[nickez]

Yes, don't use the std lib (or more specifically the alloc crate) and don't use types like floats and u128.

[bonzini]

Is it possible to use Box (which is special cased in many places in the language and thus cannot be replaced, unlike for example Arc) without the alloc crate?

[myrrlyn]

a replacement to `alloc` would define a `Box` structure and tag it as `#[lang = "box"]` but not define any crashy APIs. this would accomplish the goal, but is an annoying patch that `alloc` should work to obviate upstream