On Wednesday, 31 October 2012 at 07:19:19 UTC, Jacob Carlborg
wrote:
On 2012-10-31 02:53, Peter Summerland wrote:
The order of the fields is rearranged for packing. Does that
affect the
tupleof property? The example in http://dlang.org/class.html
for Class
properties tulpleof seems to implie that the the fields the
returned
Expression Tuple are arranged in lexical order (i.e., as
defined by the
programmer in the class definition). Is this always true for
classes?
What about structs?
I don't know. But I would not count on the order of tupleof. I
would consider that implementation defined.
Thanks for the help.
Should the the following example, taken from the D Language
Reference, be considered incorrect or at least misleading? It
clearly depends on lexical ordering of the returned fields:
Class Properties
The .tupleof property returns an ExpressionTuple of all the
fields in the class, excluding the hidden fields and the fields
in the base class.
class Foo { int x; long y; }
void test(Foo foo) {
foo.tupleof[0] = 1; // set foo.x to 1
foo.tupleof[1] = 2; // set foo.y to 2
foreach (x; foo.tupleof)
writef(x); // prints 12
}
It would be nice if the Language Reference was specific on this
point. I am aware that the order of the members returned by
__traits(allMembers, D) is not defined (per the LR). But that is
a larger, more complex list.
I am just beginning with D, but I think having the tupleof
property for classes and structs return their fields in lexical
order might be useful.
E.g., I have written a "scan" function to load up a struct or
class from a row returned by a database query. I have, say,
scan!"x,y,z"(obj) to load data into fields x,y,z of obj. Based on
the example above and by experimenting, it appears that at least
for dmd running on Linux, that the fields returned by tupleof are
indeed in lexical order. That allowed me to have a "" default
for the string of field names which indicates that all the fields
should be loaded. I.e., I have scan!""(obj), which can be written
scan(obj). Again, it seems to work for simple classes and structs
with Dmd on Ubuntu.
Don't get me wrong -- I'll be happy without the default version
if that is the answer. I'm not suggesting any changes.
