On Monday, 28 January 2013 at 20:21:19 UTC, Philippe Sigaud wrote:
Just testing whether t.M can be assigned to something (ie, is
it a value?)
I use '_' as a variable name to indicate I don't care for
it's precise
name/value. It's just a placeholder.
Ok, I must be missing something, why "t.D" or is this just a
typo?
Ark, typo, sorry about that.
And secondly wouldn't "x.M = y.M" take care of checking that
the member can be
read and written to ?
t.M = t.M? Yes, you're right.
Also, doesn't your solution require T to be default
constructible ?
Yes, but if a type is not default-constructible, I don't know
how to test it.
Maybe testing on typeof(T.M)?
My solution to that was to try and compile the definition of a
delegate :
__traits(
compiles,
"( ref T x ){ x." ~ M ~ " = x." ~ M ~ "; }"
);
I had originally provided two arguments to the delegate (using "(
ref T x, ref T y){ x.M = y.M; }") to avoid self assignment but
It's not necessary. This seems to work as it returns the right
result and does not require T to be default constructible.
Just thought of the fact that I didn't try this with a class (I
don't know if you're allowed to write "ref T x" if T == class),
but you can always specialize hasDataMember with constraints or
use static if.
Using 2.061 here.
Well that was the problem! I was still using 2.060 which seems
to have the
bug. Now that I've moved to 2.061 everything works as expected
(your
implementation and mine).
Great!
Many thanks for your help on this again.
