[Issue 3474] New: PATCH: Implement opDollar for struct and class indexing operations

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=3474

           Summary: PATCH: Implement opDollar for struct and class
                    indexing operations
           Product: D
           Version: 2.036
          Platform: Other
        OS/Version: All
            Status: NEW
          Keywords: patch
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: clugdbug at yahoo.com.au


--- Comment #0 from Don <clugdbug at yahoo.com.au> 2009-11-05 07:33:37 PST ---
Created an attachment (id=491)
Patch against DMD2 svn 240.

The attached patch allows usage of $ inside opIndex and opIndexAssign in
structs and classes.
Any usage of $ becomes a call to an opDollar function.
If multi-dimensional indexing is possible, the $ symbol instantiates a template
called opDollar(int dim)().

x[ $-3, $-5, $-6] becomes  x.opIndex(x.opDollar!(0)() - 3, x.opDollar!(1)() -
5, x.opDollar!(2)() -6);

Note that since opDollar is a template, it may return different types for
different indices...

As a convenience, if a class or struct ONLY supports single-dimension indexing,
a non-templated opDollar() can be used instead.

x[ $-5 ]  can become   x.opIndex( x.opDollar() - 5 );

(If a opDollar!(int n)() is available, it will be used instead. There's no
ambiguity: the compiler won't let you define both template and function
opDollar, since they both have no arguments).

Some implementation notes:
(1) $ is evaluated lazily for each dimension.  x[4,  $+3*$ - foo($), 6] will
only make one call to opDollar.
(2) BUG 3326: "$ in delegate literal causes Access Violation" does NOT apply to
this code. You can do all kinds of nasty stuff with $ and it seems to work.
(3) It is possible to nest multi-dimensional indexing. x[$-2, y[$-6, $-9], $-2]
works.
(4) I have NOT implemented $ inside opSlice(), opSliceAssign().
It could be done, but I believe those language features need work. They don't
permit multi-dimensional slicing. I think they should be removed, and the
functionality folded into opIndex.
(5) How it works:
x[ $-3, 5, $-6]= "abc" actually becomes:
x.opIndexAssign("abc", (auto __dollar = x.opDollar!(0)();, __dollar - 3), 5,
(auto __dollar = x.opDollar!(2)(); _dollar - 6)).

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