OOP casting classes (using one single variable for similar types of classes)

Discussion in 'C++' started by roberts.noah@gmail.com, Jan 6, 2006.

  1. Guest

    Michael wrote:

    > Isn't it possible to check the audio format of the incoming audio material
    > at first and then casting the IN and OUT variable to the proper type of
    > audio class?


    You might consider the "factory method" or "abstract factory" design
    patterns.
     
    , Jan 6, 2006
    #1
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  2. Michael Guest

    Hi,

    I think my problem deals with class casting and inheritance.

    I want to deal with various Audio Formats, reading into memory for
    modification, working with it (done by different classes), and writing the
    result to disk afterwards.

    Therefore I have created some classes, e.g. WaveFileIO and AiffFileIO and
    MP3FileIO and AuFileIO for the In/Out operations.
    They all are inherited from the AudioFileIO class, because they all share
    common methods like readSamples, writeSamples, readHeader, writeHeader.
    Only the implementation is sometimes different.

    Now, I want to use them in a let's say generic way:

    [1]
    while(there is data)
    {
    IN.readSamples(); // using the classes mentioned above

    DelayEffect.work(); // modify the memory buffer(sample data)

    OUT.writeSamples(); // using the classes mentioned above
    }

    But due to different audio formats, the type of the IN and OUT variable
    depends on the desired audio format the user specifies.
    I do not want to code every time many IF-THEN-ELSE statements for checking
    the desired format and for using the proper variable.

    Isn't it possible to check the audio format of the incoming audio material
    at first and then casting the IN and OUT variable to the proper type of
    audio class?
    Like:

    IF the incoming file is a WAV, then IN = Type of WaveFileIO
    ELSE IF incoming file is a AIF, then IN = Type of AiffFileIO

    // then using the code fragment [1], and other code fragments like [1]


    Ciao, Michael
     
    Michael, Jan 6, 2006
    #2
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  3. Re: OOP casting classes (using one single variable for similar typesof classes)

    Michael wrote:
    > I think my problem deals with class casting and inheritance.
    >
    > I want to deal with various Audio Formats, reading into memory for
    > modification, working with it (done by different classes), and writing the
    > result to disk afterwards.
    >
    > Therefore I have created some classes, e.g. WaveFileIO and AiffFileIO and
    > MP3FileIO and AuFileIO for the In/Out operations.
    > They all are inherited from the AudioFileIO class, because they all share
    > common methods like readSamples, writeSamples, readHeader, writeHeader.
    > Only the implementation is sometimes different.
    >
    > Now, I want to use them in a let's say generic way:
    >
    > [1]
    > while(there is data)
    > {
    > IN.readSamples(); // using the classes mentioned above
    >
    > DelayEffect.work(); // modify the memory buffer(sample data)
    >
    > OUT.writeSamples(); // using the classes mentioned above
    > }
    >
    > But due to different audio formats, the type of the IN and OUT variable
    > depends on the desired audio format the user specifies.
    > I do not want to code every time many IF-THEN-ELSE statements for checking
    > the desired format and for using the proper variable.
    >
    > Isn't it possible to check the audio format of the incoming audio material
    > at first and then casting the IN and OUT variable to the proper type of
    > audio class?
    > Like:
    >
    > IF the incoming file is a WAV, then IN = Type of WaveFileIO
    > ELSE IF incoming file is a AIF, then IN = Type of AiffFileIO
    >
    > // then using the code fragment [1], and other code fragments like [1]


    Your problem is in the incomplete design.

    Apparently, all "Audio Formats" should derive from a common base class,
    which should have the 'readSamples', 'writeSamples', and other functions
    and you should be instantiating proper derived class object into a pointer
    to the base class:

    AudioFileIO *IN = 0;
    switch (in_file_type) {
    case WAVE: IN = new WaveFileIO(???);
    break;
    case AIFF: IN = new AiffFileIO(???);
    break;
    ...
    }

    // similar for 'OUT'

    Then you should use your 'IN' and 'OUT' pointers _polymorphically_. Read
    about polymorphism, inheritance, abstract base classes, etc.. That's what
    makes C++ well-suited for OOP -- class hierarchies.

    Come back when you redesign your application with polymorphism in place.

    V
     
    Victor Bazarov, Jan 6, 2006
    #3
  4. Guest

    q
     
    , Jan 7, 2006
    #4
  5. Guest

    q
     
    , Jan 7, 2006
    #5
  6. Victor Bazarov wrote:

    > AudioFileIO *IN = 0;
    > switch (in_file_type) {
    > case WAVE: IN = new WaveFileIO(???);
    > break;
    > case AIFF: IN = new AiffFileIO(???);
    > break;
    > ...
    > }
    >


    Bad idea, I think that astract factory pattern is in place......
     
