Bits: Generic Rust

  fn demo_std_generic_types() {

  show_label("demo standard generic types", 32);
  println!();

  show_op("arrays: [T; N]");
  println!();
  let arri = [1, 2, 3, 2, 1];
  println!("  {:?}", arri);
  let arrf = [1.0, 1.5, 2.0, 1.5, 1.0];
  println!("  {:?}\n", arrf);

  show_op("slices: &T[m..n]");
  println!();
  let slicei = &arri[1..5]; // [2, 3, 4, 5]
  println!("  {:?}", slicei);
  let slicef = &arrf[2..4]; // [2.0, 1.5]
  println!("  {:?}\n", slicef);

  show_op("vectors: Vec<T>");
  println!();

  /*-- vector of copy type --*/
  let mut v = Vec::<i32>::new();
  let s = &vec![1, 2, 3, 2, 1];
  v.extend_from_slice(s);
  /*
  This works because the elements are i32, i.e., copy.
  To load a vector with non-copy types use:
  v.extend(s.iter().cloned());
  */
  println!("  Vec<i32> {:?}", v);

  /*--- vector of tuple (i32, &str) --*/
  let mut v2 = Vec::<(i32,&str)>::new();
  v2.push((1, "one"));
  v2.push((2, "two"));
  println!("  Vec<(i32, &str)> {:?}\n", v2);

  show_op("maps: HashMap<K,V>");
  println!();
  let mut m = HashMap::<&str, i32>::new();
  m.insert("zero", 0);
  m.insert("one", 1);
  m.insert("two", 2);
  m.insert("three", 3);
  println!("  maps: HashMap<&str, i32>");
  println!("    {:?}", m);
  }

/*---------------------------------------------------------
  HelloGeneric: user-defined generic type
  - Not very useful except as a demonstration of how
    to create a generic type.
  - HelloGeneric instances hold a single value of T
  - Generic parameter T is required to implement traits
      Debug   - supports using debug format {:?}
      Default - supports using a default value, T:default()
      Clone   - implements a copy of an instance with clone()
  - Specified traits, like those above, are often called
    bounds because they limit the types that can be used
    as function and method arguments.
*/
#[derive(Debug, Clone)]  // compiler generated code
struct HelloGeneric<T>
  where T: Debug + Default + Clone
{
  datum: T,
}
impl<T> HelloGeneric<T>
  where T: Debug + Default + Clone
{
  /* construct new instance with datum = d */
  fn new(d:T) -> Self {
    HelloGeneric::<T> {
      datum: d,
    }
  }
  /* construct new instance with default data value */
  fn default_new() -> Self {
    HelloGeneric::<T> {
      datum: T::default(),
    }
  }
  /*
    As shown, value() is equivalent to making datum public.
    However value method supports adding code to modify the
    return value.
  */
  fn value(&mut self) -> &mut T {
    &mut self.datum
  }
  /* print representation of an instance */
  fn show(&self) {
    println!("  HelloGeneric {{ {:?} }}", self.datum);
  }
}

/*---------------------------------------------------------
  Demonstrate creation of HelloGeneric type and use
  of its methods.
*/
#[allow(non_snake_case)]
pub fn demo_HelloGeneric() {

  show_label(" demo user defined HelloGeneric type", 40);
  println!();
  show_op("HelloGeneric<T>");
  println!();

  show_op("let mut h = HelloGeneric::<i32>::new(42)");
  let mut h = HelloGeneric::<i32>::new(42);
  h.show();
  println!();

  show_op("*h.value() = 84");
  *h.value() = 84;
  h.show();
  println!();

  show_op("let c = h.clone()");
  let c = h.clone();  // h still valid
  c.show();
  println!();

  show_op("let n = h : transfer ownership of datum");
  let n = h;  // move ownership of datum to h
  n.show();

