x.sin() versus sin(x)

Discussion in 'C++' started by franky.backeljauw@ua.ac.be, Sep 8, 2003.

  1. Guest

    Hello,

    I have the following code:

    <code>
    class X {
    ___ sin();
    }

    X sin( X ) { return sin( y, x ); }
    </code>

    Then what should X::sin() do and return? Should it do the same, that is
    sin( y, x ) and return y, or should it do sin( x, x ), that is compute the
    sine of itself and store it in itself?

    I am stuck in choosing either of these, so I would like to know your
    opinion on this, and/or some examples of classes which have both these
    functionalities.

    Thanks in advance for any reply.

    Regards,

    Franky B.
    , Sep 8, 2003
    #1
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  2. Dan Cernat Guest

    wrote in message news:<>...
    > Hello,
    >
    > I have the following code:
    >
    > <code>
    > class X {
    > ___ sin();
    > }
    >
    > X sin( X ) { return sin( y, x ); }
    > </code>
    >
    > Then what should X::sin() do and return? Should it do the same, that is
    > sin( y, x ) and return y, or should it do sin( x, x ), that is compute the
    > sine of itself and store it in itself?
    >
    > I am stuck in choosing either of these, so I would like to know your
    > opinion on this, and/or some examples of classes which have both these
    > functionalities.
    >
    > Thanks in advance for any reply.
    >
    > Regards,
    >
    > Franky B.



    Your code isn't compilable. I cannot even understand what you ask.
    What is sin(y, x)? Never heared of a sine that has two arguments.
    Moreover, why reinventing the wheel? The standard libraries come with
    a sin function. Please clarify.
    Dan Cernat, Sep 8, 2003
    #2
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  3. Howard Guest

    The sin function should *return* its result, not store it in an output
    parameter. It should be defined something like this:

    float sin( float x );

    or

    double sin( double x );


    I see no reason it should be a member of a class, either. The sin function
    operates on a single value and returns a single value, so there's no reason
    to have it a class member. But if, for some reason, you needed such a
    function, then it should still return the result, not store it in a
    parameter.

    -Howard

    P.S., what's with the three leading underscores before the function name?
    And where's the return type?
    Howard, Sep 8, 2003
    #3
  4. Guest

    On Mon, 8 Sep 2003, Dan Cernat wrote:

    > > I have the following code:
    > >
    > > <code>
    > > class X {
    > > ___ sin();
    > > }
    > >
    > > X sin( X ) { X y; sin( y, x ); return y; }
    > > </code>

    >
    > Your code isn't compilable. I cannot even understand what you ask.
    > What is sin(y, x)? Never heared of a sine that has two arguments.
    > Moreover, why reinventing the wheel? The standard libraries come with
    > a sin function. Please clarify.


    The function sin( y, x ) computes the sine of x and stores the result in
    y. Indeed, the code seems to be wrong; I corrected it above. That is,
    the function outside the class is to be used as in y = sin(x).

    The question is what the function X::sin() should do when it occurs in the
    class as given in the example. More precisely, should x.sin() compute the
    sine of x and store the result back into x, or should it behave as y =
    sin(x), that is x.sin() computes the sine of x and returns the result as a
    new object of class X?

    My apologies for the apparant mistake.

    Thanks for any reply.

    Regards,

    Franky B.
    , Sep 8, 2003
    #4
  5. Guest

    On Mon, 8 Sep 2003, Howard wrote:

    > The sin function should *return* its result, not store it in an output
    > parameter. It should be defined something like this:
    >
    > float sin( float x ); or double sin( double x );
    >
    > I see no reason it should be a member of a class, either. The sin function
    > operates on a single value and returns a single value, so there's no reason
    > to have it a class member. But if, for some reason, you needed such a
    > function, then it should still return the result, not store it in a
    > parameter.


    It feels strange, I know, but now I have a class which provides these
    functions as member functions, and also as non-member functions. While
    the non-member function behaves as in y = sin(x), that is it computes the
    sine of x and returns the result (so it can be assigned to y), I thought
    the member function would behave as in x = x.sin(), that is computing the
    sine of the object and storing the result back in x. Otherwise, I would
    see no reason to have these member functions at all.

