former 2.44.0

A flexible implementation of the Builder pattern supporting nested builders and collection-specific subformers. Simplify the construction of complex objects.
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//! This example demonstrates how to create custom former definitions with ending callbacks.

#![allow(missing_docs)]

// ## Example : Custom Definition
//
// Define a custom former definition and custom forming logic, and apply them to a collection.
//
// The example showcases how to accumulate elements into a collection and then transform them into a single result
// using a custom `FormingEnd` implementation. This pattern is useful for scenarios where the formation process
// involves aggregation or transformation of input elements into a different type or form.

//#[cfg(not(all(
//  feature = "enabled",
//  feature = "derive_former",
//  any(feature = "use_alloc", not(feature = "no_std"))
//)))]
//fn main() {}

//#[cfg(all(
//  feature = "enabled",
//  feature = "derive_former",
//  any(feature = "use_alloc", not(feature = "no_std"))
//))]
fn main() {
  // Define a struct `Sum` that will act as a custom former definition.
  struct Sum;

  // Implement `FormerDefinitionTypes` for `Sum`.
  // This trait defines the types used during the forming process.
  impl former::FormerDefinitionTypes for Sum {
    type Storage = Vec<i32>; // Collection for the integers.
    type Formed = i32; // The final type after forming, which is a single integer.
    type Context = (); // No additional context is used in this example.
  }

  // Implement `FormerMutator` for `Sum`.
  // This trait could include custom mutation logic applied during the forming process, but it's empty in this example.
  impl former::FormerMutator for Sum {}

  // Implement `FormerDefinition` for `Sum`.
  // This trait links the custom types to the former.
  impl former::FormerDefinition for Sum {
    type Types = Sum; // Associate the `FormerDefinitionTypes` with `Sum`.
    type End = Sum; // Use `Sum` itself as the end handler.
    type Storage = Vec<i32>; // Specify the storage type.
    type Formed = i32; // Specify the final formed type.
    type Context = (); // Specify the context type, not used here.
  }

  // Implement `FormingEnd` for `Sum`.
  // This trait handles the final step of the forming process.
  impl former::FormingEnd<Sum> for Sum {
    fn call(
      &self,
      storage: <Sum as former::FormerDefinitionTypes>::Storage,
      _context: Option<<Sum as former::FormerDefinitionTypes>::Context>,
    ) -> <Sum as former::FormerDefinitionTypes>::Formed {
      // Sum all integers in the storage vector.
      storage.iter().sum()
    }
  }

  // Use the custom `Former` to sum a list of integers.
  let got = former::CollectionFormer::<i32, Sum>::new(Sum)
  .add( 1 )  // Add an integer to the storage.
  .add( 2 )  // Add another integer.
  .add( 10 ) // Add another integer.
  .form(); // Perform the form operation, which triggers the summing logic.
  let exp = 13; // Expected result after summing 1, 2, and 10.
  assert_eq!(got, exp); // Assert the result is as expected.

  dbg!(got); // Debug print the result to verify the output.
             // > got = 13
}