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|
use super::*;
/// An [HSTRING] builder that supports preallocating the `HSTRING` to avoid extra allocations and copies.
///
/// This is similar to the `WindowsPreallocateStringBuffer` function but implemented directly in Rust for efficiency.
/// It is implemented as a separate type since [HSTRING] values are immutable.
pub struct HStringBuilder(*mut HStringHeader);
impl HStringBuilder {
/// Creates a preallocated `HSTRING` value.
pub fn new(len: usize) -> Self {
let header = HStringHeader::alloc(len.try_into().unwrap());
if len > 0 {
unsafe { core::ptr::write_bytes((*header).data, 0, len) };
}
Self(header)
}
/// Shortens the string by removing any trailing 0 characters.
pub fn trim_end(&mut self) {
if let Some(header) = self.as_header_mut() {
while header.len > 0
&& unsafe { header.data.offset(header.len as isize - 1).read() == 0 }
{
header.len -= 1;
}
if header.len == 0 {
unsafe {
HStringHeader::free(self.0);
}
self.0 = core::ptr::null_mut();
}
}
}
/// Allows the `HSTRING` to be constructed from bytes.
pub fn as_bytes_mut(&mut self) -> &mut [u8] {
if let Some(header) = self.as_header() {
unsafe {
core::slice::from_raw_parts_mut(header.data as *mut _, header.len as usize * 2)
}
} else {
&mut []
}
}
fn as_header(&self) -> Option<&HStringHeader> {
unsafe { self.0.as_ref() }
}
fn as_header_mut(&mut self) -> Option<&mut HStringHeader> {
unsafe { self.0.as_mut() }
}
}
impl From<HStringBuilder> for HSTRING {
fn from(value: HStringBuilder) -> Self {
if let Some(header) = value.as_header() {
unsafe { header.data.offset(header.len as isize).write(0) };
let result = Self(value.0);
core::mem::forget(value);
result
} else {
Self::new()
}
}
}
impl core::ops::Deref for HStringBuilder {
type Target = [u16];
fn deref(&self) -> &[u16] {
if let Some(header) = self.as_header() {
unsafe { core::slice::from_raw_parts(header.data, header.len as usize) }
} else {
&[]
}
}
}
impl core::ops::DerefMut for HStringBuilder {
fn deref_mut(&mut self) -> &mut [u16] {
if let Some(header) = self.as_header() {
unsafe { core::slice::from_raw_parts_mut(header.data, header.len as usize) }
} else {
&mut []
}
}
}
impl Drop for HStringBuilder {
fn drop(&mut self) {
unsafe {
HStringHeader::free(self.0);
}
}
}
|
