1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174

#![no_std]
use core::{fmt, ops, str};
use tinyvec::SliceVec;

#[derive(Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
#[repr(transparent)]
pub struct SliceString<'a>(SliceVec<'a, u8>);

impl<'a> SliceString<'a> {
    pub fn new(buf: &'a mut [u8]) -> Self {
        Self(SliceVec::from_slice_len(buf, 0))
    }

    pub fn into_slicevec(self) -> SliceVec<'a, u8> {
        self.0
    }

    pub unsafe fn as_mut_slicevec<'b: 'a>(&'b mut self) -> &'a mut SliceVec<'b, u8> {
        &mut self.0
    }

    pub fn as_str(&self) -> &str {
        unsafe { str::from_utf8_unchecked(&self.0) }
    }

    pub fn as_mut_str(&mut self) -> &mut str {
        unsafe { str::from_utf8_unchecked_mut(&mut self.0) }
    }

    pub fn capacity(&self) -> usize {
        self.0.capacity()
    }

    pub fn clear(&mut self) {
        self.0.clear()
    }

    pub fn len(&self) -> usize {
        self.0.len()
    }

    pub fn push_str(&mut self, string: &str) -> Result<(), ()> {
        let bytes = string.as_bytes();
        if self.capacity() < self.len() + bytes.len() {
            return Err(());
        }
        Ok(self.0.extend_from_slice(bytes))
    }

    pub fn pop(&mut self) -> Option<char> {
        let ch = self.chars().rev().next()?;
        self.0.truncate(self.len() - ch.len_utf8());
        Some(ch)
    }

    pub fn push(&mut self, c: char) -> Result<(), ()> {
        let len = c.len_utf8();
        if self.capacity() < self.len() + len {
            return Err(());
        }
        if len == 1 {
            Ok(self.0.push(c as u8))
        } else {
            Ok(self
                .0
                .extend_from_slice(c.encode_utf8(&mut [0; 4]).as_bytes()))
        }
    }

    pub fn truncate(&mut self, new_len: usize) {
        if new_len <= self.len() {
            assert!(self.is_char_boundary(new_len));
            self.0.truncate(new_len);
        }
    }
}

impl<'a> ops::Deref for SliceString<'a> {
    type Target = str;

    fn deref(&self) -> &str {
        self.as_str()
    }
}

impl<'a> ops::DerefMut for SliceString<'a> {
    fn deref_mut(&mut self) -> &mut str {
        self.as_mut_str()
    }
}

impl<'a> fmt::Display for SliceString<'a> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        <str as fmt::Display>::fmt(self, f)
    }
}

impl<'a> fmt::Write for SliceString<'a> {
    fn write_str(&mut self, s: &str) -> Result<(), fmt::Error> {
        self.push_str(s).map_err(|_| fmt::Error)
    }

    fn write_char(&mut self, c: char) -> Result<(), fmt::Error> {
        self.push(c).map_err(|_| fmt::Error)
    }
}

impl<'a> AsRef<str> for SliceString<'a> {
    fn as_ref(&self) -> &str {
        self
    }
}

impl<'a> AsRef<[u8]> for SliceString<'a> {
    fn as_ref(&self) -> &[u8] {
        self.as_bytes()
    }
}

// SliceString<'a> == str
impl<'a> PartialEq<str> for SliceString<'a> {
    fn eq(&self, other: &str) -> bool {
        str::eq(&self[..], &other[..])
    }
    fn ne(&self, other: &str) -> bool {
        str::ne(&self[..], &other[..])
    }
}

// SliceString<'a> == &'str
impl<'a> PartialEq<&str> for SliceString<'a> {
    fn eq(&self, other: &&str) -> bool {
        str::eq(&self[..], &other[..])
    }
    fn ne(&self, other: &&str) -> bool {
        str::ne(&self[..], &other[..])
    }
}

// str == SliceString<'a>
impl<'a> PartialEq<SliceString<'a>> for str {
    fn eq(&self, other: &SliceString<'a>) -> bool {
        str::eq(&self[..], &other[..])
    }
    fn ne(&self, other: &SliceString<'a>) -> bool {
        str::ne(&self[..], &other[..])
    }
}

// &'str == SliceString<'a>
impl<'a> PartialEq<SliceString<'a>> for &str {
    fn eq(&self, other: &SliceString<'a>) -> bool {
        str::eq(&self[..], &other[..])
    }
    fn ne(&self, other: &SliceString<'a>) -> bool {
        str::ne(&self[..], &other[..])
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn new() {
        let mut buf = [0u8; 32];
        let mut s = SliceString::new(&mut buf[..]);
        assert_eq!(0, s.len());
        s.push_str("Hello world!").unwrap();
        assert_eq!(s.as_str(), "Hello world!");

        let _r = unsafe { s.as_mut_slicevec() };
    }
}