Derive Macro Assign

#[derive(Assign)]
{
    // Attributes available to this derive:
    #[debug]
}

Derives the Assign trait for struct fields, allowing each field to be set with a value that can be converted into the field’s type.

This macro facilitates the automatic implementation of the Assign trait for all fields within a struct, leveraging the power of Rust’s type system to ensure type safety and conversion logic. It is particularly useful for builder patterns or mutating instances of data structures in a fluent and ergonomic manner.

Attributes

• debug : An optional attribute to enable debugging of the trait derivation process.

Conditions

• This macro is only enabled when the derive_component_assign feature is active in your Cargo.toml.

Input Code Example

Given a struct definition annotated with #[ derive( Assign ) ] :

use component_model_types::Assign;
use component_model_meta::Assign;

#[ derive( Default, PartialEq, Debug, Assign ) ]
struct Person
{
  age : i32,
  name : String,
}

let mut person : Person = Default::default();
person.assign( 13 );
person.assign( "John" );
assert_eq!( person, Person { age : 13, name : "John".to_string() } );

Generated Code Example

The procedural macro generates the following implementations for Person :

use component_model_types::Assign;
use component_model_meta::Assign;

#[ derive( Default, PartialEq, Debug ) ]
struct Person
{
  age : i32,
  name : String,
}

impl< IntoT > Assign< i32, IntoT > for Person
where
  IntoT : Into< i32 >,
{
  fn assign( &mut self, component : IntoT )
  {
    self.age = component.into();
  }
}

impl< IntoT > Assign< String, IntoT > for Person
where
  IntoT : Into< String >,
{
  fn assign( &mut self, component : IntoT )
  {
    self.name = component.into();
  }
}

let mut person : Person = Default::default();
person.assign( 13 );
person.assign( "John" );
assert_eq!( person, Person { age : 13, name : "John".to_string() } );

This allows any type that can be converted into an i32 or String to be set as the value of the age or name fields of Person instances, respectively.