Macro stateful_processor 

macro_rules! stateful_processor {
    ($struct_name:ident, $state_type:ty, $type:ty, $process_fn:expr) => { ... };
    ($struct_name:ident, $state_type:ty, $state_value:expr, $type:ty, $process_fn:expr) => { ... };
}

Creates a stateful processor that maintains its own internal state.

This macro generates a struct that implements StatefulProcessor<T>. The processing logic can read and modify the internal state during its operation.

Two variants are available:

1. Takes a state type and requires the state to be provided via a new() constructor.
2. Takes a state type and an initial value expression, providing a new() constructor with no arguments.

Arms

1. With new(state) constructor

• $struct_name: Name of the processor struct.
• $state_type: Type of the internal state.
• $type: Type of the data to be processed.
• $process_fn: A closure |state, data| -> new_data.

2. With new() constructor and initial state

• $struct_name: Name of the processor struct.
• $state_type: Type of the internal state.
• $state_value: An expression that evaluates to the initial state.
• $type: Type of the data to be processed.
• $process_fn: A closure |state, data| -> new_data.

Examples

1. With new(state)

use type_flow_macros::stateful_processor;
use type_flow_traits::StatefulProcessor;

// A processor that adds a configurable number to the input.
stateful_processor!(AddN, i32, i32, |state: &mut i32, data: i32| {
    data + *state
});

let mut processor = AddN::new(5); // State is 5
assert_eq!(processor.process(10), 15);
assert_eq!(processor.process(20), 25); // State remains 5

2. With initial state value

use type_flow_macros::stateful_processor;
use type_flow_traits::StatefulProcessor;
// A processor that accumulates values.
stateful_processor!(Accumulator, i32, 0, i32, |state: &mut i32, data: i32| {
    *state += data;
    *state // returns the new accumulated value
});

let mut processor = Accumulator::new();
assert_eq!(processor.process(5), 5);
assert_eq!(processor.process(10), 15);
assert_eq!(processor.process(-3), 12);