Hecs World currently allows for "unsafe" component access via immutable references

[cart]

This isn't actually a memory safety problem because hecs also has runtime safety checks, but in some contexts it is useful to provide "immutable only" world references. For example, render graph nodes currently receive an &World reference, which was intended to be an immutable-only reference. Graph nodes are scheduled to run in parallel based on graph dependencies, so mutable access to components could cause undefined behavior. With legion &World was truly immutable. Which hecs, &World is "mutable with runtime safety checks".

To fix this i think we have two choices:

• modify World to label unsafe access as literally "unsafe"
• add an ImmutableWorld wrapper that only allows read actions

[Ratysz]

For what it's worth, I opted for a wrapper to solve a similar problem in yaks (I wanted to disallow doing anything that would break invariants the executor assumes within a system).

[DJMcNab]

I think this is fixed now (in #504?). We ended up taking approach 1.

[cart]

Yeah now that we rely on lifetimes in "safe" code to protect storage access, we can close this. Thanks for the follow up!