59 lines
2.1 KiB
Rust
59 lines
2.1 KiB
Rust
//! A helper module containing unsafe utility functions.
|
|
|
|
use crate::dynamic::Variant;
|
|
|
|
use crate::stdlib::{
|
|
any::{Any, TypeId},
|
|
boxed::Box,
|
|
mem, ptr,
|
|
};
|
|
|
|
/// Cast a type into another type.
|
|
#[inline(always)]
|
|
pub fn unsafe_try_cast<A: Any, B: Any>(a: A) -> Option<B> {
|
|
if TypeId::of::<B>() == a.type_id() {
|
|
// SAFETY: Just checked we have the right type. We explicitly forget the
|
|
// value immediately after moving out, removing any chance of a destructor
|
|
// running or value otherwise being used again.
|
|
unsafe {
|
|
let ret: B = ptr::read(&a as *const _ as *const B);
|
|
mem::forget(a);
|
|
Some(ret)
|
|
}
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
|
|
/// Cast a Boxed type into another type.
|
|
#[inline(always)]
|
|
pub fn unsafe_cast_box<X: Variant, T: Variant>(item: Box<X>) -> Result<Box<T>, Box<X>> {
|
|
// Only allow casting to the exact same type
|
|
if TypeId::of::<X>() == TypeId::of::<T>() {
|
|
// SAFETY: just checked whether we are pointing to the correct type
|
|
unsafe {
|
|
let raw: *mut dyn Any = Box::into_raw(item as Box<dyn Any>);
|
|
Ok(Box::from_raw(raw as *mut T))
|
|
}
|
|
} else {
|
|
// Return the consumed item for chaining.
|
|
Err(item)
|
|
}
|
|
}
|
|
|
|
/// # DANGEROUS!!!
|
|
///
|
|
/// A dangerous function that blindly casts a `&str` from one lifetime to a `&str` of
|
|
/// another lifetime. This is mainly used to let us push a block-local variable into the
|
|
/// current `Scope` without cloning the variable name. Doing this is safe because all local
|
|
/// variables in the `Scope` are cleared out before existing the block.
|
|
///
|
|
/// Force-casting a local variable's lifetime to the current `Scope`'s larger lifetime saves
|
|
/// on allocations and string cloning, thus avoids us having to maintain a chain of `Scope`'s.
|
|
#[inline]
|
|
pub fn unsafe_cast_var_name_to_lifetime<'s>(name: &str) -> &'s str {
|
|
// WARNING - force-cast the variable name into the scope's lifetime to avoid cloning it
|
|
// this is safe because all local variables are cleared at the end of the block
|
|
unsafe { mem::transmute(name) }
|
|
}
|