fixedstr_ext/

tiny_internal.rs

//! This module is intended for internal use only.  Only a few
//! type aliases are exported.  A tiny string or `tstr<N>`, with N<=256,
//! is a version of fixed str that represents the best compromise between
//! memory and runtime efficiency.  Each `tstr<N>` can hold a string of up to
//! N-1 bytes, with max N=256.  A `tstr<N>` is represented underneath
//! by a `[u8;N]` with the first byte always representing the length of the
//! string.  A tstr is not necessarily zero-terminated.
//! Because currently Rust does not allow conditions on const generics
//! such as `where N<=256`, this type is not fully exported and one can
//! only use the type aliases.

#![allow(unused_variables)]
#![allow(non_snake_case)]
#![allow(non_camel_case_types)]
#![allow(unused_parens)]
#![allow(unused_assignments)]
#![allow(unused_mut)]
#![allow(unused_imports)]
#![allow(dead_code)]

#[cfg(not(feature = "no-alloc"))]
extern crate alloc;

#[cfg(feature = "std")]
#[cfg(not(feature = "no-alloc"))]
extern crate std;

#[cfg(feature = "std")]
#[cfg(not(feature = "no-alloc"))]
use crate::fstr;

use crate::zstr;
use crate::{str12, str128, str16, str192, str24, str256, str32, str4, str48, str64, str8, str96};
use core::cmp::{min, Ordering};
use core::ops::{Add, Index, IndexMut, Range, RangeFrom, RangeFull, RangeTo};
use core::ops::{RangeInclusive, RangeToInclusive};

/// **This structure is normally only accessible through the
/// public types [str4] through [str256].**  These types alias internal
/// types [tstr]\<4\> through [tstr]\<256\> respectively.  The purpose here
/// is to guarantee that the maximum size of the structure does not exceed
/// 256 bytes for it uses the first byte of a u8 array to hold the length of
/// the string.  The tstr type can be made directly public with the
/// **`pub-tstr` option**.
///
/// A feature unique to the tstr type aliases is the ability to concatenate
/// strings by generating higher-capacity types. Concatenating two strN
/// strings will always generate a strM with M=2*N, for str4 - str128.
/// ```
///   # use fixedstr_ext::*;
///   let a = str8::from("aaaaaa");
///   let b = str8::from("bbbbbb");
///   let c = a + b;  // type of c will be str16
///   assert_eq!(c,"aaaaaabbbbbb");
///   assert_eq!(c.capacity(), 15);
/// ```
/// In contrast, concatenating other string types such as zstr will always
/// produce strings of the same type and capacity.
#[derive(Copy, Clone, Eq)]
pub struct tstr<const N: usize = 256> {
    chrs: [u8; N],
} //tstr
impl<const N: usize> tstr<N> {
    /// creates a new `tstr<N>` with given &str.  If the length of s exceeds
    /// N, the extra characters are ignored.  This function is also called by
    /// several others including [tstr::from].  This function can now handle
    /// utf8 strings properly.
    pub fn make(s: &str) -> tstr<N> {
        let mut chars = [0u8; N];
        let bytes = s.as_bytes(); // &[u8]
        let blen = bytes.len();
        let limit = min(N - 1, blen);
        chars[1..limit + 1].copy_from_slice(&bytes[..limit]);
        chars[0] = limit as u8;
        //if chars[0] == 0 {
        //    chars[0] = blen as u8;
        //}
        tstr { chrs: chars }
    } //make

    /// alias for [Self::make]
    pub fn create(s: &str) -> tstr<N> {
        let mut chars = [0u8; N];
        let bytes = s.as_bytes();
        let blen = bytes.len();
        let limit = min(N - 1, blen);
        chars[1..limit + 1].copy_from_slice(&bytes[..limit]);
        chars[0] = limit as u8;
        //if chars[0] == 0 {
        //    chars[0] = blen as u8;
        //}
        tstr { chrs: chars }
    } //create

    /// version of make that returns the original string slice in an `Err(_)` if
    /// truncation is requried, or in an `Ok(_)` if no truncation is required
    pub fn try_make(s: &str) -> Result<tstr<N>, &str> {
        if s.len() + 1 > N {
            Err(s)
        } else {
            Ok(tstr::make(s))
        }
    }

