How to copy object of class A to another object of class B?

[aldanor via Digitalmars-d-learn]

On Wednesday, 28 January 2015 at 11:30:13 UTC, Marc Schütz wrote:
> On Wednesday, 28 January 2015 at 09:44:29 UTC, zhmt wrote:
>> It is boring coding, I want a solution to copy them 
>> automatically:
>> void copyObj(SRC,DEST)(SRC src,DEST dest)
>> {
>> 	foreach (i, type; typeof(SRC.tupleof)) {
>> 		auto name = SRC.tupleof[i].stringof;
>> 		__traits(getMember, dest, name) =  __traits(getMember, src, 
>> name);
>> 		writeln(name);
>> 	}
>> }
>>
>> Unfortunitely, it doesnt work,  how to improve it?
>
> Haven't tested it, but the `auto name = ...` part is likely to 
> be the problem. By using `auto`, your declaring a runtime 
> variable, which you then later try to use with 
> `__traits(getMember, ...)`, which expects a value known at 
> compile time. Try using `alias name = ...`, or if that fails, 
> just repeat the expression `SRC.tupleof[i].stringof` wherever 
> `name` occurs (though I'm sure there is a nicer way).

And if the alias doesn't work directly, you can always use a 
well-known hack:

     alias Alias(T) = T;
     alias Alias(alias T) = T;

so then this works:

     alias member = Alias!(__traits(getMember, Parent, "child"));

Idk if it's a feature or a bug of how getMember works but I had 
to use this numerous times.