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0 pointsthradams2y ago0 comments

In cake object and memory are two resources. We can for instance, delete the object and reuse the same memory.

For instance, this code is correct.

    #include <ownership.h> 
    #include <stdlib.h>

    struct X {
       char * owner text;
    };

    void x_delete(struct X * owner p)
    {
        if (p)
        {
           free(p->text);
           free(p);    
        }
    }

    int main() {   
       struct X * owner p = malloc(sizeof(struct X));
        
       p->text = malloc(10);

       free(p->text); //object text destroyed

       struct X x2 = {0};

       *p = x2; //x2 MOVED TO *p

       x_delete(p);   

       //no need to destroy x2
    }

#include <ownership.h> #include <stdlib.h> struct X { char * owner text; }; void x_delete(struct X * owner p) { if (p) { free(p->text); free(p); } } int main() { struct X * owner p = malloc(sizeof(struct X)); p->text = malloc(10); free(p->text); //object text destroyed struct X x2 = {0}; *p = x2; //x2 MOVED TO *p x_delete(p); //no need to destroy x2 }

0 comments

4 comments · 1 top-level

Arnavion2y ago· 3 in thread

    let p: Box<X> = Box::new(X { ... });

    let x2 = X { ... };

    // Moves x2 into the same memory as the first X.
    // The first X is automatically dropped as part of this assignment.
    // Also consumes x2 so x2 is not available any more.
    *p = x2;

    // Drops the X that was originally assigned to x2 and then moved into p.
    drop(p);

    // No need, nor is it possible, to destroy x2.

thradamsOP2y ago

Thanks for the rust sample. It looks very similar. Can the allocator be customized?

As I said I am not Rust specialist.

Also, in my understanding is that in Rust, sometimes a dynamic state is created when the object may or may not be moved.

In cake ownership this needs to me explicit ( and the destructor is not generated)

I also had a look at Rust in lifetime annotations. This concept may be necessary but I am avoiding it.

Consider this sample.

   struct X {  
     struct Y * pY;  
   };  
   struct Y {  
     char * owner name;  
   };

An object Y pointed by pY must live longer than object X. (Cake is not checking this scenario yet)

Also (classic Rust sample)

    int * max(int * p1, int * p2) {  
      return *p1 > *p2 ? p1 : p2;
    }

    int main(){  
       int * p = NULL;
       int a  = 1;
      {
         int b = 2;
         p = max(&a,  &b);
      }
      printf("%d", *p);
    }

This is not implemented yet but I want to make the lifetime of p be the smallest scope. (this is to avoid lifetime annotations)

   int * p = NULL;
   int a  = 1;
   {
      int b = 2;
      p = max(&a,  &b);
   } //p cannot be used beyond this point*

2 more replies

masklinn2y ago

And as bonus there is no temporal hole where you could access a null or dangling text.

Here it is as a runnable snippet: https://godbolt.org/z/fc4Gfxrfd

thradamsOP2y ago

In cake there is no temporal hole, we cannot reuse the deleted object. This prevents double free and use after free.

    int main() {   
       struct X * owner p = malloc(sizeof(struct X));
        
       p->text = malloc(10);

       free(p->text); //object text destroyed

       //p->text is on uninitialized state. 
       //cannot be used (except assignment)

       struct X x2 = {0};

       *p = x2; //x2 MOVED TO *p

       x_delete(p);

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0 comments

4 comments · 1 top-level

Arnavion2y ago· 3 in thread

    let p: Box<X> = Box::new(X { ... });

    let x2 = X { ... };

    // Moves x2 into the same memory as the first X.
    // The first X is automatically dropped as part of this assignment.
    // Also consumes x2 so x2 is not available any more.
    *p = x2;

    // Drops the X that was originally assigned to x2 and then moved into p.
    drop(p);

    // No need, nor is it possible, to destroy x2.

thradamsOP2y ago

Thanks for the rust sample. It looks very similar. Can the allocator be customized?

As I said I am not Rust specialist.

Also, in my understanding is that in Rust, sometimes a dynamic state is created when the object may or may not be moved.

In cake ownership this needs to me explicit ( and the destructor is not generated)

I also had a look at Rust in lifetime annotations. This concept may be necessary but I am avoiding it.

Consider this sample.

   struct X {  
     struct Y * pY;  
   };  
   struct Y {  
     char * owner name;  
   };

An object Y pointed by pY must live longer than object X. (Cake is not checking this scenario yet)

Also (classic Rust sample)

    int * max(int * p1, int * p2) {  
      return *p1 > *p2 ? p1 : p2;
    }

    int main(){  
       int * p = NULL;
       int a  = 1;
      {
         int b = 2;
         p = max(&a,  &b);
      }
      printf("%d", *p);
    }

This is not implemented yet but I want to make the lifetime of p be the smallest scope. (this is to avoid lifetime annotations)

   int * p = NULL;
   int a  = 1;
   {
      int b = 2;
      p = max(&a,  &b);
   } //p cannot be used beyond this point*

2 more replies

masklinn2y ago

And as bonus there is no temporal hole where you could access a null or dangling text.

Here it is as a runnable snippet: https://godbolt.org/z/fc4Gfxrfd

thradamsOP2y ago

In cake there is no temporal hole, we cannot reuse the deleted object. This prevents double free and use after free.

    int main() {   
       struct X * owner p = malloc(sizeof(struct X));
        
       p->text = malloc(10);

       free(p->text); //object text destroyed

       //p->text is on uninitialized state. 
       //cannot be used (except assignment)

       struct X x2 = {0};

       *p = x2; //x2 MOVED TO *p

       x_delete(p);

j / k navigate · click thread line to collapse