search of a workaround

[Namespace]

This works so far:

auto funcAttr = functionAttributes!(fun);
if (FunctionAttribute.pure_ & funcAttr) s ~= " pure";
if (FunctionAttribute.nothrow_ & funcAttr) s ~= " nothrow";
if (FunctionAttribute.ref_ & funcAttr) s ~= " ref";
if (!isMutable!(typeof(fun))) s ~= " const";

But it's curious that FunctionAttributes has no const, immutable, 
inout or shared...