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Return the last element of an enum as Default in Rust
2019 Community Moderator ElectionHow do I exit a Rust program early from outside the main function?Why doesn't println! work in Rust unit tests?Allocating an object for C / FFI library callsHow to return reference to locally allocated struct/object? AKA error: `foo` does not live long enoughTrait to store structs with different generic parametersHow do you make a non-hashable, C-like enum from a library hashable?Class subtyping in RustClone for all-Clone structures with a non-Clone type parameterHow do I create a polymorphic array and then convert a value to the concrete type?Ownership and lifetime in nested iterators in rust for string comparison
I have a rust implementation as follows and in default implementation, for the enum, I need to return the last element and I need to achieve it without hardcoding it.
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub enum Region<CountryId>
None,
Category(CountryId),
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub struct Litrature1<CountryId>
pub Seek: Region<CountryId>,
pub Write: Region<CountryId>,
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub struct Litrature2<CountryId>
pub Seek: Region<CountryId>,
pub Write: Region<CountryId>,
pub Work: Region<CountryId>,
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub enum Alphabets<CountryId>
A1(Litrature1<CountryId>),
A2(Litrature1<CountryId>)
impl<CountryId> Default for Alphabets<CountryId>
fn default() -> Self
// How to return the last element of the enum as default?
Alphabets<CountryId>::A2
Playground
I am uncertain how to make this work
rust
edited 2 days ago
Akiner Alkan
1,518325
asked Mar 6 at 22:21
co2f2eco2f2e
5,984134989
add a comment |
I have a rust implementation as follows and in default implementation, for the enum, I need to return the last element and I need to achieve it without hardcoding it.
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub enum Region<CountryId>
None,
Category(CountryId),
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub struct Litrature1<CountryId>
pub Seek: Region<CountryId>,
pub Write: Region<CountryId>,
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub struct Litrature2<CountryId>
pub Seek: Region<CountryId>,
pub Write: Region<CountryId>,
pub Work: Region<CountryId>,
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub enum Alphabets<CountryId>
A1(Litrature1<CountryId>),
A2(Litrature1<CountryId>)
impl<CountryId> Default for Alphabets<CountryId>
fn default() -> Self
// How to return the last element of the enum as default?
Alphabets<CountryId>::A2
Playground
I am uncertain how to make this work
rust
edited 2 days ago
Akiner Alkan
1,518325
asked Mar 6 at 22:21
co2f2eco2f2e
5,984134989
YourAlphabetsenum variants each wrap around aLitratureXvalue, so what should the value of that be for your default implementation? Should it be a Literature1 withRegion::NoneforSeekandWrite?
– loganfsmyth
Mar 6 at 23:06
Yes , thats correct
– co2f2e
Mar 7 at 2:20
add a comment |
I have a rust implementation as follows and in default implementation, for the enum, I need to return the last element and I need to achieve it without hardcoding it.
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub enum Region<CountryId>
None,
Category(CountryId),
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub struct Litrature1<CountryId>
pub Seek: Region<CountryId>,
pub Write: Region<CountryId>,
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub struct Litrature2<CountryId>
pub Seek: Region<CountryId>,
pub Write: Region<CountryId>,
pub Work: Region<CountryId>,
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub enum Alphabets<CountryId>
A1(Litrature1<CountryId>),
A2(Litrature1<CountryId>)
impl<CountryId> Default for Alphabets<CountryId>
fn default() -> Self
// How to return the last element of the enum as default?
Alphabets<CountryId>::A2
Playground
I am uncertain how to make this work
rust
edited 2 days ago
Akiner Alkan
1,518325
asked Mar 6 at 22:21
co2f2eco2f2e
5,984134989
I have a rust implementation as follows and in default implementation, for the enum, I need to return the last element and I need to achieve it without hardcoding it.
