• Kevin Bealer <kevinbealer gmail.com> Mar 25 2008
• Walter Bright <newshound1 digitalmars.com> Mar 25 2008
• Kevin Bealer <kevinbealer gmail.com> Mar 25 2008

Kevin Bealer <kevinbealer gmail.com> writes:

Walter Bright Wrote:

 Clay Smith wrote:
 Is SafeD just a label for the programmer selectively using D features?


 Yes, but it would also be enforced by a compiler switch.


When a project gets to a certain size you will often want to add some unsafe
code, but a switch suggests that the whole file (or project) now has to be safe
or unsafe as a single block.  A version statement could be used to mark the
unsafe areas of an otherwise "safe" file:

version(unsafe) {
some code;
}

or 

version(unsafe):

This allows islands of unsafety.  A compiler switch could be defined as a way
of disabling
all unsafe code within a module, then an "unsafe" marker in a class could
indicate parts of the API that are hidden from "safe" code.

class MyVector {
    int foo();
    int bar();

unsafe:
    int baz();
};

MyVector v...;
v.baz(); // error

version(unsafe) {
   b.baz(); // okay
}

Is the "in" operator (for AAs) safe?

Kevin

Walter Bright <newshound1 digitalmars.com> writes:

Kevin Bealer wrote:
 Is the "in" operator (for AAs) safe?


Good question. Andrei thinks it needs to be redesigned.

Kevin Bealer <kevinbealer gmail.com> writes:

Walter Bright Wrote:

 Kevin Bealer wrote:
 Is the "in" operator (for AAs) safe?


 Good question. Andrei thinks it needs to be redesigned.


Hmmm.....

Pointers have several useful "APIs".

1. The communicate an address of an object of a particular type.
2. They can be null, which is a way to support an "optional" value.
3. They support conversion of class pointers (up and down inheritance trees).
4. They support casting to other pointer types (such as reading an int as a
char[4]).
5. They support pointer arithmetic (writing malloc() like code, array indexing).

It seems like 1 and 2 are available in Java, and 3 is available but the
compiler or run time code supervises the operation to make sure it looks
correct.  In Java, 4 and 5 are missing,
but arrays can still be indexed.

[  Off topic: A "safe" (from a memory management POV) language could allow a
subset of
   4 and even 5 -- you could convert an int to a char[4] or an int[10] to a
char[40], or vice 
   versa, for example.  This prevents "walking off" an array and secondary
(dangling ptr)
   corruption but still allows (some) clever things (like writing a limited
version of malloc())
   to be done.

   To be "safe", you would want to prevent internal pointers -- casting int[10]
to int*[10],
   or to something like int[][5] (assuming int[] is struct { int* x; int
length; }) should fail. ]

Getting back to the AA question, we'd like features 1 and 2 -- null or a real
value.  Maybe "in" should return a T[]?  The ptr field is the current "in"
return value, the length field is just 0 or 1.  The AA structure could even
contain a T[1] internally.  Since array indices are always checked in safe
mode, the user gets an index bounds error if they dereference it, which even
seems kind of correct for an associative array -- your key is "out of bounds"
by not being present...

T[] found = key in container;

: if (found) { // same as ptr syntax...
:     // swap in a new value
:     read_me = found[0];
:     found[0] = write_me;
: } else {
:     read_me = found[0];  // oops -- array bound error!
: }

(Of course, there's the backward compatibility question.)

Kevin