[Issue 481] New: Letting compiler determine length for fixed-length arrays

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=481

           Summary: Letting compiler determine length for fixed-length
                    arrays
           Product: D
           Version: 0.172
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla at digitalmars.com
        ReportedBy: wbaxter at gmail.com


There needs to be a way to tell the compiler to count up how many elements
there are in a fixed length array.  In C++ you use empty brackets, [], but in D
this means "create a dynamic array".  Sometimes you want a fixed-length array
but it's a pain to count up the elements by hand.  The main example is
embedding binary data, like images, into the program as code.

A possible syntax would be to use the pre-existing '$' or 'length' indicators
to specify that the length of the array should be the length of the
initializer:

   int arr[$] = [1,2,3,4];  // makes an int[4]
   int arr[length] = [1,2,3,4];  // ditto
   int[$] arr = [1,2,3,4];  //  ditto
   int[length] arr = [1,2,3,4];  // ditto

Another option would be to re-use the keyword auto.
   int arr[auto] = [1,2,3,4];  // makes an int[4]
   int[auto] arr = [1,2,3,4];  //  ditto

Using 'auto' makes sense in that the length really is part of the type of a
fixed-length array, so really what you're saying is "automatically deduce just
this part of the type for me".

Using 'auto' would also be extend naturally to associative arrays when/if there
are initializers for those.  For example:

   int[auto] str_to_num = [ "one":1, "two":2, "three":3 ];

This would specify that value type is int, but let the key type be
automatically deduced from the initializer.


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