Pulling the type declaration out of a variable?

[Steven T. Hatton]

Somewhere I seem to recall an example where the author was able to access
some kind of representation of a variable's type and use it to create
another variable of the same type. It may have been in the context of
templates.

Here's why I ask; I have a member field declared like this:

protected:
vector<vector<SbVec3f*> >* strips_ptr;

Within a function, I came across a reason to want a local variable of the
same type. The alternatives are to either use the same long (painful to
type) declaration, or use a typedef. I personally dislike typedefs in most
situations. They seem like just another level of indirection with the
potential to obfuscate and confuse.

OTOH, if I can create a variable in such a way that I can see it's another
instance of one I'm already using, that seems more informative and direct.

 

[Gianni Mariani]

Somewhere I seem to recall an example where the author was able to access
some kind of representation of a variable's type and use it to create
another variable of the same type. It may have been in the context of
templates.

Here's why I ask; I have a member field declared like this:

protected:
vector<vector<SbVec3f*> >* strips_ptr;

Within a function, I came across a reason to want a local variable of the
same type. The alternatives are to either use the same long (painful to
type) declaration, or use a typedef. I personally dislike typedefs in most
situations. They seem like just another level of indirection with the
potential to obfuscate and confuse.

OTOH, if I can create a variable in such a way that I can see it's another
instance of one I'm already using, that seems more informative and direct.

The way to extract a type using standard C++ is by using template
functions. However, gcc does have an extension called "typeof" which
allows you to do type extraction without resorting to complex templates.
typeof is not supported universally.

If you can place your algorithm that needs a local variable of your
particular type in a template function then this is pretty easy.

template <typename T> void func( T input )
{
T local_variable;
}

calling "func( strips_ptr )" gives you that local variable.

 

[Chris \( Val \)]

| Somewhere I seem to recall an example where the author was able to access
| some kind of representation of a variable's type and use it to create
| another variable of the same type. It may have been in the context of
| templates.
|
| Here's why I ask; I have a member field declared like this:
|
| protected:
| vector<vector<SbVec3f*> >* strips_ptr;
|
| Within a function, I came across a reason to want a local variable of the
| same type. The alternatives are to either use the same long (painful to
| type) declaration, or use a typedef. I personally dislike typedefs in most
| situations. They seem like just another level of indirection with the
| potential to obfuscate and confuse.
|
| OTOH, if I can create a variable in such a way that I can see it's another
| instance of one I'm already using, that seems more informative and direct.

I'm not sure that I understand exactly what it is
your asking, however, I have to disagree with you,
that typedef' can obfuscate and confuse - I think
that they are a good thing, and do exactly what they
were intended to do quite nicely.

Cheers.
Chris Val

 

[JKop]

Steven T. Hatton posted:

Within a function, I came across a reason to want a local variable of
the same type. The alternatives are to either use the same long
(painful to type) declaration, or use a typedef. I personally dislike
typedefs in most situations. They seem like just another level of
indirection with the potential to obfuscate and confuse.

typedef
MammalWithFourLegsThatBarksAndWaggsItsTailWhenItsHappyAndLowersItsEarsWhenIt
sSadOrAfraid Dog;


I don't see the problem.


-JKop