impl_trait_for_FnOnce_type.rs

use std::error::Error;

type Result<T> = std::result::Result<T, Box<dyn Error>>;
pub trait Parser: Sized {
    type Output;
    fn parse(self) -> Result<Self::Output>;
}

impl<F, T> Parser for F
where
    F: FnOnce() -> Result<T>, // fn -> Fn -> FnMut -> FnOnce
{
    type Output = T;

    fn parse(self) -> Result<Self::Output> {
        todo!()
    }
}

pub trait ParseMacroInput: Sized {
    fn parse() -> Result<Self>;
}

impl<T> ParseMacroInput for T {
    fn parse() -> Result<Self> {
        todo!()
    }
}

pub fn parse<T: ParseMacroInput>() -> Result<T> {
    let x = T::parse; // fn parse<T>() -> Result<T>, x is a function pointer
    x.parse() // The Parser trait is implemented for all pointer of functions that return a Result
}

// mod modular_err;