debug, Serialize, Deserialize)]
enum Contract {
Bar { data: Vec<Foo> },
Baz { data: Vec<Foo>, tag: String },
}
#[derive(Debug, Serialize, Deserialize)]
struct Foo {
x: u32,
y: u32,
}
impl Contract {
fn do_something(&self) {
match *self {
Contract::Bar { ref data } => println!("I'm a Bar and this is my data {:?}", data),
Contract::Baz { ref data, ref tag } => {
println!("I'm Baz {} and this is my data {:?}", tag, data)
}
}
}
}
answered Feb 24 '17 at 9:06
oli_obkoli_obk
16.7k14567
Used the structures Bar and Baz as the associated data for the enum, but went pretty much with this design otherwise. Thanks!
– Dash83
Feb 24 '17 at 12:31
What about if there is arbitrary set of type from a trait with type parameters?
– Shisoft
Nov 2 '17 at 14:16
@Shisoft not sure I understand. Why don't you open a new question?
– oli_obk
Nov 3 '17 at 15:08
add a comment |
It looks like you fell into the same trap that I fell into when I moved from C++ to Rust. Trying to use polymorphism to model a fixed set of variants of a type. Rust's enums (similar to Haskell's enums, and equivalent to Ada's variant record types) are different from classical enums in other languages, because the enum variants can have fields of their own.
I suggest you change your code to
#[derive(Debug, Serialize, Deserialize)]
enum Contract {
Bar { data: Vec<Foo> },
Baz { data: Vec<Foo>, tag: String },
}
#[derive(Debug, Serialize, Deserialize)]
struct Foo {
x: u32,
y: u32,
}
impl Contract {
fn do_something(&self) {
match *self {
Contract::Bar { ref data } => println!("I'm a Bar and this is my data {:?}", data),
Contract::Baz { ref data, ref tag } => {
println!("I'm Baz {} and this is my data {:?}", tag, data)
}
}
}
}
answered Feb 24 '17 at 9:06
oli_obkoli_obk
16.7k14567
Used the structures Bar and Baz as the associated data for the enum, but went pretty much with this design otherwise. Thanks!
– Dash83
Feb 24 '17 at 12:31
What about if there is arbitrary set of type from a trait with type parameters?
– Shisoft
Nov 2 '17 at 14:16
@Shisoft not sure I understand. Why don't you open a new question?
– oli_obk
Nov 3 '17 at 15:08
add a comment |
It looks like you fell into the same trap that I fell into when I moved from C++ to Rust. Trying to use polymorphism to model a fixed set of variants of a type. Rust's enums (similar to Haskell's enums, and equivalent to Ada's variant record types) are different from classical enums in other languages, because the enum variants can have fields of their own.
I suggest you change your code to
#[derive(Debug, Serialize, Deserialize)]
enum Contract {
Bar { data: Vec<Foo> },
Baz { data: Vec<Foo>, tag: String },
}
#[derive(Debug, Serialize, Deserialize)]
struct Foo {
x: u32,
y: u32,
}
impl Contract {
fn do_something(&self) {
match *self {
Contract::Bar { ref data } => println!("I'm a Bar and this is my data {:?}", data),
Contract::Baz { ref data, ref tag } => {
println!("I'm Baz {} and this is my data {:?}", tag, data)
}
}
}
}
answered Feb 24 '17 at 9:06
oli_obkoli_obk
16.7k14567
It looks like you fell into the same trap that I fell into when I moved from C++ to Rust. Trying to use polymorphism to model a fixed set of variants of a type. Rust's enums (similar to Haskell's enums, and equivalent to Ada's variant record types) are different from classical enums in other languages, because the enum variants can have fields of their own.
I suggest you change your code to
#[derive(Debug, Serialize, Deserialize)]
enum Contract {
Bar { data: Vec<Foo> },
Baz { data: Vec<Foo>, tag: String },
}
#[derive(Debug, Serialize, Deserialize)]
struct Foo {
x: u32,
y: u32,
}
impl Contract {
fn do_something(&self) {
match *self {
Contract::Bar { ref data } => println!("I'm a Bar and this is my data {:?}", data),
Contract::Baz { ref data, ref tag } => {
println!("I'm Baz {} and this is my data {:?}", tag, data)
}
}
}
}
answered Feb 24 '17 at 9:06
oli_obkoli_obk
16.7k14567
edited Feb 24 '17 at 11:47
answered Feb 24 '17 at 9:06
oli_obkoli_obk
16.7k14567
answered Feb 24 '17 at 9:06
oli_obkoli_obk
16.7k14567
answered Feb 24 '17 at 9:06
oli_obkoli_obk
16.7k14567
16.7k14567
Used the structures Bar and Baz as the associated data for the enum, but went pretty much with this design otherwise. Thanks!
– Dash83
Feb 24 '17 at 12:31
What about if there is arbitrary set of type from a trait with type parameters?