    /// const constructor, to be called from const contexts.  However, as
    /// const functions are restricted from using iterators, it's slightly
    /// better to call the non-const constructors in non-const contexts.
    /// Truncates automatically.
    pub const fn const_make(s: &str) -> tstr<N> {
        let mut t = tstr::<N>::new();
        let mut len = s.len();
        if len > N - 1 {
            len = N - 1;
        } // fix max length
        t.chrs[0] = len as u8;
        let bytes = s.as_bytes();
        let mut i = 0;
        while i < len {
            t.chrs[i + 1] = bytes[i];
            i += 1;
        }
        t
    } //const_make

    /// Version of `const_make` that does not truncate.
    /// Additionally, because this operation is meant to be evaluated at
    /// compile time, N is checked to be at least 1 and at most 256: `None`
    /// is returned if conditions are violated.
    pub const fn const_try_make(s: &str) -> Option<tstr<N>> {
        if N == 0 || N > 256 || s.len() + 1 > N {
            None
        } else {
            Some(tstr::const_make(s))
        }
    }

    /// creates an empty string; equivalent to tstr::default() but can
    /// also be called from a const context.
    #[inline]
    pub const fn new() -> tstr<N> {
        tstr { chrs: [0; N] }
    }

    /// length of the string in bytes (consistent with [str::len]). This
    /// is a constant-time operation.
    #[inline]
    pub const fn len(&self) -> usize {
        self.chrs[0] as usize
    }

    /// returns the number of characters in the string regardless of
    /// character class.  This is not necessarily a constant-time operation.
    pub fn charlen(&self) -> usize {
        self.to_str().chars().count()
    }

    /// returns maximum capacity in bytes
    #[inline]
    pub const fn capacity(&self) -> usize {
        N - 1
    }

    /// converts tstr to an alloc::string::string
    #[cfg(not(feature = "no-alloc"))]
    pub fn to_string(&self) -> alloc::string::String {
        alloc::string::String::from(self.to_str())
    }

    /// returns slice of u8 the array underneath the tstr
    pub fn as_bytes(&self) -> &[u8] {
        &self.chrs[1..self.len() + 1]
    }

    /// returns mutable slice of the u8 array underneath (use with care)
    pub fn as_bytes_mut(&mut self) -> &mut [u8] {
        let n = self.len() + 1;
        &mut self.chrs[1..n]
    }

    /// converts tstr to &str using [core::str::from_utf8_unchecked]
    pub fn to_str(&self) -> &str {
        unsafe { core::str::from_utf8_unchecked(&self.chrs[1..self.len() + 1]) }
    }
    /// checked version of [tstr::to_str], but may panic
    pub fn as_str(&self) -> &str {
        core::str::from_utf8(&self.chrs[1..self.len() + 1]).unwrap()
    }
    /// version of [tstr::as_str] that does not call `unwrap`
    pub fn as_str_safe(&self) -> Result<&str, core::str::Utf8Error> {
        core::str::from_utf8(&self.chrs[1..self.len() + 1])
    }

    /// changes a character at *character position* i to c.  This function
    /// requires that c is in the same character class (ascii or unicode)
    /// as the char being replaced.  It never shuffles the bytes underneath.
    /// The function returns true if the change was successful.
    pub fn set(&mut self, i: usize, c: char) -> bool {
        let ref mut cbuf = [0u8; 4];
        c.encode_utf8(cbuf);
        let clen = c.len_utf8();
        if let Some((bi, rc)) = self.to_str().char_indices().nth(i) {
            if clen == rc.len_utf8() {
                self.chrs[bi + 1..bi + clen + 1].copy_from_slice(&cbuf[..clen]);
                //for k in 0..clen {self.chrs[bi+k+1] = cbuf[k];}
                return true;
            }
        }
        return false;
    } //set

    /// adds chars to end of current string up to maximum size N of `tstr<N>`,
    /// returns the portion of the push string that was NOT pushed due to
    /// capacity, so
    /// if "" is returned then all characters were pushed successfully.
    pub fn push<'t>(&mut self, s: &'t str) -> &'t str {
        self.push_str(s)
    } //push