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub enum Region<CountryId>
None,
Category(CountryId),
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub struct Litrature1<CountryId>
pub Seek: Region<CountryId>,
pub Write: Region<CountryId>,
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub struct Litrature2<CountryId>
pub Seek: Region<CountryId>,
pub Write: Region<CountryId>,
pub Work: Region<CountryId>,
#[cfg_attr(feature = "std", derive(Debug))]
#[derive(Clone, PartialEq, Eq)]
pub enum Alphabets<CountryId>
A1(Litrature1<CountryId>),
A2(Litrature1<CountryId>)
impl<CountryId> Default for Alphabets<CountryId>
fn default() -> Self
// How to return the last element of the enum as default?
Alphabets<CountryId>::A2
Playground
I am uncertain how to make this work
rust
rust
edited 2 days ago
Akiner Alkan
1,518325
asked Mar 6 at 22:21
co2f2eco2f2e
5,984134989
edited 2 days ago
Akiner Alkan
1,518325
asked Mar 6 at 22:21
co2f2eco2f2e
5,984134989
edited 2 days ago
Akiner Alkan
1,518325
edited 2 days ago
Akiner Alkan
1,518325
edited 2 days ago
Akiner Alkan
1,518325
1,518325
asked Mar 6 at 22:21
co2f2eco2f2e
5,984134989
asked Mar 6 at 22:21
co2f2eco2f2e
5,984134989
asked Mar 6 at 22:21
co2f2eco2f2e
5,984134989
5,984134989
YourAlphabetsenum variants each wrap around aLitratureXvalue, so what should the value of that be for your default implementation? Should it be a Literature1 withRegion::NoneforSeekandWrite?
– loganfsmyth
Mar 6 at 23:06
Yes , thats correct
– co2f2e
Mar 7 at 2:20
add a comment |
YourAlphabetsenum variants each wrap around aLitratureXvalue, so what should the value of that be for your default implementation? Should it be a Literature1 withRegion::NoneforSeekandWrite?
– loganfsmyth
Mar 6 at 23:06
Yes , thats correct
– co2f2e
Mar 7 at 2:20
Your
Alphabets enum variants each wrap around a LitratureX value, so what should the value of that be for your default implementation? Should it be a Literature1 with Region::None for Seek and Write?– loganfsmyth
Mar 6 at 23:06
Your
Alphabets enum variants each wrap around a LitratureX value, so what should the value of that be for your default implementation? Should it be a Literature1 with Region::None for Seek and Write?– loganfsmyth
Mar 6 at 23:06
Yes , thats correct
– co2f2e
Mar 7 at 2:20
Yes , thats correct
– co2f2e
Mar 7 at 2:20
add a comment |
1 Answer
1
active
oldest
votes
I'm assuming that you essentially want default values all the way down, where each region defaults to Region::None. In that context, it would make the most sense to define Default on each nested type, e.g.
Default for Region
impl<CountryId> Default for Region<CountryId>
fn default() -> Self
Region::None
Default for Litrature1
impl<CountryId> Default for Litrature1<CountryId>
fn default() -> Self
Litrature1
Seek: Default::default(),
Write: Default::default(),
Default for Litrature2
impl<CountryId> Default for Litrature2<CountryId>
fn default() -> Self
Litrature2
Seek: Default::default(),
Write: Default::default(),
Work: Default::default(),
Default for Alphabets
impl<CountryId> Default for Alphabets<CountryId>
fn default() -> Self
Alphabets::A2(Default::default())
(On the Rust playground)
answered Mar 6 at 23:12
loganfsmythloganfsmyth
105k21223187
Or you could just deriveDefault
– mcarton
Mar 7 at 1:25
@loganfsmyth Rather than Hardcoding the last item as ::A2 Im looking for a dynamic way to get the last item Thanks
– co2f2e
Mar 7 at 2:18
1
@mcarton Unfortunately that would requireCountryIdto implementDefaultbecause of github.com/rust-lang/rust/issues/26925.
