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Comment by throwawayk7h | Hacker News Reader

> Interface informality is the root cause of unsafety

I feel this frequently with C. I would love to formalize pointer use in interfaces. But Xr0's proposed syntax is clunky and not backward-compatible.

  void foo(int* x) ~ [ free(x); ];

Yikes... Why not

  // <xr0.h>
  #ifndef __XR0__
    #define freed
  #endif
  
  // my code:
  void foo(int* freed x);

Boom. Looks clean, easily readable, backward compatible with standard compilers.

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The reason for the new annotation syntax is the annotations are much richer in their details than merely stating when an object is freed by a function. They can express subtle preconditions, such as the expectation that a pointer refer to a region that is heap-allocated, or be a valid lvalue or rvalue, and so on, and also capture more general side effects.

As per the issue of backward-compatibility, Xr0 strips the annotations with a simple command: `0v -s`, producing C source that works with C compilers.

It would be nice to be able to compile all Xr0 code directly with a regular C compiler though. It's more convenient than running it through a program, which is a bit of a headache sometimes.

For complicated annotations, instead of

  void foo(int* x) ~ [ free(x); ];

They could do:

   #include <xr0.h>
   void foo(int* x) XR0( free(x); );

Then this will compile in a standard C compiler (assuming the XR0 macro is defined properly in xr0.h)

It's one more step in the build process. Maybe one day we'll imitate Zig and let C compilers be called via Xr0 though.

It also buys as the possibility of beauty. Shoehorning the annotations we're introducing into the preprocessor leads to constructions that aren't nice.

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