difference between generics and templates

[Anton Berg]

Hi,

I suppose this question was already often asked and in fact I am not
interested in a complete overview of the differences, cause I already
found them on several pages.

In fact, what I want to know is the following. What is meant by:
"Here's a subtle point, but it's a direct result of how types are
identified in .NET. Let's say that C++ code in assembly A has used a
List<int> template specialization and that C++ code in assembly B
expects to use that exact same specialized type. Code in assembly A
creates an instance of the List<int> type and passes a reference to that
instance to code in assembly B that wishes to use its List<int> type.
Boom! At the very least, you will get a runtime type mismatch exception.
Depending on how you pass the reference, you might even get the error at
compile time. The error is because the List<int> type in assembly A is
not the same type as List<int> in assembly B."
(Taken from:
http://www.developer.com/net/cplus/a...919_3367531_1).

What does the author means by assembly? Is this a class?

So far, I understand this, the following is not possible with templates:
class A
{
public std::vector<int> myVector;

public A(std::vector<int> _myVector)
{
// do something
}
}

class B
{
public std::vector<int> myVector;
public A _a;

public B() : myVector()
{
_a = new A(myVector);
}
}

(code is not compiled!)

Is this the problem described above, or what does the author means?

Thanks for your help!
Anton

[puzzlecracker]

Anton Berg wrote:

Hi,

I suppose this question was already often asked and in fact I am not
interested in a complete overview of the differences, cause I already
found them on several pages.

In fact, what I want to know is the following. What is meant by:
"Here's a subtle point, but it's a direct result of how types are
identified in .NET. Let's say that C++ code in assembly A has used a
List<int> template specialization and that C++ code in assembly B
expects to use that exact same specialized type. Code in assembly A
creates an instance of the List<int> type and passes a reference to that
instance to code in assembly B that wishes to use its List<int> type.
Boom! At the very least, you will get a runtime type mismatch exception.
Depending on how you pass the reference, you might even get the error at
compile time. The error is because the List<int> type in assembly A is
not the same type as List<int> in assembly B."
(Taken from:
http://www.developer.com/net/cplus/a...919_3367531_1).

What does the author means by assembly? Is this a class?

So far, I understand this, the following is not possible with templates:
class A
{
public std::vector<int> myVector;

public A(std::vector<int> _myVector)
{
// do something
}
}

class B
{
public std::vector<int> myVector;
public A _a;

public B() : myVector()
{
_a = new A(myVector);
}
}

(code is not compiled!)

Is this the problem described above, or what does the author means?

Thanks for your help!
Anton

It was never answered b/c it is OT - off-topic in this group! Try
comp.compilers.javacc

[Victor Bazarov]

Anton Berg wrote:

I suppose this question was already often asked and in fact I am not
interested in a complete overview of the differences, cause I already
found them on several pages.

In fact, what I want to know is the following. What is meant by:
"Here's a subtle point, but it's a direct result of how types are
identified in .NET.
..NET is its own universe and it has some areas that do not intersect with
our, Standard C++, universe. You should consider asking in a .NET forum
about .NET-specific things.
Let's say that C++ code in assembly A has [...]"
(Taken from:
http://www.developer.com/net/cplus/a...919_3367531_1).

What does the author means by assembly? Is this a class?
No.

So far, I understand this, the following is not possible with templates:
class A
{
public std::vector<int> myVector;

public A(std::vector<int> _myVector)
{
// do something
}
}

class B
{
public std::vector<int> myVector;
public A _a;

public B() : myVector()
{
_a = new A(myVector);
}
}

(code is not compiled!)
Nor will it. It's not C++.
Is this the problem described above, or what does the author means?

You need to ask in a newsgroup dedicated to the language in which your
code is written.

V

[Anton Berg]

So far, I understand this, the following is not possible with templates:
class A
{
public std::vector<int> myVector;

public A(std::vector<int> _myVector)
{
// do something
}
}

class B
{
public std::vector<int> myVector;
public A _a;

public B() : myVector()
{
_a = new A(myVector);
}
}

(code is not compiled!)

Nor will it. It's not C++.

What's the problem with the code? Maybe I did too much java the last
days... but it looks to me like a correc code snipplet for c++.

[Bo Persson]

"Anton Berg" <no****@gmx.de> skrev i meddelandet
news:dq**********@online.de...

So far, I understand this, the following is not possible with
templates:
class A
{
public std::vector<int> myVector;

public A(std::vector<int> _myVector)
{
// do something
}
}

class B
{
public std::vector<int> myVector;
public A _a;

public B() : myVector()
{
_a = new A(myVector);
}
}

(code is not compiled!)

