303 lines
7.1 KiB
Rust
303 lines
7.1 KiB
Rust
use std::alloc::{alloc, dealloc, handle_alloc_error, realloc, Layout};
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use std::fmt;
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use std::mem::{align_of, ManuallyDrop};
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use std::ops::{Add, AddAssign};
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use std::ptr;
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/// Buffer for rendered contents
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///
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/// This struct is quite simular to `String`, but some methods are
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/// re-implemented for faster buffering.
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pub struct Buffer {
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data: *mut u8,
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len: usize,
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capacity: usize,
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}
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impl Buffer {
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#[inline]
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pub const fn new() -> Buffer {
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Self {
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data: align_of::<u8>() as *mut u8, // dangling pointer
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len: 0,
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capacity: 0,
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}
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}
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#[inline]
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pub fn with_capacity(n: usize) -> Buffer {
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unsafe {
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if n == 0 {
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Self::new()
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} else {
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let layout = Layout::from_size_align_unchecked(n, 1);
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let data = alloc(layout);
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if data.is_null() {
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handle_alloc_error(layout);
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}
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Self {
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data,
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len: 0,
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capacity: n,
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}
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}
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}
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}
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#[inline]
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pub fn as_str(&self) -> &str {
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unsafe {
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let bytes = std::slice::from_raw_parts(self.data, self.len);
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std::str::from_utf8_unchecked(bytes)
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}
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}
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#[inline]
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pub fn as_mut_ptr(&self) -> *mut u8 {
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self.data
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}
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#[inline]
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pub fn len(&self) -> usize {
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self.len
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}
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#[inline]
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pub fn capacity(&self) -> usize {
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self.capacity
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}
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/// Force the length of buffer to `new_len`
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///
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/// # Safety
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///
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/// - `new_len` must be less than or equal to `capacity()`
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/// - The elements at `old_len..new_len` must be initialized
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#[inline]
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pub unsafe fn set_len(&mut self, new_len: usize) {
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self.len = new_len;
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}
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#[inline]
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pub fn is_empty(&self) -> bool {
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self.len == 0
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}
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#[inline]
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pub fn reserve(&mut self, size: usize) {
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if size > self.capacity - self.len {
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self.reserve_internal(size);
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}
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}
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#[inline]
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pub fn clear(&mut self) {
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self.len = 0;
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}
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#[inline]
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pub fn into_string(self) -> String {
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let buf = ManuallyDrop::new(self);
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unsafe { String::from_raw_parts(buf.data, buf.len, buf.capacity) }
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}
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#[inline]
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pub fn push_str(&mut self, data: &str) {
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let size = data.len();
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if size > self.capacity - self.len {
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self.reserve_internal(size);
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}
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unsafe {
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let p = self.data.add(self.len);
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std::ptr::copy_nonoverlapping(data.as_ptr(), p, size);
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self.len += size;
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}
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}
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#[inline]
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pub fn push(&mut self, data: char) {
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let mut buf = [0u8; 4];
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self.push_str(data.encode_utf8(&mut buf));
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}
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#[inline(never)]
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fn reserve_internal(&mut self, size: usize) {
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unsafe {
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let new_capacity = std::cmp::max(self.capacity * 2, self.len + size);
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self.realloc(new_capacity);
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self.capacity = new_capacity;
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}
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}
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unsafe fn realloc(&mut self, cap: usize) {
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if self.capacity == 0 {
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let new_layout = Layout::from_size_align_unchecked(cap, 1);
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self.data = alloc(new_layout);
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} else {
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assert!(cap <= std::usize::MAX / 2, "capacity is too large");
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let old_layout = Layout::from_size_align_unchecked(self.capacity, 1);
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self.data = realloc(self.data, old_layout, cap);
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}
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if self.data.is_null() {
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handle_alloc_error(Layout::from_size_align_unchecked(cap, 1));
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}
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}
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}
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impl Clone for Buffer {
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fn clone(&self) -> Self {
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unsafe {
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if self.capacity == 0 {
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Self::new()
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} else {
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let layout = Layout::from_size_align_unchecked(self.len, 1);
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let data = alloc(layout);
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if data.is_null() {
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handle_alloc_error(layout);
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}
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let buf = Self {
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data,
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len: self.len,
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capacity: self.len,
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};
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ptr::copy_nonoverlapping(self.data, buf.data, self.len);
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buf
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}
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}
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}
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}
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impl fmt::Debug for Buffer {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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self.as_str().fmt(f)
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}
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}
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impl Drop for Buffer {
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fn drop(&mut self) {
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if self.capacity != 0 {
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unsafe {
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let layout = Layout::from_size_align_unchecked(self.capacity, 1);
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dealloc(self.data, layout);
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}
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}
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}
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}
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impl fmt::Write for Buffer {
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#[inline]
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fn write_str(&mut self, s: &str) -> fmt::Result {
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Buffer::push_str(self, s);
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Ok(())
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}
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}
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impl From<String> for Buffer {
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#[inline]
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fn from(other: String) -> Buffer {
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let mut other = ManuallyDrop::new(other);
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Buffer {
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data: other.as_mut_ptr(),
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len: other.len(),
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capacity: other.capacity(),
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}
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}
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}
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impl From<&str> for Buffer {
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#[inline]
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fn from(other: &str) -> Buffer {
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Buffer::from(other.to_owned())
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}
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}
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impl Add<&str> for Buffer {
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type Output = Buffer;
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#[inline]
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fn add(mut self, other: &str) -> Buffer {
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self.push_str(other);
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self
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}
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}
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impl AddAssign<&str> for Buffer {
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#[inline]
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fn add_assign(&mut self, other: &str) {
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self.push_str(other)
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}
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}
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impl Default for Buffer {
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#[inline]
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fn default() -> Buffer {
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Buffer::new()
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}
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}
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#[cfg(test)]
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mod tests {
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use super::Buffer;
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#[test]
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fn test1() {
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let mut buffer = Buffer::new();
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assert_eq!(buffer.len(), 0);
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assert_eq!(buffer.capacity(), 0);
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buffer.push_str("apple");
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assert_eq!(buffer.len(), 5);
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assert_eq!(buffer.capacity(), 5);
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buffer.push_str("pie");
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assert_eq!(buffer.len(), 8);
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assert_eq!(buffer.capacity(), 10);
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}
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#[test]
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fn test2() {
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let mut buffer = Buffer::with_capacity(1);
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assert!(buffer.is_empty());
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assert_eq!(buffer.len(), 0);
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assert!(buffer.capacity() >= 1);
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buffer += "pie";
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assert!(!buffer.is_empty());
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}
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#[test]
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fn string_conversion() {
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// from empty string
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let s = String::new();
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let mut buf = Buffer::from(s);
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assert_eq!(buf.as_str(), "");
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buf.push_str("abc");
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assert_eq!(buf.as_str(), "abc");
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// into non-empty string
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let mut s = buf.into_string();
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assert_eq!(s, "abc");
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s.push_str("defghijklmn");
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assert_eq!(s, "abcdefghijklmn");
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// from non-empty string
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let mut buf = Buffer::from(s);
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assert_eq!(buf.as_str(), "abcdefghijklmn");
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buf.clear();
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assert_eq!(buf.as_str(), "");
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// into empty string
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let buf = Buffer::new();
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let mut s = buf.into_string();
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assert_eq!(s, "");
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s.push_str("apple");
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assert_eq!(s, "apple");
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}
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}
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