gecko-dev/third_party/rust/inplace_it

Inplace it!

Place small arrays on the stack with a low cost!

The only price you should pay for this is the price of choosing a type based on the size of the requested array! This is just one match and call!

What?

This crate is created for one purpose: allocating small arrays on the stack. The simplest way to use it is:

use inplace_it::{inplace_or_alloc_array, UninitializedSliceMemoryGuard};

inplace_or_alloc_array(
    150, // size of needed array to allocate
    |mut uninit_guard: UninitializedSliceMemoryGuard<u16>| { // and this is consumer of uninitialized memory
        assert_eq!(160, uninit_guard.len());
        
        {
         // You can borrow guard to reuse memory
         let borrowed_uninit_guard = uninit_guard.borrow();
         // Let's initialize memory
         // Note that borrowed_uninit_guard will be consumed (destroyed to produce initialized memory guard)
         let init_guard = borrowed_uninit_guard.init(|index| index as u16 + 1);
         // Memory not contains elements [1, 2, ..., 160]
         // Lets check it. Sum of [1, 2, ..., 160] = 12880
         let sum: u16 = init_guard.iter().sum();
         assert_eq!(sum, 12880);
        }
        
        {
         // If you don't want to reuse memory, you can init new guard directly
         let init_guard = uninit_guard.init(|index| index as u16 * 2);
         // Memory not contains elements [0, 2, 4, ..., 318]
         // Lets check it. Sum of [0, 2, 4, ..., 318] = 25440
         let sum: u16 = init_guard.iter().sum();
         assert_eq!(sum, 25440);
        }
    }
)

Why?

Because allocation on the stack (i.e. placing variables) is MUCH FASTER then usual allocating in the heap.

Moar!

You can read the API reference for more details or create an new issue to submit a bug, feature request or just ask a question.

Release notes

0.3.2

• Placing of uninit memory moved out from try_inplace_array to disallow compiler to optimize it.

0.3.1

• Initialize with an exact-size iterator.

0.3.0

• API safety. No more unsafe external functions.
• Drop correctness. No more dropping of uninitialized memory.

0.2.2

• Fixed drop-correctness for safe functions. Now unsafe function do not drop your data but safe function do it correctly.