functional_builder.rs

#[derive(Debug)]
struct Person
{
  name: String,
  position: String
}

impl Default for Person
{
  fn default() -> Self {
    Person{
      name: "".to_string(),
      position: "".to_string() }
  }
}

struct FunctionalBuilder<TSubject>
  where TSubject : Default
{
  actions: Vec<Box<dyn Fn(&mut TSubject) -> ()>>
}

impl<TSubject> FunctionalBuilder<TSubject>
  where TSubject : Default
{
  fn build(self) -> TSubject
  {
    let mut subj = TSubject::default();
    for action in self.actions
    {
      (*action)(&mut subj);
    }
    subj
  }

  fn new() -> FunctionalBuilder<TSubject>
  {
    Self {
      actions: Vec::new()
    }
  }
}

struct PersonBuilder
{
  builder: FunctionalBuilder::<Person>
}

impl PersonBuilder
{
  pub fn new() -> Self {
    PersonBuilder { builder: FunctionalBuilder::<Person>::new() }
  }

  pub fn called(mut self, name: &str) -> PersonBuilder
  {
    let value = name.to_string();
    self.builder.actions.push(Box::new(move |x| {
      x.name = value.clone();
    }));
    self
  }

  pub fn build(self) -> Person
  {
    self.builder.build()
  }
}

pub fn demo()
{
  let builder = PersonBuilder::new();
  let me = builder
    .called("Dmitri")
    .build();
  println!("{:?}", me);
}