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Is there a way to fetch objects w/o default constructor? [message #18052]

Mon, 08 September 2008 11:25

Mindtraveller
Messages: 917
Registered: August 2007
Location: Russia, Moscow rgn.

Experienced Contributor

Simplified code as a description of problem:

class Project
{
    Project(TabCtrl &tabs) {/*add new tab with Project controls*/}
};

class App
{
    void Serialize (Stream &stream) {stream % projects;} //ERROR: no default constructor available
    Array<Project> projects;
    TabCtrl        mainTabs;
};

Is there a way I can fetch my Project objects with auto-adding to the tabs?

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Re: Is there a way to fetch objects w/o default constructor? [message #18054 is a reply to message #18052]

Mon, 08 September 2008 19:23

mirek
Messages: 14291
Registered: November 2005

Ultimate Member

Mindtraveller wrote on Mon, 08 September 2008 05:25

Simplified code as a description of problem:

class Project
{
    Project(TabCtrl &tabs) {/*add new tab with Project controls*/}
};

class App
{
    void Serialize (Stream &stream) {stream % projects;} //ERROR: no default constructor available
    Array<Project> projects;
    TabCtrl        mainTabs;
};

Is there a way I can fetch my Project objects with auto-adding to the tabs?

Yes, but not really recomended Smile

The trick would be to implement your own Array serialization, using "new" variant of Add.

Something like:

if(s.IsLoading())
    projects.Clear();
int count = projects.GetCount();
s % count;
for(int i = 0; i < count; i++)
    if(s.IsStoring())
        s % projects[i];
    else
        s % projects.Add(new Project(tabs));

(I would rather find some other solution. IMO, except special cases, classes should have default constructors).

Mirek

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Re: Is there a way to fetch objects w/o default constructor? [message #18059 is a reply to message #18054]

Tue, 09 September 2008 08:47

Mindtraveller
Messages: 917
Registered: August 2007
Location: Russia, Moscow rgn.

Experienced Contributor

So what "right", or "typical" solution of such a common problem is recommended? Just to make default constructor along with something like void Setup(.....) ?

stream % projects;

if(stream.IsLoading())
{
    for (int i=0; i<projects.GetCount(); ++i)
        projects.Setup(......);
}

This method has one big drawback: I can`t hold any references inside Project class because I can`t initialize them in constructor. In my previous example this means i.e. I can`t hold tabs reference inside Project which is very uncomfortable. Using simple pointer and setting it inside Setup() is no good too.

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Re: Is there a way to fetch objects w/o default constructor? [message #18062 is a reply to message #18059]

Tue, 09 September 2008 08:57

mirek
Messages: 14291
Registered: November 2005

Ultimate Member

Mindtraveller wrote on Tue, 09 September 2008 02:47

So what "right", or "typical" solution of such a common problem is recommended? Just to make default constructor along with something like void Setup(.....) ?

Well, that is what I would use.

Quote:

stream % projects;

if(stream.IsLoading())
{
    for (int i=0; i<projects.GetCount(); ++i)
        projects.Setup(......);
}

Well, I actually do not really know what degree of flexibility is needed... Is the number of projects fixed and only the content is changing? Too little info to discuss the solution.

Quote:

That is correct. Personally I would do this sacrifice in order to avoid "Add(new)" variant. (Well, as you might have noticed, I tend to judge the quality of code by number of new/delete statements Smile

Mirek

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