  //h.show();  // h invalid, been moved
}

/*-------------------------------------------------------------------
  stats.rs
  - defines type Stats containing Vec of generic Type
    bounded by Arithmetic trait
  - Works as is only for i32 and f64, but easy to extend to
    all integers and floats
  - Can also be extended to complex numbers
-------------------------------------------------------------------*/

use std::ops::*;
use std::cmp::*;
use std::convert::{Into};
use std::fmt::Debug;

pub trait Arithmetic<T = Self>: Add<Output=T> + Sub<Output=T>
    + Mul<Output=T> + Div<Output=T> + PartialEq + PartialOrd
    + Default + Copy + Debug + Into<f64> {}

impl Arithmetic<f64> for f64 {}
impl Arithmetic<i32> for i32 {}

#[derive(Debug, Clone)]
pub struct Stats<T: Arithmetic + Debug> {
  items: Vec<T>
}

impl<T: Arithmetic> Stats<T>
    where T: Arithmetic + Debug
{
  pub fn new(v:Vec<T>) -> Stats<T> {
    Stats {
      items: v,
    }
  }
  pub fn max(&self) -> T {
    let mut biggest = self.items[0];
    for item in &self.items {
      if biggest < *item {
        biggest = *item;
      }
    }
    biggest
  }
  pub fn min(&self) -> T {
    let mut smallest = self.items[0];
    for item in &self.items {
      if smallest > *item {
        smallest = *item;
      }
    }
    smallest
  }
  pub fn sum(&self) -> T {
    let mut sum = T::default();
    for item in &self.items {
      sum = sum + *item;
    }
    sum
  }
  pub fn avg(&self) -> f64 {
    let mut sum = T::default();
    for item in &self.items {
      sum = sum + *item;
    }
    /*-- cast usize to f64 --*/
    let den:f64 = self.items.len() as f64;
    /*-- can't cast non-primitive to primitive --*/
    let num:f64 = sum.into();
    num/den
  }
}

/*---------------------------------------------------------
  Demonstrate user-defined Stats<T> type
*/
pub fn demo_stats() {
  show_label("demo Arithmetic Trait with Stats<T>", 40);
  println!();

  show_op("Stats<T>");
  println!();
  let s = Stats::<f64>::new(vec![1.5, 2.5, 3.0, -1.25, 0.5]);
  println!("  {:?}", s);
  println!("  max: {:?}", s.max());
  println!("  min: {:?}", s.min());
  println!("  sum: {:?}", s.sum());
  println!("  avg: {:?}", s.avg());
}

/*-------------------------------------------------------------------
  points_generic.rs
  - defines type Point<T, N>
-------------------------------------------------------------------*/

use std::default::*;
use std::fmt::*;

use crate::analysis_generic;    // identify source code
use analysis_generic::*;        // import public functions and types

/*---------------------------------------------------------
  - Declare Point<T, N> struct, like a C++ template class
  - Request compiler implement traits Debug & Clone
*/
#[derive(Debug, Clone)]
pub struct Point<T, const N: usize>
where
  T: Debug + Default + Clone
{
  coor: Vec<T>,
}
impl<T, const N: usize> Point<T, N>
where
T: Debug + Default + Clone
{
  /*-- constructor --*/
  pub fn new() -> Point<T, N> {
    Point::<T, N> {
      coor: vec![T::default(); N],
    }
  }
  /*-------------------------------------------------------
    Point<T, N>::init(&self, v:Vec<T>) fills coor with
    first N values from v and sets any remainder to
    T::default().
  -------------------------------------------------------*/
  pub fn init(mut self, coord: &Vec<T>) -> Point<T, N> {
    for i in 1..N {
      if i < coord.len() {
        self.coor[i] = coord[i].clone();
      }
      else {
        self.coor[i] = T::default();
      }
    }
    self
  }
  pub fn len(&self) -> usize {
    self.coor.len()
  }
  /*-- acts as both get_coor() and set_coor(some_vector) --*/
  pub fn coors(&mut self) -> &mut Vec<T> {
    &mut self.coor
  }
  /*-- displays name, type, and coordinates --*/
  pub fn show(&self, nm:&str, left: usize, width:usize) {
    println!("  {nm:?}: Point<T, N> {{");
    show_fold(&self.coor, left + 2, width);
    println!("  }}")
  }
}
/*-- implements const indexer -----------------*/
impl<T:Debug, const N:usize, Idx> std::ops::Index<Idx> for Point<T, N>
    where
        T:Debug + Default + Clone,
        Idx: std::slice::SliceIndex<[T]>
{
    type Output = Idx::Output;

