import std.conv;

void main()
{
    assert( to!string( cast(const int)1) == "1" );
}

errors:
src/phobos/std/conv.d(2580): Error: variable std.conv.to!(immutable(char)[],const(int)).to.u cannot modify const
src/phobos/std/conv.d(5): Error: template instance std.conv.to!(immutable(char) [],const(int)) error instantiating


Possible fix:

@@ -2570,11 +2570,11 @@
         return to!T(cast(Unsigned!(S)) value);

     alias Unqual!(ElementType!T) Char;
     Char[1 + S.sizeof * 3] buffer;

-    auto u = -cast(Unsigned!S) value;
+    Unqual!S u = -cast(Unsigned!S) value;
     uint ndigits = 1;
     while (u)
     {
         immutable c = cast(char)((u % 10) + '0');
         u /= 10;