Nor will it. It's not C++.

What's the problem with the code? Maybe I did too much java the last
days... but it looks to me like a correc code snipplet for c++.

But is it ISO C++ (no), or C++/CLI (perhaps)?

Two totally different languages.
Bo Persson

[Thomas J. Gritzan]

Anton Berg schrieb:

So far, I understand this, the following is not possible with templates:
class A
{
public std::vector<int> myVector;
should be:

public:
std::vector<int> myVector;
public A(std::vector<int> _myVector)
public:
A(std::vector<int> myVector_)
{
// do something
}
}
Expecting ';'
class B
{
public std::vector<int> myVector;
public A _a;
see above.
public B() : myVector()
{
_a = new A(myVector);
_a is no pointer.
}
}
;
(code is not compiled!)

Nor will it. It's not C++.

What's the problem with the code? Maybe I did too much java the last
days... but it looks to me like a correc code snipplet for c++.

Is it Java? no! Is it C++? no!

Thomas

[Anton Berg]

Hi,

Thomas J. Gritzan wrote:

Anton Berg schrieb:
Is it Java? no! Is it C++? no!

Ok, sorry! I totally mixed it. Sorry for that and thanks for the hints!

[Victor Bazarov]

Anton Berg wrote:

So far, I understand this, the following is not possible with templates:
class A
{
public std::vector<int> myVector;

public A(std::vector<int> _myVector)
{
// do something
}
}

class B
{
public std::vector<int> myVector;
public A _a;

public B() : myVector()
{
_a = new A(myVector);
}
}

(code is not compiled!)

Nor will it. It's not C++.

What's the problem with the code?

"public" doesn't have a colon after it. The class definition does not
have a semicolon after it. The result obtained from a 'new' expression
has a pointer type and usually cannot be assigned to an object (_a). I
honestly thought you confused this NG as also a place for C#.
Maybe I did too much java the last
days... but it looks to me like a correc code snipplet for c++.

Well, if you have no doubt, you should. It does look like you did just
a bit too much Java. If you have doubt, always try to compile it before
posting, otherwise you cast shadow on your post. Your code, rewritten:

class A
{
std::vector<int> myVector;
public:
A(std::vector<int> const & _myVector) : myVector(_myVector)
{
}
};

class B
{
std::vector<int> myVector;
A _a;
public:
B() : myVector(), _a(myVector)
{
}
};

And, _yes_, it is perfectly OK, which then brings me to this statement:
I do not understand what you mean "not possible with templates".

V

[Anton Berg]

Hi Victor,

What's the problem with the code?
"public" doesn't have a colon after it. The class definition does not
have a semicolon after it. The result obtained from a 'new' expression
has a pointer type and usually cannot be assigned to an object (_a). I
honestly thought you confused this NG as also a place for C#.

Sorry, for the confussion. Last days I did tooooooo much java, sadly.
And it seems, I was totally too fast with my posting. Sorry for that!

class A
{
std::vector<int> myVector;
public:
A(std::vector<int> const & _myVector) : myVector(_myVector)
{
}
};

class B
{
std::vector<int> myVector;
A _a;
public:
B() : myVector(), _a(myVector)
{
}
};

And, _yes_, it is perfectly OK, which then brings me to this statement:
I do not understand what you mean "not possible with templates".

Thanks for rewritting my code! I am really sad, that I started to forget
the lovely C++ language...

So, in the article, I mentioned, there the author said, that if I
instantiate a template class in two different assemblys, then I get a
compilation error; that I meant with "not possible". I thought that
assembly is a c++ term I maybe missed or is new to the language (I
didn't do any enhanced c++ stuff for almost 2 years).

Thanks for your help!

[Martin Eisenberg]

Anton Berg wrote:

So, in the article, I mentioned, there the author said, that if
I instantiate a template class in two different assemblys, then
I get a compilation error; that I meant with "not possible". I
thought that assembly is a c++ term I maybe missed or is new to
the language (I didn't do any enhanced c++ stuff for almost 2
years).

I think that by "assembly" the author means "a file containing object
code", i.e., an executable, object, or library file. The point of the
quote you gave is that two such files may have been compiled using
different standard library implementations so that their respective
sources name totally unrelated structures by the same "list<int>"
token sequence. Consequently, linking the modules together such that
one module tries to access an object the other created through a
declaration of its own makes no sense.
Martin

--
Quidquid latine scriptum sit, altum viditur.