[Issue 5204] New: Inherited out contract requires lvalue result?

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=5204

           Summary: Inherited out contract requires lvalue result?
           Product: D
           Version: D2
          Platform: x86
        OS/Version: Windows
            Status: NEW
          Severity: major
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: ah08010-d at yahoo.com


--- Comment #0 from Austin Hastings <ah08010-d at yahoo.com> 2010-11-11 16:04:09 PST ---
Using 2049, this code:
==========
module scratch;

interface collection( ValueT ) {
        alias collection!( ValueT ) collection_t;
        collection_t clear()
                out( result ) { assert( result.length == 0 ); }
        @property size_t length();
}

interface mapping( KeyT, ValueT ) : collection!( ValueT ) { /* ... */ }

class aamap( KeyT, ValueT ) : mapping!( KeyT, ValueT ) {
        alias aamap!( KeyT, ValueT ) aamap_t;

        aamap_t clear( ) { return this; }
}

void main() {
        alias aamap!( string, int ) aa_str2int;
}
==========
produces these diagnostics:
==========
$ dmd -run scratch.d
scratch.d(15): Error: cast(collection)__result is not an lvalue
scratch.d(19): Error: template instance scratch.aamap!(string,int) error
instantiating
==========
As I understand it, I should be able to code a function like int foo() { return
1+1;} and have an out contract attached. So I don't understand why there is any
consideration of the result ever being an lvalue.

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