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good to have typedef?

 
 
doublemaster007@gmail.com
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      10-30-2009
Is it good to typedef the types?? What is the actual use of it? I am
working on project where tooo many typedefs are used..If many people
are working on a project..only the person who defined will be
remembering it..finally too many typedefs will be there and code
becomes hard to use...

So i wanna know..is typedefs are really useful in full fledged
project??
 
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Johannes Schaub (litb)
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      10-30-2009
http://www.velocityreviews.com/forums/(E-Mail Removed) wrote:

> Is it good to typedef the types?? What is the actual use of it? I am
> working on project where tooo many typedefs are used..If many people
> are working on a project..only the person who defined will be
> remembering it..finally too many typedefs will be there and code
> becomes hard to use...
>

Sometimes, you can make better use of identity than of typedef. For example
to make a pointer to an array, and you want to use a typedef, you can
instead use identity

identity<int[5]>::type *ptr;

I've seen that identity has lots of nice uses, where otherwise a typedef
would have to be used to make things easy to read. The above would look like
the below with typedef

typedef int array_type[5];
array_type *ptr;

And i think using identity, this looks and feels better.
 
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Richard
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      10-31-2009
[Please do not mail me a copy of your followup]

"(E-Mail Removed)" <(E-Mail Removed)> spake the secret code
<(E-Mail Removed)> thusly:

>So i wanna know..is typedefs are really useful in full fledged
>project??


Like anything in your code, you should use them if they add value and
avoid them if they are not carrying their weight.

Its possible to overuse typedefs to the point where they fail to
provide value.

For instance, I personally don't find value in typedefs like this:

typedef std::string *stringPtr;

Particularly since using that typedef leads you down the problem of
improperly specifying pointers to const strings. People think its
this:

const stringPtr unchangedStringThroughPointer;

Unfortunately you didn't specify the string was const, but that the
pointer was const. That's why Windows headers have the typedefs LPSTR
and LPCSTR, with the former being pointer to char and the latter being
pointer to const char. (The LP business is just an anachronism from
Win16 days.) Is LPSTR really more clear than char *? Is LPCSTR
really more clear than char const *? I don't think so, but I'll use
those typedefs because they are pervasive in Windows and Windows
programmers are familiar enough with them to know what they mean. I
stop short of using things like LPDIRECT3DDEVICE9 instead of
IDirect3DDevice9 *. The former just feels like screaming to me, while
the latter is easier to read and is just as clear (in context) that
we're talking about a COM interface pointer.

I'm currently working on a code base that is replete with typedefs
like these:

typedef unsigned char uint8;
typedef int int32;
typedef unsigned int uint32;
typedef float real;
typedef double lreal;

and so-on.

Personally I don't like declaring my types as having a bit size unless
it is truly relevant to their role. Once *everything* is declared as
an int32, how do you know which ones *really* need 32-bits and which
ones are comfortable in the native size of int? If you really need to
guarantee that an int is at least 32-bits you can do this in other
ways than polluting the entire source base with spurious int32's
everywhere.

The real/lreal thing is particularly annoying. It just obfuscates the
code in an attemp to abstract away a coupling to an implementation
dependency, yet it fails to do so in any meaningful way because it is
just an alias for an implementation dependency instead of an
abstraction like a new type (i.e. a class) would do. Because the
built-in types like int, float and double can't be extended or
customized, the typedef doesn't carry its own weight. It obscures the
fact that you *are* coupled to the implementation details of a float
or a double, while at the same time pretending to decouple you from
those details. It adds no value and reduces the clarity of the code.