    fn index(&self, index:Idx) -> &Self::Output {
        &self.coor[index]
    }
}
/*-- implements mutable indexer ---------------*/
impl<T, const N: usize, Idx> std::ops::IndexMut<Idx> for Point<T, N>
    where
        T:Debug + Default + Clone,
        Idx: std::slice::SliceIndex<[T]>
{
    fn index_mut(&mut self, index:Idx) -> &mut Self::Output {
        &mut self.coor[index]
    }
}
/* explicit conversion to slice &[T] */
impl<T, const N: usize> AsRef<[T]> for Point<T, N>
  where
    T: ?Sized,
    T: Debug + Display + Default + Clone,
{
  fn as_ref(&self) -> &[T] {
    &self.coor
  }
}
/* implicit conversion to slice &[T] */
impl<T, const N: usize> std::ops::Deref for Point<T, N>
  where T: Debug + Default + Clone,
{
  type Target = [T];

  fn deref(&self) -> &Self::Target {
    &self.coor
  }
}

/*---------------------------------------------------------
  Demonstrate user-defined Point<T, N> type
*/
pub fn demo_pointn() {

  show_label("demo indexing with Point<132, 5>", 40);
  println!();

  show_op("Point<i32, 5>");
  println!();
  let mut p = Point::<i32, 5>::new()
         .init(&vec![1, 2, 3, 2, 1]);
  p.show("p", 2, 12);
  println!();
  show_op("*p.coors() = vec![1, 0, -1, 0, 1]");
  *p.coors() = vec![1, 0, -1, 0, 1];
  p.show("p", 2, 12);

  println!("\n  using immutable indexer:");
  println!("  value of p[0] is {}\n", p[0]);
  println!("  using mutable indexer:");
  show_op("p[0] = 3");
  p[0] = 3;
  p.show("p", 2, 12);
  show_op("p[1] = 4");
  p[1] = 4;
  p.show("p", 2, 12);

}

/*-------------------------------------------------------------------
  analysis_generics.rs
  - provides analysis and display functions for Generics demo.
  - a few of these require advanced generics code.
  - You don't need to know how these work to understand this
    demo.
  - We will come back to these functions in rust_iter.
-------------------------------------------------------------------*/

use std::fmt::*;

/*---------------------------------------------------------
  Show input's call name and type
  - doesn't consume input
  - show_type is generic function with Debug bound.
    Using format "{:?}" requires Debug.
*/
pub fn show_type<T:Debug>(_t: &T, nm: &str) {
  let typename = std::any::type_name::<T>();
  println!("call name: {nm:?}, type: {typename:?}");
}
/*---------------------------------------------------------
  show_indexer<T:Debug>(nm:&str, s:&[T])
  - accepts any collection that implements Deref to slice
  - that includes array [T;N], slice T[N], Vec<T>, PointN<T>
*/
#[allow(clippy::needless_range_loop)]
pub fn demo_indexer<T>(nm:&str, s:&[T])
  where T: Debug + Display
{
  print!("  {}", nm);
  let max = s.len();
  print!{"  [ {:?}", s[0]};
  /* 1..max is range iterator */
  for i in 1..max {
      print!(", {:?}", s[i]);
  }
  println!(" ]");
  /*---------------------------------------------
    The code above is not idiomatic Rust.
    Rust style prefers using iterators over indexing
    like this:
    for item in s.iter() {
      print!("{item} ");
    }
  */
}
/*---------------------------------------------------------
  build indent string with "left" spaces
*/
pub fn offset(left: usize) -> String {
  let mut accum = String::new();
  for _i in 0..left {
    accum += " ";
  }
  accum
}
/*---------------------------------------------------------
  find index of last occurance of chr in s
  - returns option in case chr is not found
  https://stackoverflow.com/questions/50101842/how-to-find-the-last-occurrence-of-a-char-in-a-string
*/
fn find_last_utf8(s: &str, chr: char) -> Option<usize> {
  s.chars().rev().position(|c| c== chr)
    .map(|rev_pos| s.chars().count() - rev_pos - 1)