– Shisoft
Nov 2 '17 at 14:16
@Shisoft not sure I understand. Why don't you open a new question?
– oli_obk
Nov 3 '17 at 15:08
add a comment |
Used the structures Bar and Baz as the associated data for the enum, but went pretty much with this design otherwise. Thanks!
– Dash83
Feb 24 '17 at 12:31
What about if there is arbitrary set of type from a trait with type parameters?
– Shisoft
Nov 2 '17 at 14:16
@Shisoft not sure I understand. Why don't you open a new question?
– oli_obk
Nov 3 '17 at 15:08
Used the structures Bar and Baz as the associated data for the enum, but went pretty much with this design otherwise. Thanks!
– Dash83
Feb 24 '17 at 12:31
Used the structures Bar and Baz as the associated data for the enum, but went pretty much with this design otherwise. Thanks!
– Dash83
Feb 24 '17 at 12:31
What about if there is arbitrary set of type from a trait with type parameters?
– Shisoft
Nov 2 '17 at 14:16
What about if there is arbitrary set of type from a trait with type parameters?
– Shisoft
Nov 2 '17 at 14:16
@Shisoft not sure I understand. Why don't you open a new question?
– oli_obk
Nov 3 '17 at 15:08
@Shisoft not sure I understand. Why don't you open a new question?
– oli_obk
Nov 3 '17 at 15:08
add a comment |
Adding on to oli_obk's answer, you can use Serde's enum representation to distinguish between the types.
Here, I use the internally-tagged representation to deserialize these two similar objects into the appropriate variant:
{
"driver": "file",
"path": "/var/log/foo"
}
{
"driver": "http",
"port": 8080,
"endpoint": "/api/bar"
}
use serde; // 1.0.82
use serde_derive::*; // 1.0.82
use serde_json; // 1.0.33
#[derive(Debug, Deserialize, PartialEq)]
#[serde(tag = "driver")]
enum Driver {
#[serde(rename = "file")]
File { path: String },
#[serde(rename = "http")]
Http { port: u16, endpoint: String }
}
fn main() {
let f = r#"
{
"driver": "file",
"path": "/var/log/foo"
}
"#;
let h = r#"
{
"driver": "http",
"port": 8080,
"endpoint": "/api/bar"
}
"#;
let f: Driver = serde_json::from_str(f).unwrap();
assert_eq!(f, Driver::File { path: "/var/log/foo".into() });
let h: Driver = serde_json::from_str(h).unwrap();
assert_eq!(h, Driver::Http { port: 8080, endpoint: "/api/bar".into() });
}
You don't have to squash it all into one enum, you can create separate types as well:
#[derive(Debug, Deserialize, PartialEq)]
#[serde(tag = "driver")]
enum Driver {
#[serde(rename = "file")]
File(File),
#[serde(rename = "http")]
Http(Http),
}
#[derive(Debug, Deserialize, PartialEq)]
struct File {
path: String,
}
#[derive(Debug, Deserialize, PartialEq)]
struct Http {
port: u16,
endpoint: String,
}
answered Jan 1 at 17:19
ShepmasterShepmaster
157k14318460
add a comment |
Adding on to oli_obk's answer, you can use Serde's enum representation to distinguish between the types.
Here, I use the internally-tagged representation to deserialize these two similar objects into the appropriate variant:
{
"driver": "file",
"path": "/var/log/foo"
}
{
"driver": "http",
"port": 8080,
"endpoint": "/api/bar"
}
use serde; // 1.0.82
use serde_derive::*; // 1.0.82
use serde_json; // 1.0.33
#[derive(Debug, Deserialize, PartialEq)]
#[serde(tag = "driver")]
enum Driver {
#[serde(rename = "file")]
File { path: String },
#[serde(rename = "http")]
Http { port: u16, endpoint: String }
}
fn main() {
let f = r#"
{
"driver": "file",
"path": "/var/log/foo"
}
"#;
let h = r#"
{
"driver": "http",
"port": 8080,
"endpoint": "/api/bar"
}
"#;
let f: Driver = serde_json::from_str(f).unwrap();
assert_eq!(f, Driver::File { path: "/var/log/foo".into() });
let h: Driver = serde_json::from_str(h).unwrap();
assert_eq!(h, Driver::Http { port: 8080, endpoint: "/api/bar".into() });
}
You don't have to squash it all into one enum, you can create separate types as well:
#[derive(Debug, Deserialize, PartialEq)]
#[serde(tag = "driver")]
enum Driver {
#[serde(rename = "file")]
File(File),
#[serde(rename = "http")]
Http(Http),
}
#[derive(Debug, Deserialize, PartialEq)]
struct File {
path: String,
}
#[derive(Debug, Deserialize, PartialEq)]
struct Http {
port: u16,
endpoint: String,
}
answered Jan 1 at 17:19
ShepmasterShepmaster
157k14318460
add a comment |
Adding on to oli_obk's answer, you can use Serde's enum representation to distinguish between the types.