The one area where typedefs are most useful is in consuming template
classes. std::string::find returns std::string::size_type; if I'm
using that type repeatedly in a function its easier to create a local
typedef for it:

void wipeOutSlashes(std::string &text)
{
typedef std::string::size_type size_type;

// declare locals of type size_type
}

That's just a simple example. It gets more useful when declaring
iterators and other types related to a template class. If you are
writing template libraries, creating nested typedefs that refer to
related types in your base class or in the template argument are very
useful for making the template expansion more readable.
--
"The Direct3D Graphics Pipeline" -- DirectX 9 draft available for download
<http://legalizeadulthood.wordpress.com/the-direct3d-graphics-pipeline/>

Legalize Adulthood! <http://legalizeadulthood.wordpress.com>
 
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Saeed Amrollahi
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Posts: n/a
 
      10-31-2009
On Oct 31, 12:01*am, "(E-Mail Removed)"
<(E-Mail Removed)> wrote:
> Is it good to typedef the types?? What is the actual use of it? I am
> working on project where tooo many typedefs are used..If many people
> are working on a project..only the person who defined will be
> remembering it..finally too many typedefs will be there and code
> becomes hard to use...
>
> So i wanna know..is typedefs are really useful in full fledged
> project??


Hi

Just my two cents ...
In addition to what Richard wrote, sometimes typedef declaration is
almost necessary.
For example, in C++ standard library, there are a lot of typedef
declarations
inside declaration/defintion of containers. A typical typedef is a
another
name for template parameter:
template<class T> // the bare bones
class std::list {
// ...
typedef T value_type;
// ...
};
So, we can use the template parameter:
void f(list<T>& L)
{
typename list<T>::value_type v = *v.begin();
// ...
}
without such typedef we can't use template parameter in generic
manner.
Also the keyword "typename" in above line is necessary.

Regards,
-- Saeed Amrollahi
 
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Jorgen Grahn
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      11-04-2009
On Fri, 2009-10-30, (E-Mail Removed) wrote:
> Is it good to typedef the types?? What is the actual use of it? I am
> working on project where tooo many typedefs are used..If many people
> are working on a project..only the person who defined will be
> remembering it..finally too many typedefs will be there and code
> becomes hard to use...


I have to say that doesn't make sense to me. It's hard to see what
the problem is with your code.

> So i wanna know..is typedefs are really useful in full fledged
> project??


I agree with "Richard" elsewhere in this thread. And also:

- Most people, I think, dislike when a typedef is used to try to hide
that something is a struct or a pointer. Like, having to type FooPtr
instead of Foo*. I think Richard mentioned why that is not only
annoying but also harmful.

- Projects often overuse CHAR, UCHAR, uint32, etc ... typedefs.
Not a plain char or int in sight. I hate that.

- Typedefs are just aliases; they don't buy you type safety.
You might have
typedef std::string PersonName;
typedef std::string Gender;
and still mix up the arguments to
void DatingService::add(const PersonName&, const Gender&);
In other words, that prototype adds *no* value compared to
one where the arguments are const std::string&.

Is your problem one of these?

/Jorgen

--
// Jorgen Grahn <grahn@ Oo o. . .
\X/ snipabacken.se> O o .
 
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James Kanze
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      11-05-2009
On Nov 4, 11:06 pm, Andy Champ <(E-Mail Removed)> wrote:
> Jorgen Grahn wrote:


> <snip>> - Projects often overuse CHAR, UCHAR, uint32, etc ... typedefs.
> > Not a plain char or int in sight. I hate that.


> </snip>


> We've got an awful lot of uint32_t in our project. That's
> because it represents a data item which, because of published
> specifications, is 32 bits, no more, no less.


I'm curious. What published specifications impose anything
concerning the internal representation? (Externally, of course,
the published specifications probably impose more than just 32
bits. Like byte order, for example.)

> int is a word size which is convenient for the machine - good
> for loopcounts, but not for precise data mappings.


That's not it's role. When you need to input or output data in
a precise format, you write code to do so: int32_t and others
aren't directly applicable here. (Indirectly... if you're
willing to restrict your portability to machines where uint32_t
is available---and that's still a lot of them---, then using it
for certain intermediate representations can make your code
significantly simpler.)

--
James Kanze
 
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Nick Keighley
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      11-05-2009
On 4 Nov, 22:19, Jorgen Grahn <(E-Mail Removed)> wrote:
> On Fri, 2009-10-30, (E-Mail Removed) wrote:


> > Is it good to typedef the types?? What is the actual use of it? I am
> > working on project where tooo many typedefs are used..If many people
> > are working on a project..only the person who defined will be
> > remembering it..finally too many typedefs will be there and code
> > becomes hard to use...


get a decent source browser. I agree typedefs can be over-used but the
they can be under-used as well.

