Get-field-by-type

Create a getter for a field based on its type. For example

```rust use getfieldby_type::GetFieldByType;

[derive(GetFieldByType)]

[getfieldbytypetarget(i32)]

enum Enum1 { A(i32, char), B(i32, bool), C(i32, String) }

let x = Enum1::A(12, '!'); assert_eq!(*GetFieldByType::::get(&x), 12); ```

Why not impl &Self for Into<&T>

Using Into on references for getting a field is a bit of hack. This is designed for getting the value for a field with a common type. Using a custom trait also means flexibility in the future

Additional options and features

When a struct of variant doesn't have a type, there are two behaviors

Either a compile time error (default)

Or a specified statement to evaluate. This could be a panic

```rust use getfieldby_type::GetFieldByType;

[derive(GetFieldByType)]

[getfieldbytypetarget(i32)]

[getfieldnotypebehavior(panic!("could not find item");)]

enum Enum2 { A(i32), B(i32), C }

assert_eq!(*GetFieldByType::::get(&Enum2::A(12)), 12);

let result = std::panic::catchunwind(|| { let _value = *GetFieldByType::::get(&Enum2::C); }); assert!(result.iserr()); ```

or returning a constant value

```rust use getfieldby_type::GetFieldByType;

[derive(GetFieldByType)]

[getfieldbytypetarget(i32)]

[getfieldnotypebehavior(return &0;)]

enum Enum2 { A(i32), B(i32), C }

asserteq!(*GetFieldByType::::get(&Enum2::A(12)), 12); asserteq!(*GetFieldByType::::get(&Enum2::C), 0); ```

Recursive on unit variants

In the AOrB enum case, the derive macro can't find a i32 on variant AOrB::A. However, as it is a unit variant, the implementation delegates it to the unit type.

```rust use getfieldby_type::GetFieldByType;

[derive(GetFieldByType)]

[getfieldbytypetarget(i32)]

struct A(pub i32);

[derive(GetFieldByType)]

[getfieldbytypetarget(i32)]

struct B(pub i32);

[derive(GetFieldByType)]

[getfieldbytypetarget(i32)]

enum AOrB { A(A), B(B) }

let b = B(10); assert_eq!(*GetFieldByType::::get(&b), 10);

let aorb = AOrB::B(b); asserteq!(*GetFieldByType::::get(&aor_b), 10); ```

Alternatives

For more manual field access, check out getset. If looking for getting multiple fields, check out getters-by-type