    /// alias for [Self::push]
    pub fn push_str<'t>(&mut self, src: &'t str) -> &'t str {
        //self.push(s)
        let srclen = src.len();
        let slen = self.len();
        let bytes = &src.as_bytes();
        let length = core::cmp::min(slen + srclen, N - 1);
        let remain = if N - 1 >= (slen + srclen) {
            0
        } else {
            (srclen + slen) - N + 1
        };
        let mut i = 0;
        while i < srclen && i + slen + 1 < N {
            self.chrs[slen + i + 1] = bytes[i];
            i += 1;
        } //while
        self.chrs[0] += i as u8;
        &src[srclen - remain..]
    } //push_str

    /// pushes a single character to the end of the string, returning
    /// true on success.
    pub fn push_char(&mut self, c: char) -> bool {
        let clen = c.len_utf8();
        let slen = self.len();
        if slen + clen >= N {
            return false;
        }
        let mut buf = [0u8; 4]; // char buffer
        c.encode_utf8(&mut buf);
        for i in 0..clen {
            self.chrs[slen + i + 1] = buf[i];
        }
        self.chrs[0] = (slen + clen) as u8;
        true
    } // push_char

    /// remove and return last character in string, if it exists
    pub fn pop_char(&mut self) -> Option<char> {
        if self.len() == 0 {
            return None;
        }
        let (ci, lastchar) = self.char_indices().last().unwrap();
        self.chrs[0] = ci as u8;
        Some(lastchar)
    } //pop

    /// returns the nth char of the tstr
    pub fn nth(&self, n: usize) -> Option<char> {
        self.to_str().chars().nth(n)
    }

    /// returns the nth byte of the string as a char.  This
    /// function should only be called, for example, on ascii strings.  It
    /// is designed to be quicker than [tstr::nth], and does not check array bounds or
    /// check n against the length of the string. Nor does it check
    /// if the value returned is a valid character.
    pub const fn nth_bytechar(&self, n: usize) -> char {
        self.chrs[n + 1] as char
    }

    /// alias for [Self::nth_bytechar] (for backwards compatibility)
    pub const fn nth_ascii(&self, n: usize) -> char {
        self.chrs[n + 1] as char
    }

    /// determines if string is an ascii string
    pub fn is_ascii(&self) -> bool {
        self.to_str().is_ascii()
    }

    /// shortens the tstr in-place (mutates).  n indicates the number of
    /// *characters* to keep in thestring. If n is greater than the
    /// current character-length ([Self::charlen]) of the string, this operation will have no effect.
    pub fn truncate(&mut self, n: usize) // n is char position, not binary position
    {
        if let Some((bi, c)) = self.to_str().char_indices().nth(n) {
            self.chrs[0] = bi as u8;
        }
    }

    /// truncates string up to *byte* position n.  **Panics** if n is
    /// not on a character boundary, similar to truncate on owned Strings.
    pub fn truncate_bytes(&mut self, n: usize) {
        if (n < self.chrs[0] as usize) {
            assert!(self.is_char_boundary(n));
            self.chrs[0] = n as u8;
        }
    }

    /// Trims **in-place** trailing ascii whitespaces.  This function
    /// regards all bytes as single chars.  The operation panics if
    /// the resulting string does not end on a character boundary.
    pub fn right_ascii_trim(&mut self) {
        let mut n = self.chrs[0] as usize;
        while n > 0 && (self.chrs[n] as char).is_ascii_whitespace() {
            //self.chrs[n-1] = 0;
            n -= 1;
        }
        assert!(self.is_char_boundary(n));
        self.chrs[0] = n as u8;
    } //right_trim

    /// resets string to empty string
    pub fn clear(&mut self) {
        self.chrs[0] = 0;
    }

    /// in-place modification of ascii characters to lower-case. Panics if
    /// the string is not ascii.
    pub fn make_ascii_lowercase(&mut self) {
        assert!(self.is_ascii());
        let end = (self.chrs[0] as usize) + 1;
        for b in &mut self.chrs[1..end] {
            if *b >= 65 && *b <= 90 {
                *b |= 32;
            }
        }
    } //make_ascii_lowercase

