write16/
lib.rs

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
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
// Copyright Mozilla Foundation
//
// Licensed under the Apache License (Version 2.0), or the MIT license,
// (the "Licenses") at your option. You may not use this file except in
// compliance with one of the Licenses. You may obtain copies of the
// Licenses at:
//
//    https://www.apache.org/licenses/LICENSE-2.0
//    https://opensource.org/licenses/MIT
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the Licenses is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the Licenses for the specific language governing permissions and
// limitations under the Licenses.

#![no_std]

//! `write16` provides the trait `Write16`, which a UTF-16 analog of the
//! `core::fmt::Write` trait (the sink part—not the formatting part).

#[cfg(feature = "alloc")]
extern crate alloc;
#[cfg(feature = "arrayvec")]
extern crate arrayvec;
#[cfg(feature = "smallvec")]
extern crate smallvec;

/// A UTF-16 sink analogous to `core::fmt::Write`.
pub trait Write16 {
    /// Write a slice containing UTF-16 to the sink.
    ///
    /// The implementor of the trait should not validate UTF-16.
    /// It's the responsibility of the caller to pass valid
    /// UTF-16.
    fn write_slice(&mut self, s: &[u16]) -> core::fmt::Result;

    /// Write a Unicode scalar value to the sink.
    #[inline(always)]
    fn write_char(&mut self, c: char) -> core::fmt::Result {
        let mut buf = [0u16; 2];
        self.write_slice(c.encode_utf16(&mut buf))
    }

    /// A hint that the caller expects to write `upcoming` UTF-16
    /// code units. The implementation must not assume `upcoming`
    /// to be exact. The caller may write more or fewer code units
    /// using `write_slice()` and `write_char()`. However, the
    /// caller should try to give reasonable estimates if it uses
    /// this method.
    ///
    /// For `Vec` and `SmallVec`, this maps to `reserve()`.
    /// The default implementation does nothing.
    #[inline(always)]
    fn size_hint(&mut self, upcoming: usize) -> core::fmt::Result {
        let _ = upcoming;
        Ok(())
    }
}

#[cfg(feature = "alloc")]
impl Write16 for alloc::vec::Vec<u16> {
    #[inline(always)]
    fn write_slice(&mut self, s: &[u16]) -> core::fmt::Result {
        self.extend_from_slice(s);
        Ok(())
    }

    #[inline(always)]
    fn write_char(&mut self, c: char) -> core::fmt::Result {
        if c <= '\u{FFFF}' {
            self.push(c as u16);
        } else {
            let mut buf = [0u16; 2];
            let u = u32::from(c);
            buf[0] = (0xD7C0 + (u >> 10)) as u16;
            buf[1] = (0xDC00 + (u & 0x3FF)) as u16;
            self.extend_from_slice(&mut buf);
        }
        Ok(())
    }

    #[inline(always)]
    fn size_hint(&mut self, upcoming: usize) -> core::fmt::Result {
        self.reserve(upcoming);
        Ok(())
    }
}

#[cfg(feature = "smallvec")]
impl<A: smallvec::Array<Item = u16>> Write16 for smallvec::SmallVec<A> {
    #[inline(always)]
    fn write_slice(&mut self, s: &[u16]) -> core::fmt::Result {
        self.extend_from_slice(s);
        Ok(())
    }

    #[inline(always)]
    fn write_char(&mut self, c: char) -> core::fmt::Result {
        if c <= '\u{FFFF}' {
            self.push(c as u16);
        } else {
            let mut buf = [0u16; 2];
            let u = u32::from(c);
            buf[0] = (0xD7C0 + (u >> 10)) as u16;
            buf[1] = (0xDC00 + (u & 0x3FF)) as u16;
            self.extend_from_slice(&mut buf);
        }
        Ok(())
    }

    #[inline(always)]
    fn size_hint(&mut self, upcoming: usize) -> core::fmt::Result {
        self.reserve(upcoming);
        Ok(())
    }
}

#[cfg(feature = "arrayvec")]
impl<const CAP: usize> Write16 for arrayvec::ArrayVec<u16, CAP> {
    #[inline(always)]
    fn write_slice(&mut self, s: &[u16]) -> core::fmt::Result {
        if self.try_extend_from_slice(s).is_ok() {
            Ok(())
        } else {
            Err(core::fmt::Error {})
        }
    }

    #[inline(always)]
    fn write_char(&mut self, c: char) -> core::fmt::Result {
        if c <= '\u{FFFF}' {
            if self.try_push(c as u16).is_ok() {
                Ok(())
            } else {
                Err(core::fmt::Error {})
            }
        } else {
            let mut buf = [0u16; 2];
            let u = u32::from(c);
            buf[0] = (0xD7C0 + (u >> 10)) as u16;
            buf[1] = (0xDC00 + (u & 0x3FF)) as u16;
            self.write_slice(&mut buf)
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::Write16;

    #[cfg(feature = "alloc")]
    #[test]
    fn test_vec() {
        let mut v: alloc::vec::Vec<u16> = alloc::vec::Vec::new();
        assert_eq!(v.capacity(), 0);
        assert!(v.size_hint(32).is_ok());
        assert!(v.capacity() >= 32);
        assert_eq!(v.len(), 0);
        assert!(v.write_slice([0x0061u16, 0x0062u16].as_slice()).is_ok());
        assert_eq!(v.len(), 2);
        assert!(v.write_char('☃').is_ok());
        assert_eq!(v.len(), 3);
        assert!(v.write_char('😊').is_ok());
        assert_eq!(v.len(), 5);
        assert_eq!(
            v.as_slice(),
            [0x0061u16, 0x0062u16, 0x2603u16, 0xD83Du16, 0xDE0Au16].as_slice()
        );
    }

    #[cfg(feature = "smallvec")]
    #[test]
    fn test_smallvec() {
        let mut v: smallvec::SmallVec<[u16; 2]> = smallvec::SmallVec::new();
        assert_eq!(v.capacity(), 2);
        assert!(v.size_hint(32).is_ok());
        assert!(v.capacity() >= 32);
        assert_eq!(v.len(), 0);
        assert!(v.write_slice([0x0061u16, 0x0062u16].as_slice()).is_ok());
        assert_eq!(v.len(), 2);
        assert!(v.write_char('☃').is_ok());
        assert_eq!(v.len(), 3);
        assert!(v.write_char('😊').is_ok());
        assert_eq!(v.len(), 5);
        assert_eq!(
            v.as_slice(),
            [0x0061u16, 0x0062u16, 0x2603u16, 0xD83Du16, 0xDE0Au16].as_slice()
        );
    }

    #[cfg(feature = "arrayvec")]
    #[test]
    fn test_arrayvec() {
        let mut v: arrayvec::ArrayVec<u16, 4> = arrayvec::ArrayVec::new();
        assert_eq!(v.capacity(), 4);
        assert!(v.size_hint(32).is_ok());
        assert_eq!(v.capacity(), 4);
        assert_eq!(v.len(), 0);
        assert!(v.write_char('😊').is_ok());
        assert_eq!(v.len(), 2);
        assert!(v.write_char('☃').is_ok());
        assert_eq!(v.len(), 3);
        assert!(v.write_char('😊').is_err());
        assert_eq!(v.len(), 3);
        assert_eq!(v.as_slice(), [0xD83Du16, 0xDE0Au16, 0x2603u16].as_slice());
    }
}