– loganfsmyth
2 days ago
2
@co2f2e Would something like github.com/idanarye/rust-smart-default work? There's nothing special about the last variant of an enum, so it's it's not something that would be built in.
– loganfsmyth
2 days ago
add a comment |
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1 Answer
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oldest
votes
I'm assuming that you essentially want default values all the way down, where each region defaults to Region::None. In that context, it would make the most sense to define Default on each nested type, e.g.
Default for Region
impl<CountryId> Default for Region<CountryId>
fn default() -> Self
Region::None
Default for Litrature1
impl<CountryId> Default for Litrature1<CountryId>
fn default() -> Self
Litrature1
Seek: Default::default(),
Write: Default::default(),
Default for Litrature2
impl<CountryId> Default for Litrature2<CountryId>
fn default() -> Self
Litrature2
Seek: Default::default(),
Write: Default::default(),
Work: Default::default(),
Default for Alphabets
impl<CountryId> Default for Alphabets<CountryId>
fn default() -> Self
Alphabets::A2(Default::default())
(On the Rust playground)
answered Mar 6 at 23:12
loganfsmythloganfsmyth
105k21223187
Or you could just deriveDefault
– mcarton
Mar 7 at 1:25
@loganfsmyth Rather than Hardcoding the last item as ::A2 Im looking for a dynamic way to get the last item Thanks
– co2f2e
Mar 7 at 2:18
1
@mcarton Unfortunately that would requireCountryIdto implementDefaultbecause of github.com/rust-lang/rust/issues/26925.
– loganfsmyth
2 days ago
2
@co2f2e Would something like github.com/idanarye/rust-smart-default work? There's nothing special about the last variant of an enum, so it's it's not something that would be built in.
– loganfsmyth
2 days ago
add a comment |
I'm assuming that you essentially want default values all the way down, where each region defaults to Region::None. In that context, it would make the most sense to define Default on each nested type, e.g.
Default for Region
impl<CountryId> Default for Region<CountryId>
fn default() -> Self
Region::None
Default for Litrature1
impl<CountryId> Default for Litrature1<CountryId>
fn default() -> Self
Litrature1
Seek: Default::default(),
Write: Default::default(),
Default for Litrature2
impl<CountryId> Default for Litrature2<CountryId>
fn default() -> Self
Litrature2
Seek: Default::default(),
Write: Default::default(),
Work: Default::default(),
Default for Alphabets
impl<CountryId> Default for Alphabets<CountryId>
fn default() -> Self
Alphabets::A2(Default::default())
(On the Rust playground)
answered Mar 6 at 23:12
loganfsmythloganfsmyth
105k21223187
Or you could just deriveDefault
– mcarton
Mar 7 at 1:25
@loganfsmyth Rather than Hardcoding the last item as ::A2 Im looking for a dynamic way to get the last item Thanks
– co2f2e
Mar 7 at 2:18
1
@mcarton Unfortunately that would requireCountryIdto implementDefaultbecause of github.com/rust-lang/rust/issues/26925.
– loganfsmyth
2 days ago
2
@co2f2e Would something like github.com/idanarye/rust-smart-default work? There's nothing special about the last variant of an enum, so it's it's not something that would be built in.
– loganfsmyth
2 days ago
add a comment |
I'm assuming that you essentially want default values all the way down, where each region defaults to Region::None. In that context, it would make the most sense to define Default on each nested type, e.g.
Default for Region
impl<CountryId> Default for Region<CountryId>
fn default() -> Self
Region::None
Default for Litrature1
impl<CountryId> Default for Litrature1<CountryId>
fn default() -> Self
Litrature1
Seek: Default::default(),
Write: Default::default(),
Default for Litrature2
impl<CountryId> Default for Litrature2<CountryId>
fn default() -> Self
Litrature2
Seek: Default::default(),
Write: Default::default(),
Work: Default::default(),
Default for Alphabets
impl<CountryId> Default for Alphabets<CountryId>
fn default() -> Self
Alphabets::A2(Default::default())
(On the Rust playground)
answered Mar 6 at 23:12
loganfsmythloganfsmyth
105k21223187
I'm assuming that you essentially want default values all the way down, where each region defaults to Region::None. In that context, it would make the most sense to define Default on each nested type, e.g.
