generic setVariable

[Kamran]

Hi,

I have hundreds of variables inside a class (integer, float) and a long
range of set/get functions to manipulate their values.
What I am wondering about is whether there is a way in C++ to have
generic setVariable function which take a text string as a variable and
find the appropriate variable and either set or get its value.
I know that dynamic name resolution is not possible in C++ but is
there any other way to do this ? There are far too many variables
to do it individually one by one.

Thanks in advance

Kamran

[mlimber]

Kamran wrote:

I have hundreds of variables inside a class (integer, float) and a long
range of set/get functions to manipulate their values.

Sounds like it might be a design problem.

What I am wondering about is whether there is a way in C++ to have
generic setVariable function which take a text string as a variable and
find the appropriate variable and either set or get its value.
I know that dynamic name resolution is not possible in C++ but is
there any other way to do this ? There are far too many variables
to do it individually one by one.

You could use a std::map of boost::any's (or boost::variant; cf.
http://boost.org):

class A
{
std::map<std::string, boost::anyprop_;
public:
template<typename T>
void SetVar( const std::string& s, const T& t )
{
prop_[ s ] = t;
}

// ...
};

Cheers! --M

[Rolf Magnus]

Kamran wrote:

>
Hi,

I have hundreds of variables inside a class (integer, float) and a long
range of set/get functions to manipulate their values.
What I am wondering about is whether there is a way in C++ to have
generic setVariable function which take a text string as a variable and
find the appropriate variable and either set or get its value.
I know that dynamic name resolution is not possible in C++ but is
there any other way to do this ? There are far too many variables
to do it individually one by one.

The point of making member variables privat is to encapsulate them, i.e.
separate the interface from the impementation. If you want set/get
functions for every member variable, you can just as well make them public,
because you're exposing them anyway.

[Howard]

"Rolf Magnus" <ra******@t-online.dewrote in message
news:ea*************@news.t-online.com...

Kamran wrote:

>>
Hi,

I have hundreds of variables inside a class (integer, float) and a long
range of set/get functions to manipulate their values.
What I am wondering about is whether there is a way in C++ to have
generic setVariable function which take a text string as a variable and
find the appropriate variable and either set or get its value.
I know that dynamic name resolution is not possible in C++ but is
there any other way to do this ? There are far too many variables
to do it individually one by one.

The point of making member variables privat is to encapsulate them, i.e.
separate the interface from the impementation. If you want set/get
functions for every member variable, you can just as well make them
public,
because you're exposing them anyway.

Not always. It sounds like that's the case here, but I've had similar code
where there were side effects to setting the members, so I had to use setter
functions to change them. (Also, there are cases where the "variables" are
actually fields in a database hidden behind the class, but again, this case
doesn't sound like one of those cases.)

(As an aside, I really liked Delphi's feature of having "properties", which
looked to the calling code as if they were just members, but which could be
implemented via functions if desired. They also allowed for disabling
reading and/or writing the members. Very convenient, IMO.)

-Howard

[Kamran]

mlimber wrote:

Kamran wrote:

>>I have hundreds of variables inside a class (integer, float) and a long
range of set/get functions to manipulate their values.

Sounds like it might be a design problem.

Well, it is geophisical data and the number of parameters that can
change is huge. There is really not much I can do about that.

>

>>What I am wondering about is whether there is a way in C++ to have
generic setVariable function which take a text string as a variable and
find the appropriate variable and either set or get its value.
I know that dynamic name resolution is not possible in C++ but is
there any other way to do this ? There are far too many variables
to do it individually one by one.

You could use a std::map of boost::any's (or boost::variant; cf.
http://boost.org):

class A
{
std::map<std::string, boost::anyprop_;
public:
template<typename T>
void SetVar( const std::string& s, const T& t )
{
prop_[ s ] = t;
}

// ...
};

Cheers! --M

Thanks for the tip. I'll have a look at that.

Kamran

[Kamran]

Rolf Magnus wrote:

Kamran wrote:

>>Hi,

I have hundreds of variables inside a class (integer, float) and a long
range of set/get functions to manipulate their values.
What I am wondering about is whether there is a way in C++ to have
generic setVariable function which take a text string as a variable and
find the appropriate variable and either set or get its value.
I know that dynamic name resolution is not possible in C++ but is
there any other way to do this ? There are far too many variables
to do it individually one by one.

The point of making member variables privat is to encapsulate them, i.e.
separate the interface from the impementation. If you want set/get
functions for every member variable, you can just as well make them public,
because you're exposing them anyway.

These are not member variables that are part of internal class operation
but variables that a user should and could manipulate. Whether I define
them public or private and let a set of functions do the value
manipulation the amount of work is the same. I have to have a mechanism
to set their values to new ones. This is what I want to reduce (coding)
to have a more managable code. Lets say I have a class:

class A {
..
..
..
int var1;
float var2;
double var3;

[Julián Albo]

Kamran wrote:

to set their values to new ones. This is what I want to reduce (coding)
to have a more managable code. Lets say I have a class:

class A {
.
.
.
int var1;
float var2;
double var3;
.
.
.
short var100;
.
.
.
};

How does one go changing those variable values, public or private
without doing that explicitally (if public) or through an interface ?

You can put only a set and a get function for each variable type, put any
type in an array, define an enumeration and use it to select the variable.
Something like:

enum IntVars { Var1 ... };
enum FloatVars { Var2 ... };
emum DoubleVars { Var3 .. };

int intvars [whatever];
int getVar (IntVars v);
{
return intvars [v];
}
void setVar (IntVars v, int value)
{
intvars [v]= value;
}

a.setVar (Var1, 1);

If the variables have meaningful names the code will be more legible than
this sample.

--
Salu2

[Florian Keßeler]

Kamran schrieb:

>
Hi,

I have hundreds of variables inside a class (integer, float) and a long
range of set/get functions to manipulate their values.
What I am wondering about is whether there is a way in C++ to have
generic setVariable function which take a text string as a variable and
find the appropriate variable and either set or get its value.
I know that dynamic name resolution is not possible in C++ but is
there any other way to do this ? There are far too many variables
to do it individually one by one.

Thanks in advance

Kamran

You may put your attributes into a map and use the map to get the
references to your variables.

But this will
- break encapsulation, since the map doesn't know anything about private
oder protected members
- slow down your program, because lookup in the map will take
logarithmic time to access, where "real" member-access takes constant time.

If you really have hundreds of variables, which are also directly
accessibly via setters/getters, you might as well have a major design
problem. Look at your code and check if you really need all these
variables or if you can combine them into other classes.

Usually you don't need public access to all your attributes, if you do
need it, you may want to check whether you understood object-orientation....

Florian