r3bl_rs_utils 0.9.3

/*
 *   Copyright (c) 2022 R3BL LLC
 *   All rights reserved.
 *
 *   Licensed under the Apache License, Version 2.0 (the "License");
 *   you may not use this file except in compliance with the License.
 *   You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 *   Unless required by applicable law or agreed to in writing, software
 *   distributed under the License is distributed on an "AS IS" BASIS,
 *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *   See the License for the specific language governing permissions and
 *   limitations under the License.
 */

pub trait LazyExecutor<T>
where
    T: Send + Sync,
{
    fn compute(&mut self) -> T;

    /// Book: <https://doc.rust-lang.org/book/ch10-02-traits.html>
    #[allow(clippy::all)]
    fn new() -> Box<dyn LazyExecutor<T> + Send + Sync>
    where
        Self: Default + Sized + Sync + Send + 'static,
    {
        Box::new(Self::default())
    }
}

pub struct LazyField<T>
where
    T: Send + Sync,
{
    pub lazy_executor: Box<dyn LazyExecutor<T> + Send + Sync>,
    pub field: T,
    pub has_computed: bool,
}

impl<T> LazyField<T>
where
    T: Send + Sync,
    T: Default + Clone,
{
    pub fn new(lazy_executor: Box<dyn LazyExecutor<T> + Send + Sync>) -> Self {
        Self {
            lazy_executor,
            field: T::default(),
            has_computed: false,
        }
    }

    pub fn compute(&mut self) -> T {
        if self.has_computed {
            self.field.clone()
        } else {
            self.field = self.lazy_executor.compute();
            self.has_computed = true;
            self.field.clone()
        }
    }
}