Crate impl_index
source ·Expand description
A macro for deriving Index
& IndexMut
implementations.
Basic usage
// Derive only Index
index!(Struct by Enum => Output:
Variant1 => field1,
Variant2 => field2,
);
// Derive Index and IndexMut
index!(Struct by Enum => mut Output:
Variant1 => field1,
Variant2 => field2,
);
// Match/get by pattern
index!(Struct by Enum => Output:
pat Enum::Variant(Foo::Bar) => field1,
pat Enum::Index(idx) => pat field2[idx],
);
Example
use impl_index::index;
#[derive(Default)]
struct Struct {
a: u8,
arr: [u8; 10],
thing_1: u8,
thing_2: u8,
}
enum Enum {
A,
Arr(usize),
Thing(Thing),
}
enum Thing {
One,
Two,
}
index!(Struct by Enum => mut u8:
A => a,
pat Enum::Arr(idx) if idx < 10 => pat arr[idx],
pat Enum::Thing(Thing::One) => thing_1,
pat _ => thing_2,
);
let mut s = Struct::default();
s[Enum::A] = 1;
for idx in 0u8..10 {
s[Enum::Arr(idx.into())] = idx * 10;
}
s[Enum::Thing(Thing::One)] = 200;
s[Enum::Thing(Thing::Two)] = 201;
assert_eq!(s[Enum::A], 1, "A");
for idx in 0u8..10 {
assert_eq!(s[Enum::Arr(idx.into())], idx * 10, "Arr({})", idx);
}
assert_eq!(s[Enum::Thing(Thing::One)], 200, "Thing(One)");
assert_eq!(s[Enum::Thing(Thing::Two)], 201, "Thing(Two)");
Generated output
#[automatically_derived]
impl ::core::ops::Index<Enum> for Struct {
type Output = u8;
fn index(&self, index_macro_derived_index_input: Enum) -> &Self::Output {
match index_macro_derived_index_input {
Enum::A => &self.a,
Enum::Arr(idx) if idx < 10 => &self.arr[idx],
Enum::Thing(Thing::One) => &self.thing_1,
_ => &self.thing_2,
}
}
}
#[automatically_derived]
impl ::core::ops::IndexMut<Enum> for Struct {
fn index_mut(&mut self, index_macro_derived_index_input: Enum) -> &mut Self::Output {
match index_macro_derived_index_input {
Enum::A => &mut self.a,
Enum::Arr(idx) if idx < 10 => &mut self.arr[idx],
Enum::Thing(Thing::One) => &mut self.thing_1,
_ => &mut self.thing_2,
}
}
}
Example without generating IndexMut
This will fail to compile on instance[Idx::Foo] = 1;
ⓘ
struct Struct {
foo: usize,
}
enum Idx {
Foo,
}
index!(Struct by Idx => usize: Foo => foo);
let mut instance = Struct { foo: 0 };
instance[Idx::Foo] = 1;