    /// in-place modification of ascii characters to upper-case.  Panics if
    /// the string is not ascii.
    pub fn make_ascii_uppercase(&mut self) {
        assert!(self.is_ascii());
        let end = (self.chrs[0] as usize) + 1;
        for b in &mut self.chrs[1..end] {
            if *b >= 97 && *b <= 122 {
                *b -= 32;
            }
        }
    }

    /// Constructs a clone of this fstr but with only upper-case ascii
    /// characters.  This contrasts with [str::to_ascii_uppercase],
    /// which creates an owned String.
    pub fn to_ascii_upper(&self) -> Self {
        let mut cp = self.clone();
        cp.make_ascii_uppercase();
        cp
    }

    /// Constructs a clone of this fstr but with only lower-case ascii
    /// characters.  This contrasts with [str::to_ascii_lowercase],
    /// which creates an owned String.
    pub fn to_ascii_lower(&self) -> Self {
        let mut cp = *self;
        cp.make_ascii_lowercase();
        cp
    }

    /// Tests for ascii case-insensitive equality with another string.
    /// This function does not check if either string is ascii.
    pub fn case_insensitive_eq<TA>(&self, other: TA) -> bool
    where
        TA: AsRef<str>,
    {
        if self.len() != other.as_ref().len() {
            return false;
        }
        let obytes = other.as_ref().as_bytes();
        for i in 0..self.len() {
            let mut c = self.chrs[i + 1];
            if (c > 64 && c < 91) {
                c = c | 32;
            } // make lowercase
            let mut d = obytes[i];
            if (d > 64 && d < 91) {
                d = d | 32;
            } // make lowercase
            if c != d {
                return false;
            }
        } //for
        true
    } //case_insensitive_eq

    /// Decodes a UTF-16 encodeded slice. If a decoding error is encountered
    /// or capacity exceeded, an `Err(s)` is returned where s is the
    /// the encoded string up to the point of the error.
    pub fn from_utf16(v: &[u16]) -> Result<Self, Self> {
        let mut s = Self::new();
        for c in char::decode_utf16(v.iter().cloned()) {
            if let Ok(c1) = c {
                if !s.push_char(c1) {
                    return Err(s);
                }
            } else {
                return Err(s);
            }
        }
        Ok(s)
    } //from_utf16

    /*
       // These functions will replace calls to to_str (internal)
       // ... but both are unsafe because of unwrap
       #[cfg(not(feature = "prioritize-safety"))]
       #[inline(always)]
       fn makestr(&self) -> &str {
         unsafe { core::str::from_utf8_unchecked(&self.chrs[1..self.len() + 1]) }
      }
       #[cfg(feature = "prioritize-safety")]
       #[inline(always)]
       fn makestr(&self) -> &str {
         core::str::from_utf8(&self.chrs[1..self.len() + 1]).unwrap()
       }
    */
} //impl tstr<N>
  ///////////////////////

impl<const N: usize> core::ops::Deref for tstr<N> {
    type Target = str;
    fn deref(&self) -> &Self::Target {
        self.to_str()
    }
}

impl<const N: usize> core::convert::AsRef<str> for tstr<N> {
    fn as_ref(&self) -> &str {
        self.to_str()
    }
}
impl<const N: usize> core::convert::AsMut<str> for tstr<N> {
    fn as_mut(&mut self) -> &mut str {
        let blen = self.len() + 1;
        unsafe { core::str::from_utf8_unchecked_mut(&mut self.chrs[1..blen]) }
    }
}
impl<T: AsRef<str> + ?Sized, const N: usize> core::convert::From<&T> for tstr<N> {
    fn from(s: &T) -> tstr<N> {
        tstr::make(s.as_ref())
    }
}
impl<T: AsMut<str> + ?Sized, const N: usize> core::convert::From<&mut T> for tstr<N> {
    fn from(s: &mut T) -> tstr<N> {
        tstr::make(s.as_mut())
    }
}

#[cfg(not(feature = "no-alloc"))]
impl<const N: usize> core::convert::From<alloc::string::String> for tstr<N> {
    fn from(s: alloc::string::String) -> tstr<N> {
        tstr::<N>::make(&s[..])
    }
}