<snip>

> - Most people, I think, dislike when a typedef is used to try to hide
> * that something is a struct or a pointer.


I've no objection to hiding a struct behind a typedef (or at least in
C becasue I hate scattering the "struct" keyword all over the place
(I'm aware C++ doesn't have this problem)). I'm almost with you on
pointers except I justify hungarian for smart pointers. This is one of
the few places I'd advocate hungarian because I /want/ my nose rubbed
in what-type-of-pointer is this to make sure I cleanup properly.


> Like, having to type FooPtr
> * instead of Foo*. I think Richard mentioned why that is not only
> * annoying but also harmful.


oh, I agree. Then there's hiding arrays (but C++ programmers don't use
arrays )


> - Projects often overuse CHAR, UCHAR, uint32, etc ... typedefs.
> * Not a plain char or int in sight. I hate that.


yuk. I've worked on projects where the programmming standards said you
must not use raw types. And the configuration control system
checked.

Lovely bug:-

Station_id read_station_id (FILE *in)
{
Station_id station_id;
fscanf (in, "%d", &station_id);
return station_id;
}

Station_id was a short.


> - Typedefs are just aliases; they don't buy you type safety.


too true. Possibly one of C's design mistakes.

> * You might have
> * * *typedef std::string PersonName;
> * * *typedef std::string Gender;
> * and still mix up the arguments to
> * * *void DatingService::add(const PersonName&, const Gender&);
> * In other words, that prototype adds *no* value compared to
> * one where the arguments are const std::string&.


it documents intent. I'd maybe write

void DatingService::add(const std::string &personName&, std::const
string& gender);


> Is your problem one of these?

 
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James Kanze
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      11-05-2009
On Nov 5, 9:31 pm, Andy Champ <(E-Mail Removed)> wrote:
> James Kanze wrote:


> > I'm curious. What published specifications impose anything
> > concerning the internal representation? (Externally, of
> > course, the published specifications probably impose more
> > than just 32 bits. Like byte order, for example.)


> >> int is a word size which is convenient for the machine -
> >> good for loopcounts, but not for precise data mappings.


> > That's not it's role. When you need to input or output data
> > in a precise format, you write code to do so: int32_t and
> > others aren't directly applicable here. (Indirectly... if
> > you're willing to restrict your portability to machines
> > where uint32_t is available---and that's still a lot of
> > them---, then using it for certain intermediate
> > representations can make your code significantly simpler.)


> You've answered your own question - it's a data transfer
> specification.


In which case, uint32_t doesn't necessarily buy you that much.
(It does restrict portability, however, since it is guaranteed
not to be available on some machines.)

--
James Kanze
 
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James Kanze
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      11-05-2009
On Nov 5, 10:57 am, Nick Keighley <(E-Mail Removed)>
wrote:
> On 4 Nov, 22:19, Jorgen Grahn <(E-Mail Removed)> wrote:


[...]
> > You might have
> > typedef std::string PersonName;
> > typedef std::string Gender;
> > and still mix up the arguments to
> > void DatingService::add(const PersonName&, const Gender&);
> > In other words, that prototype adds *no* value compared to
> > one where the arguments are const std::string&.


> it documents intent. I'd maybe write


> void DatingService::add(const std::string &personName&, std::const
> string& gender);


Why not:

void DatingService::add( Name const& personName,
Gender const& gender );

A Name is more than a string, and a Gender is most likely an
enum.

--
James Kanze
 
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Ian Collins
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      11-06-2009
Andy Champ wrote:
> James Kanze wrote:
>>
>> In which case, uint32_t doesn't necessarily buy you that much.
>> (It does restrict portability, however, since it is guaranteed
>> not to be available on some machines.)

>
> Luckily for _me_ I only need to worry about Windoze boxes - albeit 64
> bit is likely to come up soon. And I'm also lucky that my byte order
> matches the spec. - not everyone does the ISO 9660 trick of storing a
> number in both common orders, it's not space efficient!
>
> But what should I use if I want to represent a guaranteed-to-be-32-bit
> quantity?


uint32_t if the system has it. If not, define your own.

--
Ian Collins
 
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