#stack-overflow #box #heap #initialization #array #values #box-t

no-std boxify

Place your values directly on the heap without creating them on the stack first

1 unstable release

0.1.0 Feb 6, 2024

#353 in Memory management

MIT license

104 lines


This crate provides a macro to initialize your Box<T> on the heap without having to have it on the stack before. This allows easily putting big arrays or structs containing them into a Box without overflowing the stack:

// this would overflow the stack:
// let e = Box::new(Example {
//     huge_array: [42; 1024 * 1024 * 1024],
// });

// this does not:
let e = boxify::boxify!(Example {
    huge_array: [42; 1024 * 1024 * 1024],

Supported structures

Currently, this supports tuples, arrays and structs, even deeply nested ones. Take a look at the examples folder to see what's possible. All other types are constructed on the stack and put into the box later.

Known Limitations

  • Enums are not supported and can never be fully supported since their layout in memory is not fully specified.
  • Only calls of lowercase function names and uppercase tuple struct instantiations are fully supported.
    This limitation is necessary because there is no way to determine whether something is a function call or a tuple struct instantiation and both have to be handled differently, so this crate just uses the naming as a heuristic. The macro will cause a compiler error if it encounters a function where a struct was expected to prevent unsoundness. A lowercase tuple struct instantiation will quietly allocate on the stack and move it to the heap.
  • Struct update syntax, aka Test { ..test } is not allowed and causes a compiler error. This is because the macro needs to know all of the struct fields to fill them.


~22K SLoC