Here, I use the internally-tagged representation to deserialize these two similar objects into the appropriate variant:
{
"driver": "file",
"path": "/var/log/foo"
}
{
"driver": "http",
"port": 8080,
"endpoint": "/api/bar"
}
use serde; // 1.0.82
use serde_derive::*; // 1.0.82
use serde_json; // 1.0.33
#[derive(Debug, Deserialize, PartialEq)]
#[serde(tag = "driver")]
enum Driver {
#[serde(rename = "file")]
File { path: String },
#[serde(rename = "http")]
Http { port: u16, endpoint: String }
}
fn main() {
let f = r#"
{
"driver": "file",
"path": "/var/log/foo"
}
"#;
let h = r#"
{
"driver": "http",
"port": 8080,
"endpoint": "/api/bar"
}
"#;
let f: Driver = serde_json::from_str(f).unwrap();
assert_eq!(f, Driver::File { path: "/var/log/foo".into() });
let h: Driver = serde_json::from_str(h).unwrap();
assert_eq!(h, Driver::Http { port: 8080, endpoint: "/api/bar".into() });
}
You don't have to squash it all into one enum, you can create separate types as well:
#[derive(Debug, Deserialize, PartialEq)]
#[serde(tag = "driver")]
enum Driver {
#[serde(rename = "file")]
File(File),
#[serde(rename = "http")]
Http(Http),
}
#[derive(Debug, Deserialize, PartialEq)]
struct File {
path: String,
}
#[derive(Debug, Deserialize, PartialEq)]
struct Http {
port: u16,
endpoint: String,
}
answered Jan 1 at 17:19
ShepmasterShepmaster
157k14318460
Adding on to oli_obk's answer, you can use Serde's enum representation to distinguish between the types.
Here, I use the internally-tagged representation to deserialize these two similar objects into the appropriate variant:
{
"driver": "file",
"path": "/var/log/foo"
}
{
"driver": "http",
"port": 8080,
"endpoint": "/api/bar"
}
use serde; // 1.0.82
use serde_derive::*; // 1.0.82
use serde_json; // 1.0.33
#[derive(Debug, Deserialize, PartialEq)]
#[serde(tag = "driver")]
enum Driver {
#[serde(rename = "file")]
File { path: String },
#[serde(rename = "http")]
Http { port: u16, endpoint: String }
}
fn main() {
let f = r#"
{
"driver": "file",
"path": "/var/log/foo"
}
"#;
let h = r#"
{
"driver": "http",
"port": 8080,
"endpoint": "/api/bar"
}
"#;
let f: Driver = serde_json::from_str(f).unwrap();
assert_eq!(f, Driver::File { path: "/var/log/foo".into() });
let h: Driver = serde_json::from_str(h).unwrap();
assert_eq!(h, Driver::Http { port: 8080, endpoint: "/api/bar".into() });
}
You don't have to squash it all into one enum, you can create separate types as well:
#[derive(Debug, Deserialize, PartialEq)]
#[serde(tag = "driver")]
enum Driver {
#[serde(rename = "file")]
File(File),
#[serde(rename = "http")]
Http(Http),
}
#[derive(Debug, Deserialize, PartialEq)]
struct File {
path: String,
}
#[derive(Debug, Deserialize, PartialEq)]
struct Http {
port: u16,
endpoint: String,
}
answered Jan 1 at 17:19
ShepmasterShepmaster
157k14318460
edited Jan 1 at 17:29
answered Jan 1 at 17:19
ShepmasterShepmaster
157k14318460
answered Jan 1 at 17:19
ShepmasterShepmaster
157k14318460
answered Jan 1 at 17:19
ShepmasterShepmaster
157k14318460
157k14318460
add a comment |
add a comment |
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2
I... don't think you can do that. You can't recover the struct unless you know its concrete type, and you can't call methods on it unless you have a pointer to its vtable -- which you can't figure out unless you have access to its concrete type. Can you serialize a vtable?
– trentcl
Feb 22 '17 at 14:00
Seems to be the case, but I was hoping someone would point out something I'm missing. I have a non-idiomatic solution for this but adds coupling to the code... so I'm looking for something better.
– Dash83
Feb 22 '17 at 14:09
3
Are you sure you want polymorphism and not simply an enum? Do you need your code to work with user supplied types?
– oli_obk
Feb 22 '17 at 16:12
I.... you know... but....no. You are correct, @ker. The "non-idiomatic" solution I had becomes far more natural when using enums with data associated to them. I keep trying to use enums as standard C enums, but I can change my design to use enums. If you post your suggestions as an answer, I'll accept it.
– Dash83
Feb 22 '17 at 17:42
1
What about deserializing into an implementation that also implements
Intofor all otherContractimplementations?– w.brian
Feb 22 '17 at 21:45