    /*-- alternate implementation --*/
  // if let Some(rev_pos) =
  //   s.chars().rev().position(|c| c == chr) {
  //     Some(s.chars().count() - rev_pos - 1)
  // } else {
  //     None
  // }
}
/*---------------------------------------------------------
  fold an enumerable's elements into rows of w elements
  - indent by left spaces
  - does not consume t since passed as reference
  - returns string
  https://users.rust-lang.org/t/generic-code-over-iterators/10907/3
*/
pub fn fold<T, I:Debug>(
  t: &T, left: usize, width: usize
) -> String
    where for<'a> &'a T: IntoIterator<Item = &'a I>, T:Debug
{
  let mut accum = String::new();
  accum += &offset(left);

  for (i, item) in t.into_iter().enumerate() {
    accum += &format!("{item:?}, ");
    if ((i + 1) % width) == 0 && i != 0 {
        accum += "\n";
        accum += &offset(left);
    }
  }
  /*-- Alternate direct implementation --*/
  //let mut i = 0usize;
  // for item in t {
  //   accum += &format!("{item:?}, ");
  //   if ((i + 1) % width) == 0 && i != 0 {
  //       accum += "\n";
  //       accum += &offset(left);
  //   }
  //   i += 1;
  // }

  let opt = find_last_utf8(&accum, ',');
  if let Some(index) = opt {
    accum.truncate(index);
  }
  accum
}
/*---------------------------------------------------------
  show enumerables's elements as folded rows
  - width is number of elements in each row
  - left is indent from terminal left
*/
pub fn show_fold<T:Debug, I:Debug>(t:&T, left:usize, width:usize)
  where for<'a> &'a T: IntoIterator<Item = &'a I>
{
  println!("{}",fold(t, left, width));
}
/*------------------------------------------------------------
  show string wrapped with long dotted lines above and below
*/
pub fn show_label(note: &str, n:usize) {
  let line =
    std::iter::repeat('-').take(n).collect::<String>();
  print!("\n{line}\n");
  print!("  {note}");
  print!("\n{line}\n");
}
pub fn show_label_def(note:&str) {
  show_label(note, 50);
}
/*---------------------------------------------------------
  show string wrapped with dotted lines above and below
*/
pub fn show_note(note: &str) {
  print!("\n-------------------------\n");
  print!(" {note}");
  print!("\n-------------------------\n");
}
/*---------------------------------------------------------
  show string wrapped in short lines
*/
pub fn show_op(opt: &str) {
  println!("--- {opt} ---");
}
/*---------------------------------------------------------
  print newline
*/
pub fn nl() {
  println!();
}

fn demo_generic_functions() {
  show_note("demo_generic_functions");
  println!();

  show_op("show_type<T:Debug>(_t, \"name\")");
  println!();

  let v = vec![1, 2, 3];
  show_type(&v, "v");
  let m = HashMap::<&str, i32>::new();
  show_type(&m, "m");
  println!();

  show_op("demo_indexer");
  println!();
  demo_indexer("[i32; 3]", &[1, 2, 3]);
  demo_indexer("Vec<i32>", &v);
  let p = PointN::<f64>::new(3).init(vec![1.0, 2.0, -0.5]);
  demo_indexer("PointN<f64>", &p);
}

#![allow(dead_code)]
#![allow(clippy::approx_constant)]

mod analysis_generic;     // identify module source file
use analysis_generic::*;  // import public functions and types
mod hello_generic;
use hello_generic::*;
mod stats;
use stats::*;
mod points_generic;
use points_generic::*;

use std::{fmt::*, collections::HashMap};

/*------------------------------------------
definition of type Demo has been elided
(shown below)
------------------------------------------*/

fn demo_std_generic_types() {
  /* defs elided */
}
fn demo_user_defined_generic_types() {
  /* defs elided */
}
fn demo_generic_functions() {
  /* defs elided */
}

fn main() {

  show_label("generic functions and types", 50);

  demo_std_generic_types();
  demo_user_defined_generic_types();
  demo_generic_functions();

  print!("\n\n  That's all Folks!\n\n");
}