Slices and arrays problems?

[Ali Çehreli]

On 07/01/2013 10:34 AM, Damian wrote:

 > void testref(ref int[] arr)
 > {
 >      arr[0] = 1;
 > }
 >
 > void test(int[] arr)
 > {
 >      arr[0] = 1;
 > }
 >
 > void main()
 > {
 >      //int[] buffer1 = new int[4]; // This works
 >      int[4] buffer1; // This doesn't
 >      int[4] buffer2;
 >
 >      testref(buffer1);

When that call is made, a slice would have to be created to represent 
all of the elements of the fixed-length array buffer1. A slice would be 
needed because buffer1 is not a slice but testref() takes a slice.

By the simplest definition, that slice is an rvalue because it is not 
defined as a variable in the program.

And rvalues cannot be bound to non-const references. (If I am not 
mistaken not even to const references yet, if ever.)

 >      test(buffer2);

Similarly, when that call is made, a slice is created. The difference 
is, because the parameter is by-value, the slice gets copied to test(). 
Now there is no problem because 'arr' is just a local variable of test().

(Note that when I say a slice is created or a slice is copied, they are 
very cheap operations. A slice is nothing but the number of elements and 
a pointer to the first one of those elements. Just a size_t and a pointer.)

 >
 >      assert(buffer1[0] == 1);
 >      assert(buffer2[0] == 1);
 > }
 >
 > I'm not sure why my code doesn't work?? Isn't the buffer just an array
 > with a fixed length? DMD is telling me 'buffer1 is not an lvalue'. The
 > non ref version works fine?!

Ali