#[cfg(feature = "std")]
#[cfg(not(feature = "no-alloc"))]
impl<const N: usize, const M: usize> std::convert::From<fstr<M>> for tstr<N> {
    fn from(s: fstr<M>) -> tstr<N> {
        tstr::<N>::make(s.to_str())
    }
}

impl<const N: usize, const M: usize> core::convert::From<zstr<M>> for tstr<N> {
    fn from(s: zstr<M>) -> tstr<N> {
        tstr::<N>::make(s.to_str())
    }
}

impl<const N: usize> core::cmp::PartialOrd for tstr<N> {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl<const N: usize> core::cmp::Ord for tstr<N> {
    fn cmp(&self, other: &Self) -> Ordering {
        self.chrs[1..self.len() + 1].cmp(&other.chrs[1..other.len() + 1])
    }
}

impl<const M: usize> tstr<M> {
    /// converts an tstr\<M\> to an tstr\<N\>. If the length of the string being
    /// converted is greater than N-1, the extra characters will be ignored.
    /// This operation produces a copy (non-destructive).
    /// Example:
    ///```ignore
    ///  let s1:tstr<8> = tstr::from("abcdefg");
    ///  let s2:tstr<16> = s1.resize();
    ///```
    pub fn resize<const N: usize>(&self) -> tstr<N> {
        let slen = self.len();
        let length = if (slen < N - 1) { slen } else { N - 1 };
        let mut chars = [0u8; N];
        chars[1..length + 1].copy_from_slice(&self.chrs[1..length + 1]);
        //for i in 0..length {chars[i+1] = self.chrs[i+1];}
        chars[0] = (length) as u8;
        tstr { chrs: chars }
    } //resize

    /// version of resize that does not allow string truncation due to length
    pub fn reallocate<const N: usize>(&self) -> Option<tstr<N>> {
        if self.len() < N {
            Some(self.resize())
        } else {
            None
        }
    } //reallocate
} //impl tstr<M>

impl<const N: usize> core::fmt::Display for tstr<N> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        //write!(f, "{}", self.to_str())
        f.pad(self.to_str())
    }
}

impl<const N: usize> PartialEq<&str> for tstr<N> {
    fn eq(&self, other: &&str) -> bool {
        self.to_str() == *other // see below
    } //eq
}
impl<const N: usize> PartialEq<&str> for &tstr<N> {
    fn eq(&self, other: &&str) -> bool {
        &self.to_str() == other
    } //eq
}
impl<'t, const N: usize> PartialEq<tstr<N>> for &'t str {
    fn eq(&self, other: &tstr<N>) -> bool {
        &other.to_str() == self
    }
}
impl<'t, const N: usize> PartialEq<&tstr<N>> for &'t str {
    fn eq(&self, other: &&tstr<N>) -> bool {
        &other.to_str() == self
    }
}

/// defaults to empty string
impl<const N: usize> Default for tstr<N> {
    fn default() -> Self {
        tstr::<N>::new()
    }
}
#[cfg(feature = "std")]
#[cfg(not(feature = "no-alloc"))]
impl<const N: usize, const M: usize> PartialEq<tstr<N>> for fstr<M> {
    fn eq(&self, other: &tstr<N>) -> bool {
        other.to_str() == self.to_str()
    }
}
#[cfg(feature = "std")]
#[cfg(not(feature = "no-alloc"))]
impl<const N: usize, const M: usize> PartialEq<fstr<N>> for tstr<M> {
    fn eq(&self, other: &fstr<N>) -> bool {
        other.to_str() == self.to_str()
    }
}

impl<const N: usize, const M: usize> PartialEq<zstr<N>> for tstr<M> {
    fn eq(&self, other: &zstr<N>) -> bool {
        other.to_str() == self.to_str()
    }
}

impl<const N: usize> core::fmt::Debug for tstr<N> {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.pad(&self.to_str())
    }
} // Debug impl

