cgp_field/types/
field.rs

1use core::fmt::Debug;
2use core::marker::PhantomData;
3
4/**
5   The `Field` type, a.k.a. `ω`, is used to represent a _named_ field entry
6   within a product type or a sum type.
7
8   `Field` is parameterized by a phantom `Tag` type, which is used to represent
9   the field name as type. Typically, this would either be a type-level string
10   such as `Symbol!("name")`, or a type-level index such as `Index<0>`.
11   Aside from that, `Field` is essentially a wrapper around `Value`.
12
13   `Field` is mainly used within the derived [`HasFields`](crate::traits::HasFields)
14   implementations, to include the field name in the generic product or sum
15   representation of the given struct or enum.
16
17   `Field` is also shown as `ω` to improve the readability of compiler error
18   messages. It is mainly useful when the type from `HasFields::Fields` is shown,
19   which would contain a lot of `Field`s and tend to take up a lot of screen space
20   to read.
21
22   ## Example
23
24   Given the following struct definition:
25
26   ```rust,ignore
27   #[derive(HasFields)]
28   pub struct MyContext {
29       pub name: String,
30       pub age: u8,
31   }
32   ```
33
34   The following `HasFields` implementation would be generated:
35
36   ```rust,ignore
37   impl HasFields for MyContext {
38       type Fields = Product![Field<Symbol!("name"), String>, Field<Symbol!("age"), u8>];
39   }
40   ```
41
42   which would be shown with the shortened representation as:
43
44   ```rust,ignore
45   impl HasFields for MyContext {
46       type Fields =
47           π<ω<Symbol!("name"), String>,
48               π<ω<Symbol!("age"), u8>,
49                   ε>>;
50   }
51   ```
52*/
53pub struct ω<Tag, Value> {
54    pub value: Value,
55    pub phantom: PhantomData<Tag>,
56}
57
58pub use ω as Field;
59
60impl<Tag, Value> From<Value> for Field<Tag, Value> {
61    fn from(value: Value) -> Self {
62        Self {
63            value,
64            phantom: PhantomData,
65        }
66    }
67}
68
69impl<Tag, Value> Debug for Field<Tag, Value>
70where
71    Value: Debug,
72{
73    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
74        self.value.fmt(f)
75    }
76}
77
78impl<Tag, Value> PartialEq for Field<Tag, Value>
79where
80    Value: PartialEq,
81{
82    fn eq(&self, other: &Self) -> bool {
83        self.value.eq(&other.value)
84    }
85}
86
87impl<Tag, Value> Eq for Field<Tag, Value>
88where
89    Value: Eq,
90{
91    fn assert_receiver_is_total_eq(&self) {
92        self.value.assert_receiver_is_total_eq()
93    }
94}
cgp_field/types/field.rs

cgp_field/types/
field.rs