Default for Region
impl<CountryId> Default for Region<CountryId>
fn default() -> Self
Region::None
Default for Litrature1
impl<CountryId> Default for Litrature1<CountryId>
fn default() -> Self
Litrature1
Seek: Default::default(),
Write: Default::default(),
Default for Litrature2
impl<CountryId> Default for Litrature2<CountryId>
fn default() -> Self
Litrature2
Seek: Default::default(),
Write: Default::default(),
Work: Default::default(),
Default for Alphabets
impl<CountryId> Default for Alphabets<CountryId>
fn default() -> Self
Alphabets::A2(Default::default())
(On the Rust playground)
answered Mar 6 at 23:12
loganfsmythloganfsmyth
105k21223187
answered Mar 6 at 23:12
loganfsmythloganfsmyth
105k21223187
answered Mar 6 at 23:12
loganfsmythloganfsmyth
105k21223187
answered Mar 6 at 23:12
loganfsmythloganfsmyth
105k21223187
105k21223187
Or you could just deriveDefault
– mcarton
Mar 7 at 1:25
@loganfsmyth Rather than Hardcoding the last item as ::A2 Im looking for a dynamic way to get the last item Thanks
– co2f2e
Mar 7 at 2:18
1
@mcarton Unfortunately that would requireCountryIdto implementDefaultbecause of github.com/rust-lang/rust/issues/26925.
– loganfsmyth
2 days ago
2
@co2f2e Would something like github.com/idanarye/rust-smart-default work? There's nothing special about the last variant of an enum, so it's it's not something that would be built in.
– loganfsmyth
2 days ago
add a comment |
Or you could just deriveDefault
– mcarton
Mar 7 at 1:25
@loganfsmyth Rather than Hardcoding the last item as ::A2 Im looking for a dynamic way to get the last item Thanks
– co2f2e
Mar 7 at 2:18
1
@mcarton Unfortunately that would requireCountryIdto implementDefaultbecause of github.com/rust-lang/rust/issues/26925.
– loganfsmyth
2 days ago
2
@co2f2e Would something like github.com/idanarye/rust-smart-default work? There's nothing special about the last variant of an enum, so it's it's not something that would be built in.
– loganfsmyth
2 days ago
Or you could just derive
Default– mcarton
Mar 7 at 1:25
Or you could just derive
Default– mcarton
Mar 7 at 1:25
@loganfsmyth Rather than Hardcoding the last item as ::A2 Im looking for a dynamic way to get the last item Thanks
– co2f2e
Mar 7 at 2:18
@loganfsmyth Rather than Hardcoding the last item as ::A2 Im looking for a dynamic way to get the last item Thanks
– co2f2e
Mar 7 at 2:18
1
1
@mcarton Unfortunately that would require
CountryId to implement Default because of github.com/rust-lang/rust/issues/26925.– loganfsmyth
2 days ago
@mcarton Unfortunately that would require
CountryId to implement Default because of github.com/rust-lang/rust/issues/26925.– loganfsmyth
2 days ago
2
2
@co2f2e Would something like github.com/idanarye/rust-smart-default work? There's nothing special about the last variant of an enum, so it's it's not something that would be built in.
– loganfsmyth
2 days ago
@co2f2e Would something like github.com/idanarye/rust-smart-default work? There's nothing special about the last variant of an enum, so it's it's not something that would be built in.
– loganfsmyth
2 days ago
add a comment |
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Your
Alphabetsenum variants each wrap around aLitratureXvalue, so what should the value of that be for your default implementation? Should it be a Literature1 withRegion::NoneforSeekandWrite?– loganfsmyth
Mar 6 at 23:06
Yes , thats correct
– co2f2e
Mar 7 at 2:20