/*
///Convert tstr to &str slice
impl<IndexType, const N: usize> core::ops::Index<IndexType> for tstr<N>
where
    IndexType: core::slice::SliceIndex<str>,
{
    type Output = IndexType::Output;
    fn index(&self, index: IndexType) -> &Self::Output {
        &self.to_str()[index]
    }
} //impl Index
*/

impl<const N: usize> tstr<N> {
    /// returns a copy of the portion of the string, string could be truncated
    /// if indices are out of range. Similar to slice [start..end]
    pub fn substr(&self, start: usize, end: usize) -> tstr<N> {
        let mut chars = [0u8; N];
        let mut inds = self.char_indices();
        let len = self.len();
        if start >= len || end <= start {
            return tstr { chrs: chars };
        }
        chars[0] = (end - start) as u8;
        let (si, _) = inds.nth(start).unwrap();
        let last = if (end >= len) {
            len
        } else {
            match inds.nth(end - start - 1) {
                Some((ei, _)) => ei,
                None => len,
            } //match
        }; //let last =...
        chars[1..last - si + 1].copy_from_slice(&self.chrs[si + 1..last + 1]);
        /*
        for i in si..last
        {
          chars[i-si+1] = self.chrs[i+1];
        }
        */
        tstr { chrs: chars }
    } //substr
}

impl Add for str8 {
    type Output = str16;
    fn add(self, other: Self) -> Self::Output {
        let mut cat: Self::Output = self.resize();
        let slen = self.len();
        let olen = other.len();
        cat.chrs[slen + 1..slen + olen + 1].copy_from_slice(&other.chrs[1..olen + 1]);
        cat.chrs[0] = (slen + olen) as u8;
        cat
    }
} //Add

impl Add for str16 {
    type Output = str32;
    fn add(self, other: Self) -> Self::Output {
        let mut cat: Self::Output = self.resize();
        let slen = self.len();
        let olen = other.len();
        cat.chrs[slen + 1..slen + olen + 1].copy_from_slice(&other.chrs[1..olen + 1]);
        cat.chrs[0] = (slen + olen) as u8;
        cat
    }
} //Add

impl Add for str32 {
    type Output = str64;
    fn add(self, other: Self) -> Self::Output {
        let mut cat: Self::Output = self.resize();
        let slen = self.len();
        let olen = other.len();
        cat.chrs[slen + 1..slen + olen + 1].copy_from_slice(&other.chrs[1..olen + 1]);
        cat.chrs[0] = (slen + olen) as u8;
        cat
    }
} //Add

impl Add for str64 {
    type Output = str128;
    fn add(self, other: Self) -> Self::Output {
        let mut cat: Self::Output = self.resize();
        let slen = self.len();
        let olen = other.len();
        cat.chrs[slen + 1..slen + olen + 1].copy_from_slice(&other.chrs[1..olen + 1]);
        cat.chrs[0] = (slen + olen) as u8;
        cat
    }
} //Add

impl Add for str128 {
    type Output = str256;
    fn add(self, other: Self) -> Self::Output {
        let mut cat: Self::Output = self.resize();
        let slen = self.len();
        let olen = other.len();
        cat.chrs[slen + 1..slen + olen + 1].copy_from_slice(&other.chrs[1..olen + 1]);
        cat.chrs[0] = (slen + olen) as u8;
        cat
    }
} //Add

impl Add for str4 {
    type Output = str8;
    fn add(self, other: Self) -> Self::Output {
        let mut cat: Self::Output = self.resize();
        let slen = self.len();
        let olen = other.len();
        cat.chrs[slen + 1..slen + olen + 1].copy_from_slice(&other.chrs[1..olen + 1]);
        cat.chrs[0] = (slen + olen) as u8;
        cat
    }
} //Add

impl Add for str12 {
    type Output = str24;
    fn add(self, other: Self) -> Self::Output {
        let mut cat: Self::Output = self.resize();
        let slen = self.len();
        let olen = other.len();
        cat.chrs[slen + 1..slen + olen + 1].copy_from_slice(&other.chrs[1..olen + 1]);
        cat.chrs[0] = (slen + olen) as u8;
        cat
    }
} //Add

impl Add for str24 {
    type Output = str48;
    fn add(self, other: Self) -> Self::Output {
        let mut cat: Self::Output = self.resize();
        let slen = self.len();
        let olen = other.len();
        cat.chrs[slen + 1..slen + olen + 1].copy_from_slice(&other.chrs[1..olen + 1]);
        cat.chrs[0] = (slen + olen) as u8;
        cat
    }
} //Add

