[Issue 9251] New: An immutable arrays concatenation to produce an immutable implicitly castable to mutable?

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=9251

           Summary: An immutable arrays concatenation to produce an
                    immutable implicitly castable to mutable?
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: rejects-valid
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2013-01-01 08:47:30 PST ---
void main() {
    string s1 = "abc";
    char[] s2 = s1 ~ s1;
}



DMD 2.061alpha gives:

test.d(3): Error: cannot implicitly convert expression (s1 ~ s1) of type string
to char[]


A concatenation allocates a new array, so I think it should be a strongly pure
operation. So maybe a string concatenation should return a string that's
implicitly castable to char[]. (While usually in D with purity you have mutable
things that are implicitly castable to immutable). Is this possible and safe?

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