• d-bugmail puremagic.com (44/44) Nov 27 2013 https://d.puremagic.com/issues/show_bug.cgi?id=11615

d-bugmail puremagic.com writes:

https://d.puremagic.com/issues/show_bug.cgi?id=11615

           Summary: Syntax to indicate auto return type is const
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody puremagic.com
        ReportedBy: joseph.wakeling webdrake.net



2013-11-27 01:28:42 PST ---
This enhancement request is a result of the following discussion on D.learn:
http://forum.dlang.org/thread/mailman.34.1385370339.3242.digitalmars-d-learn puremagic.com

Consider a struct or class which contains a method that allows one to access
internal data, e.g.:

    struct Foo
    {
        int[] _arr = [0, 1, 2, 3, 4];

        auto arr()  property
        {
            return _arr;
        }
    }

The problem with this is that what is returned by the .arr property allows
write access to the internal array _arr.  This can be solved by making the
return type declaration more explicit:

    const(int)[] arr()  property
    {
        return _arr;
    }

However, it would be nice to be able to indicate and obtain such non-writeable
return types with the use of auto.  The syntax const(auto) seems nice here. 
The fundamental goal would be simply: "You can't write to this data via this
handle."  The aim is to simplify generic programming situations by allowing the
programmer to specifically protect against any accidental opening up of private
data to external write access.

Note that applying the regular const keyword won't work here, because this
implies a const _method_ (which is a stricter requirement than just a const
return type).

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