Summary: std.range.chain shouldn't have opIndexAssign if
                    arguments aren't mutable.
           Product: D
           Version: 2.032
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Keywords: patch
          Severity: normal
          Priority: P2
         Component: Phobos

--- Comment #0 from David Simcha <> 2009-09-11 07:50:39 PDT ---
import std.range;

void main() {
    immutable(uint)[] foo = [1,2,3,4,5];
    immutable(uint)[] bar = [6,7,8,9,10];
    auto baz = chain(foo, bar);

C:\dmd2\windows\bin\..\..\src\phobos\std\range.d(930): Error:
this._input._field_field_0[index] isn't mutable
C:\dmd2\windows\bin\..\..\src\phobos\std\range.d(930): Error:
this._input._field_field_1[index] isn't mutable

This is too simple to fix to do a formal patch, but here's an "inline patch":

/**Tests whether a type is mutable, i.e. not const or immutable.  This is only
 * tested at the shallowest level, not transitively.  For example, an
 * immutable(uint)[] would be considered mutable.*/
template isMutable(T) {
    enum isMutable = !is(T == const(T));

unittest {
    static assert(isMutable!(ElementType!(uint[])));
    static assert(isMutable!(ElementType!(float[])));
    static assert(!isMutable!(ElementType!(string)));
    static assert(isMutable!(ElementType!(string[])));
    static assert(!isMutable!(ElementType!(const(char)[])));
    static assert(isMutable!string);

And in std.range.chainImpl:

static if (allSameType) void opIndexAssign(ElementType v, uint index)

should be changed to

static if (allSameType && isMutable!(ElementType))
void opIndexAssign(ElementType v, uint index)

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