[pizza234]

If one sets the requirement of having manual memory management in a mixed language, then:

1. either they don't use any library, including the standard one,

2. or the (standard) libraries must be written in both manual and managed memory management versions.

Additionally, the language must include extra syntax for memory allocation and access. This doesn't event include safety-related semantics, like Rust, which would be very hard to bolt-in (language-wise).

I hardly see any advantage in Java/C# having this functionality; Oracle is actually putting lots of effort into improving their garbage collectors. Java does actually have manual memory management (through Unsafe), although it's rudimentary; for the reason mentioned, I doubt it will ever be improved/expanded.