File: try_from.md

package info (click to toggle)
firefox 149.0-1
  • links: PTS, VCS
  • area: main
  • in suites: sid
  • size: 4,767,760 kB
  • sloc: cpp: 7,416,064; javascript: 6,752,859; ansic: 3,774,850; python: 1,250,473; xml: 641,578; asm: 439,191; java: 186,617; sh: 56,634; makefile: 18,856; objc: 13,092; perl: 12,763; pascal: 5,960; yacc: 4,583; cs: 3,846; lex: 1,720; ruby: 1,002; php: 436; lisp: 258; awk: 105; sql: 66; sed: 53; csh: 10; exp: 6
file content (33 lines) | stat: -rw-r--r-- 1,099 bytes parent folder | download | duplicates (8) 
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
 
# What `#[derive(TryFrom)]` generates

Derive `TryFrom` allows you to convert enum discriminants into their corresponding variants.




## Enums

By default, a `TryFrom<isize>` is generated, matching the [type of the discriminant](https://doc.rust-lang.org/reference/items/enumerations.html#discriminants).
The type can be changed with a `#[repr(u/i*)]` attribute, e.g., `#[repr(u8)]` or `#[repr(i32)]`.
Only field-less variants can be constructed from their variant, therefore the `TryFrom` implementation will return an error for a discriminant representing a variant with fields.

```rust
# use derive_more::TryFrom;
#
#[derive(TryFrom, Debug, PartialEq)]
#[try_from(repr)]
#[repr(u32)]
enum Enum {
    ImplicitZero,
    ExplicitFive = 5,
    FieldSix(usize),
    EmptySeven{},
}

assert_eq!(Enum::ImplicitZero, Enum::try_from(0).unwrap());
assert_eq!(Enum::ExplicitFive, Enum::try_from(5).unwrap());
assert_eq!(Enum::EmptySeven{}, Enum::try_from(7).unwrap());

// Variants with fields are not supported, as the value for their fields would be undefined.
assert!(Enum::try_from(6).is_err());
```