how do I tell if something is lvalue?

[Steven Schveighoffer via Digitalmars-d-learn]

On 2/1/16 5:20 PM, tsbockman wrote:
> On Sunday, 31 January 2016 at 22:11:45 UTC, Steven Schveighoffer wrote:
>> Thanks! I was surprised this is not straightforward.
>>
>> -Steve
>
> For function return values, at least, you can do this:
>
> import std.traits, std.stdio;
>
> int foo()
> {
>      return 0;
> }
>
> ref int bar()
> {
>      static int x = 0;
>      return x;
> }
>
> enum isRetByRef(alias func) = (functionAttributes!func &
> FunctionAttribute.ref_) != 0;
>
> void main()
> {
>      writeln("foo: ", isRetByRef!foo);
>      writeln("bar: ", isRetByRef!bar);
> }
>
> (DPaste: http://dpaste.dzfl.pl/2aa8d3553a12)

Thanks. In my case, I need to treat fields and properties that return by 
ref the same way.

What I wanted essentially was a template constraint that says "this type 
has a member named foo, and t.foo is an lvalue"

-Steve