impl Add for str48 {
    type Output = str96;
    fn add(self, other: Self) -> Self::Output {
        let mut cat: Self::Output = self.resize();
        let slen = self.len();
        let olen = other.len();
        cat.chrs[slen + 1..slen + olen + 1].copy_from_slice(&other.chrs[1..olen + 1]);
        cat.chrs[0] = (slen + olen) as u8;
        cat
    }
} //Add

impl Add for str96 {
    type Output = str192;
    fn add(self, other: Self) -> Self::Output {
        let mut cat: Self::Output = self.resize();
        let slen = self.len();
        let olen = other.len();
        cat.chrs[slen + 1..slen + olen + 1].copy_from_slice(&other.chrs[1..olen + 1]);
        cat.chrs[0] = (slen + olen) as u8;
        cat
    }
} //Add

/* conflicting impl
impl<const N: usize,TA:AsRef<str>> Add<TA> for tstr<N> {
    type Output = tstr<N>;
    fn add(self, other: TA) -> tstr<N> {
        let mut a2 = self;
        a2.push(other.as_ref());
        a2
    }
} //Add &str
*/

impl<const N: usize> Add<&str> for tstr<N> {
    type Output = tstr<N>;
    fn add(self, other: &str) -> tstr<N> {
        let mut a2 = self;
        a2.push(other);
        a2
    }
} //Add &str

impl<const N: usize> Add<&tstr<N>> for &str {
    type Output = tstr<N>;
    fn add(self, other: &tstr<N>) -> tstr<N> {
        let mut a2 = tstr::from(self);
        a2.push(other);
        a2
    }
} //Add &str on left

impl<const N: usize> Add<tstr<N>> for &str {
    type Output = tstr<N>;
    fn add(self, other: tstr<N>) -> tstr<N> {
        let mut a2 = tstr::from(self);
        a2.push(&other);
        a2
    }
} //Add &str on left

////////////// core::fmt::Write trait
/// Usage:
/// ```
///   # use fixedstr_ext::*;
///   use core::fmt::Write;
///   let mut s = str16::new();
///   let result = write!(&mut s,"hello {}, {}, {}",1,2,3);
///   /* or */
///   let s2 = str_format!(str32,"abx{}{}{}",1,2,3);
/// ```
impl<const N: usize> core::fmt::Write for tstr<N> {
    fn write_str(&mut self, s: &str) -> core::fmt::Result {
        if s.len() + self.len() + 1 > N {
            return Err(core::fmt::Error::default());
        }
        self.push(s);
        Ok(())
    } //write_str
} //core::fmt::Write trait

impl<const N: usize> core::hash::Hash for tstr<N> {
    fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
        self.as_ref().hash(state);
    }
} //hash

impl<const N: usize> core::cmp::PartialEq for tstr<N> {
    fn eq(&self, other: &Self) -> bool {
        self.as_ref() == other.as_ref()
    }
}

impl<const N: usize> core::str::FromStr for tstr<N> {
    type Err = &'static str;
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if N < 257 && s.len() < N {
            Ok(tstr::from(s))
        } else {
            Err("Parse Error: capacity exceeded")
        }
    }
}

/// const function to limit usize value to between 1 and 256.
/// Can be called when tstr is created (under `pub-tstr` feature):
/// ```
///   #[cfg(feature = "pub-tstr")]
///   # use fixedstr_ext::*;
///   let ls = tstr::<{tstr_limit(258)}>::from("abcd");
///   assert_eq!(ls.capacity(),255);
/// ```
#[cfg(feature = "pub-tstr")]
pub const fn tstr_limit(n: usize) -> usize {
    if n == 0 {
        1
    } else if n > 256 {
        256
    } else {
        n
    }
} //const limit_size

/*   cannot adopt, because it affects type inference of s1 == s2.resize()
impl<const N: usize, const M:usize> core::cmp::PartialEq<tstr<M>> for tstr<N> {
    fn eq(&self, other: &tstr<M>) -> bool {
       self.as_ref() == other.as_ref()
    }
}
*/