enumcapsulate 0.6.3

Safe casting for newtype enums and their variants
Documentation 
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

use enumcapsulate::AsVariant;

trait HasAssoc {
    type Assoc: Sized;
}

#[derive(Clone)]
pub struct VariantA;
#[derive(Clone)]
pub struct VariantB;
#[derive(Clone)]
pub struct VariantC<'l>(&'l ());
#[derive(Clone)]
pub struct VariantD<const N: usize>([(); N]);
#[derive(Clone)]
pub struct VariantE<T>(T);
#[derive(Clone)]
pub struct VariantF<'l, const N: usize, T>(&'l [T; N]);

#[derive(Clone)]
pub struct VariantT;

impl HasAssoc for VariantT {
    type Assoc = ();
}

#[derive(Clone)]
pub struct VariantU;

trait HasT {
    // This associated type intentionally has the same name
    // as the generic type param of the enum subject.
    //
    // The point of this is to detect false positives
    // from the generic param detection, which should falsely
    // detect `VariantU::T` as a use of the type param `T`:
    type T: Sized;
}

impl HasT for VariantU {
    type T = ();
}

#[derive(AsVariant)]
pub enum Enum<'l, const N: usize, T>
where
    T: HasAssoc,
{
    Unit,
    // We expect this variant to get derived:
    OwnedSpecificType(VariantA),
    // We expect this variant to get derived:
    BorrowedSpecificType(&'l VariantB),
    // We expect this variant to get derived:
    OwnedWithGenericLifetime(VariantC<'l>),
    // We expect this variant to NOT get derived (due to its use of a const param):
    OwnedGenericTypeWithConstParam(VariantD<N>),
    // We expect this variant to NOT get derived (due to its use of a type param):
    OwnedGenericTypeWithTypeParam(VariantE<T>),
    // We expect this variant to NOT get derived (due to its use of const and type params):
    OwnedGenericTypeWithMixedParams(VariantF<'l, N, T>),
    // We expect this variant to NOT get derived (due to its use of a type param):
    OwnedGenericParam(T),
    // We expect this variant to NOT get derived (due to its use of a type param):
    BorrowedGenericParam(&'l T),
    // We expect this variant to NOT get derived (due to its use of a type param):
    OwnedAssocTypeOfGenericParam(T::Assoc),
    // We expect this variant to NOT get derived (due to its use of a type param):
    OwnedAssocTypeOfGenericParamBehindCast(<T as HasAssoc>::Assoc),
    // We expect this variant to get derived:
    OwnedAssocTypeOfSpecificTypeBehindCast(<VariantU as HasT>::T),
}

fn main() {
    type Subject<'x> = Enum<'x, 42, VariantT>;

    let mut subject = Subject::Unit;

    let _: Option<VariantA> = subject.as_variant();
    let _: Option<&VariantB> = subject.as_variant();
    let _: Option<VariantC<'_>> = subject.as_variant();
    let _: Option<VariantC<'_>> = subject.as_variant();
    let _: Option<<VariantU as HasT>::T> = subject.as_variant();
}