90 lines
2.4 KiB
Rust
90 lines
2.4 KiB
Rust
use super::*;
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/// An [HSTRING] builder that supports preallocating the `HSTRING` to avoid extra allocations and copies.
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///
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/// This is similar to the `WindowsPreallocateStringBuffer` function but implemented directly in Rust for efficiency.
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/// It is implemented as a separate type since [HSTRING] values are immutable.
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pub struct HStringBuilder(*mut HStringHeader);
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impl HStringBuilder {
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/// Creates a preallocated `HSTRING` value.
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pub fn new(len: usize) -> Result<Self> {
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let header = HStringHeader::alloc(len.try_into()?)?;
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if len > 0 {
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unsafe { core::ptr::write_bytes((*header).data, 0, len) };
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}
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Ok(Self(header))
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}
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/// Shortens the string by removing any trailing 0 characters.
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pub fn trim_end(&mut self) {
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if let Some(header) = self.as_header_mut() {
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while header.len > 0
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&& unsafe { header.data.offset(header.len as isize - 1).read() == 0 }
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{
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header.len -= 1;
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}
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if header.len == 0 {
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unsafe {
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HStringHeader::free(self.0);
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}
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self.0 = core::ptr::null_mut();
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}
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}
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}
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fn as_header(&self) -> Option<&HStringHeader> {
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unsafe { self.0.as_ref() }
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}
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fn as_header_mut(&mut self) -> Option<&mut HStringHeader> {
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unsafe { self.0.as_mut() }
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}
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}
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impl From<HStringBuilder> for HSTRING {
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fn from(value: HStringBuilder) -> Self {
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if let Some(header) = value.as_header() {
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unsafe { header.data.offset(header.len as isize).write(0) };
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let result = Self(value.0);
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core::mem::forget(value);
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result
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} else {
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Self::new()
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}
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}
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}
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impl core::ops::Deref for HStringBuilder {
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type Target = [u16];
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fn deref(&self) -> &[u16] {
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if let Some(header) = self.as_header() {
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unsafe { core::slice::from_raw_parts(header.data, header.len as usize) }
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} else {
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&[]
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}
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}
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}
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impl core::ops::DerefMut for HStringBuilder {
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fn deref_mut(&mut self) -> &mut [u16] {
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if let Some(header) = self.as_header() {
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unsafe { core::slice::from_raw_parts_mut(header.data, header.len as usize) }
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} else {
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&mut []
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}
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}
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}
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impl Drop for HStringBuilder {
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fn drop(&mut self) {
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unsafe {
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HStringHeader::free(self.0);
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}
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}
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}
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