Macro non_exhaustive::non_exhaustive

macro_rules! non_exhaustive {
    {$type:ty {$($field:ident: $value:expr,)* ..$default:expr}} => { ... };
    {$type:ty {$($field:ident: $value:expr),* $(,)?}} => { ... };
}

Macro to create non_exhaustive structs and structs with private fields with the functional update syntax, i.e., using ..Default::default().

Given the foreign structs:

#[non_exhaustive]
#[derive(Default)]
pub struct NonExhaustive {
  pub field: usize
}

#[derive(Default)]
pub struct PrivateFields {
  pub pub_field: usize,
  private_field: usize
}

The following is not possible:

NonExhaustive {
  field: 1,
  ..Default::default()
};

PrivateFields {
  pub_field: 1,
  ..Default::default()
};

non_exhaustive! remedies that:

use non_exhaustive::non_exhaustive;

non_exhaustive! {NonExhaustive {
  field: 1,
  ..Default::default()
}};

non_exhaustive! {PrivateFields {
  pub_field: 1,
  ..Default::default()
}};

For the common case of using Default::default(), non_exhaustive! allows omitting the ..expression:

use non_exhaustive::non_exhaustive;

non_exhaustive!(NonExhaustive { field: 1 });
non_exhaustive!(PrivateFields { pub_field: 1 });

Under the hood, non_exhaustive! is extremely simple, it expands to:

{
  let mut value: NonExhaustive = Default::default();
  value.field = 1;
  value
};