    puzzlecracker, Jan 7, 2006
    #6
  7. Jim Langston Guest

    "Michael" <-chemnitz.de> wrote in message
    news:dpmk66$prc$-chemnitz.de...
    > Hi,
    >
    > I think my problem deals with class casting and inheritance.
    >
    > I want to deal with various Audio Formats, reading into memory for
    > modification, working with it (done by different classes), and writing the
    > result to disk afterwards.
    >
    > Therefore I have created some classes, e.g. WaveFileIO and AiffFileIO and
    > MP3FileIO and AuFileIO for the In/Out operations.
    > They all are inherited from the AudioFileIO class, because they all share
    > common methods like readSamples, writeSamples, readHeader, writeHeader.
    > Only the implementation is sometimes different.
    >
    > Now, I want to use them in a let's say generic way:
    >
    > [1]
    > while(there is data)
    > {
    > IN.readSamples(); // using the classes mentioned above
    >
    > DelayEffect.work(); // modify the memory buffer(sample data)
    >
    > OUT.writeSamples(); // using the classes mentioned above
    > }
    >
    > But due to different audio formats, the type of the IN and OUT variable
    > depends on the desired audio format the user specifies.
    > I do not want to code every time many IF-THEN-ELSE statements for checking
    > the desired format and for using the proper variable.


    What, exactly, do you mean "the type of the IN and OUT variable depends on
    the desired audio format the user specifies." Why isn't the IN and OUT
    variables members of the audio formats themselves? Why aren't they just
    functions? Why do they depend on the type of the desired audio format?
    Where do IN and OUT get their data to work on?

    It sounds like you just need polymorphism, but it could also be that you
    need RTTI. I don't understand what you are trying to do in your code
    snippet. You don't specify what type IN and OUT can be nor why you need
    them.

    I'm sure there's many ways to do what you want, but I don't understand what
    it is you're trying to do.

    >
    > Isn't it possible to check the audio format of the incoming audio material
    > at first and then casting the IN and OUT variable to the proper type of
    > audio class?
    > Like:
    >
    > IF the incoming file is a WAV, then IN = Type of WaveFileIO
    > ELSE IF incoming file is a AIF, then IN = Type of AiffFileIO


    Using RTTI you can check the type of a polymorphic variable. But is this
    what you are really needing to do? I'm just not sure.

    In case you are, though, it would something like this:

    if ( typeid( MyVar ) == typeid( MyClass ) )

    so, for instance, if your polymorphic variable was stored in the variable
    format it would be:

    if ( typeid( Format ) == typeid( WaveFileIO ) )

    although it might be a differernt if Format is a pointer. I *think* this
    syntax is what you need (not positive)

    if ( typeid( Format ) == typeid( WaveFileIO* ) )

    >
    > // then using the code fragment [1], and other code fragments like [1]
    >
    >
    > Ciao, Michael
     
    Jim Langston, Jan 7, 2006
    #7
  8. On Fri, 6 Jan 2006 21:38:10 +0100, "Michael" <-chemnitz.de>
    wrote:

    >Hi,
    >
    >I think my problem deals with class casting and inheritance.


    Virtual functions sounds like the way to go.

    >I want to deal with various Audio Formats, reading into memory for
    >modification, working with it (done by different classes), and writing the
    >result to disk afterwards.
    >
    >Therefore I have created some classes, e.g. WaveFileIO and AiffFileIO and
    >MP3FileIO and AuFileIO for the In/Out operations.
    >They all are inherited from the AudioFileIO class, because they all share
    >common methods like readSamples, writeSamples, readHeader, writeHeader.
    >Only the implementation is sometimes different.
    >
    >Now, I want to use them in a let's say generic way:
    >
    >[1]
    >while(there is data)
    >{
    > IN.readSamples(); // using the classes mentioned above
    >
    > DelayEffect.work(); // modify the memory buffer(sample data)
    >
    > OUT.writeSamples(); // using the classes mentioned above
    >}
    >
    >But due to different audio formats, the type of the IN and OUT variable
    >depends on the desired audio format the user specifies.
    >I do not want to code every time many IF-THEN-ELSE statements for checking
    >the desired format and for using the proper variable.
    >
    >Isn't it possible to check the audio format of the incoming audio material
    >at first and then casting the IN and OUT variable to the proper type of
    >audio class?
    >Like:
    >
    >IF the incoming file is a WAV, then IN = Type of WaveFileIO
    >ELSE IF incoming file is a AIF, then IN = Type of AiffFileIO
    >
    >// then using the code fragment [1], and other code fragments like [1]
    >
    >
    >Ciao, Michael
    >


    In addition to the Abstract Factory design pattern, the Strategy
    pattern might serve you well for this.

    --
    Bob Hairgrove
     
    Bob Hairgrove, Jan 7, 2006
    #8
  9. puzzlecracker wrote:
    > Victor Bazarov wrote:
    >
    >> AudioFileIO *IN = 0;
    >> switch (in_file_type) {
    >> case WAVE: IN = new WaveFileIO(???);
    >> break;
    >> case AIFF: IN = new AiffFileIO(???);
    >> break;
    >> ...
    >> }
    >>

    >
    > Bad idea, I think that astract factory pattern is in place......


    And inside that "abstract factory", what are you going to do? And if
    that factory is abstract, how do you instantiate it? Through another
    abstract factory? Think before you post your "bad idea" replies.
     
    Victor Bazarov, Jan 7, 2006
    #9
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