    > P.S., what's with the three leading underscores before the function
    > name? And where's the return type?


    That depends on what it should do. It is either X& or void, depending on
    whether it should return the result or not (I believe it should not return
    the result if the behavior is as in x = sin(x)).

    Regards,

    Franky B.
    , Sep 8, 2003
    #5
  6. Howard Guest

    >
    > It feels strange, I know, but now I have a class which provides these
    > functions as member functions, and also as non-member functions. While
    > the non-member function behaves as in y = sin(x), that is it computes the
    > sine of x and returns the result (so it can be assigned to y), I thought
    > the member function would behave as in x = x.sin(), that is computing the
    > sine of the object and storing the result back in x. Otherwise, I would
    > see no reason to have these member functions at all.
    >
    > > P.S., what's with the three leading underscores before the function
    > > name? And where's the return type?

    >
    > That depends on what it should do. It is either X& or void, depending on
    > whether it should return the result or not (I believe it should not return
    > the result if the behavior is as in x = sin(x)).
    >

    I cannot imagine when you would ever write "x = sin(x)". The input
    parameter is a value in degreees or radians, and the output is a value
    between -1 and 1.

    If you have some legitimate reason to modify x itself by computing its sine,
    then feel free to do so. As to whether such a function should return a copy
    of x or simply modify x, it all depends on how you intend to use it. If
    you're going to want to write it as part of a longer equation (assignment
    statement), such as "y = 3 * sin(x)", then you'll obviously want it to
    return a useable value.

    If you're *never* going to want to do that, then you can just as easily have
    a void return type and modify the object in place. But in that case, you
    might want to change the name from "sin" to "ConvertToSine" or something
    similar, since using the name "sin" implies the usual mathematical function,
    not a procedural call.

    -Howard
    Howard, Sep 8, 2003
    #6
  7. franky backeljauw wrote:

    > I have the following code:
    >
    > <code>
    > class X {
    > X sin(void) const;
    > };
    >
    > X sin(const X& x) { return sin(y, x); }
    > </code>
    >
    > Then what should X::sin(void) const do and return? Should it do the same
    > that is sin(y, x) and return y, or should it do sin(x, x)
    > that is compute the sine of itself and store it in itself?
    >
    > I am stuck in choosing either of these
    > so I would like to know your opinion on this
    > and/or some examples of classes which have both these functionalities.


    const X x;
    assert(x.sin() == sin(x); // always true
    E. Robert Tisdale, Sep 8, 2003
    #7
  8. tom_usenet Guest

    On Mon, 8 Sep 2003 20:50:11 +0200, wrote:

    >On Mon, 8 Sep 2003, Howard wrote:
    >
    >> The sin function should *return* its result, not store it in an output
    >> parameter. It should be defined something like this:
    >>
    >> float sin( float x ); or double sin( double x );
    >>
    >> I see no reason it should be a member of a class, either. The sin function
    >> operates on a single value and returns a single value, so there's no reason
    >> to have it a class member. But if, for some reason, you needed such a
    >> function, then it should still return the result, not store it in a
    >> parameter.

    >
    >It feels strange, I know, but now I have a class which provides these
    >functions as member functions, and also as non-member functions. While
    >the non-member function behaves as in y = sin(x), that is it computes the
    >sine of x and returns the result (so it can be assigned to y), I thought
    >the member function would behave as in x = x.sin(), that is computing the
    >sine of the object and storing the result back in x. Otherwise, I would
    >see no reason to have these member functions at all.


    Right, drop the member functions (making the non-members friends if
    necessary).

    >
    >> P.S., what's with the three leading underscores before the function
    >> name? And where's the return type?

    >
    >That depends on what it should do. It is either X& or void, depending on
    >whether it should return the result or not (I believe it should not return
    >the result if the behavior is as in x = sin(x)).


    I presume you mean "X or void", not "X& or void".

    It would be counter-intuitive to have sin be a member function that
    modifies the "this" pointer. The intuitive version is a non-member
    that returns the sine of the argument.

    Tom
    tom_usenet, Sep 9, 2003
    #8
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