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What are the feature of C Programming language that break the type-safety and prohibits practical garbage collection from being added to the language? Explain.
Firstly, I don’t understand the relationship between type-safety and garbage collection. I’d appreciate if someone can help me with that.
You can do garbage collection in C. It is called conservative garbage collection. The trick is to treat any data that looks like a pointer as if it were in fact a pointer, and not reclaim any memory that is reachable through it. There are two problems: first, you cannot move data around (i.e., compaction), because of the uncertainty of whether something that looks like a pointer is in fact a pointer (so updating it to point to a new location could result in data corruption).
The type-safety problem is that it is possible for a C programmer to store a pointer to an int, perform math on it, and then restore the pointer (as in:
ptrdiff_t d = (ptrdiff_t) ptr; ptr = NULL; d += 42; /* GC here would be bad */ d -= 42;) This pointer hiding could lead a conservative garbage collector to prematurely reclaim memory that was only reachable through that pointer.