Bypassing the postblit?

[monarch_dodra]

On Sunday, 29 December 2013 at 18:40:07 UTC, Maxim Fomin wrote:
> On Sunday, 29 December 2013 at 16:22:04 UTC, Ritu wrote:
>> I have a struct that wraps a class object and lazily 
>> initializes it. Now in case the struct instance is passed as 
>> an argument to a function and it has not been initialized yet, 
>> the default copy constructor and the postblit do not offer a 
>> possibility to initialize the class object before copying.
>
> Why this is a problem? You can create function which return 
> class field from struct wrapper and make such function alias 
> this, in addition postblit should allocate new class. The fact 
> that original struct may have null value is irrelevant if 
> copying is made correctly.

It's a problem for "reference semantic structs" that need to be 
initialized. This is actually a "well know" and often encountered 
problem.

It strikes things like Appende, Array, and also built in AA's.

void foo(Appender!(int[]) app)
{
     app.put(1);
}

void main()
{
     Appender!(int[]) app1;
     Appender!(int[]) app2 = appender!(int[]);
     foo(app1);
     foo(app2);
     assert(app1.data == [1]); //Fails
     assert(app2.data == [1]); //Passes
}