• d-bugmail puremagic.com (37/37) Dec 11 2010 http://d.puremagic.com/issues/show_bug.cgi?id=5342

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=5342

           Summary: std.array does not respect immutable/const string
                    qualifiers using front/back/etc
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Phobos
        AssignedTo: nobody puremagic.com
        ReportedBy: sandford jhu.edu



Essentially, the ElementType! of all strings is a mutable dchar, even if the
string itself is immutable. This means that generic code, like
isAssignable!(ElementType!string, ElementType!string) passes when it shouldn't. 

Here is a simple template make fixing this a whole lot less painful.

/// Apply the const-ness of Src to type Dst
template Requal(Src,Dst) {
    static if(is(             Unqual!Src  == Src)) alias              Dst 
Requal;
    static if(is(const        Unqual!Src  == Src)) alias const(       Dst)
Requal;
    static if(is(immutable    Unqual!Src  == Src)) alias immutable(   Dst)
Requal;
    static if(is(shared       Unqual!Src  == Src)) alias shared(      Dst)
Requal;
    static if(is(shared(const Unqual!Src) == Src)) alias shared(const Dst)
Requal;
}

// example
Requal!(typeof(A.init[0]), dchar) front(A)(A a) if (is(typeof(A[0])) &&
isNarrowString!A)

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