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probably stupid question of the day

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  • Francois Berenger
    Why do we have to provide the type + the comparison fonction when we create a set? Isn t the comparison function the only parameter that should be needed to
    Message 1 of 3 , Jun 5, 2013
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      Why do we have to provide the type + the comparison
      fonction when we create a set?

      Isn't the comparison function the only parameter
      that should be needed to "specialize" a set?
    • Johan Mazel
      Because, you may have a comparison function that do not use every element of the type actually operate the comparison. For example, a record with an index and
      Message 2 of 3 , Jun 9, 2013
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        Because, you may have a comparison function that do not use every element
        of the type actually operate the comparison. For example, a record with an
        index and any kind of data where you want data to be ordered by index..


        2013/6/5 Francois Berenger <berenger@...>

        > **
        >
        >
        > Why do we have to provide the type + the comparison
        > fonction when we create a set?
        >
        > Isn't the comparison function the only parameter
        > that should be needed to "specialize" a set?
        >
        >


        [Non-text portions of this message have been removed]
      • Lukasz Stafiniak
        ... When you apply the functor, you need to specialize the type of elements held in a set. That s because you need to somehow connect the type of the elements
        Message 3 of 3 , Jun 9, 2013
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          On Wed, Jun 5, 2013 at 9:04 AM, Francois Berenger <berenger@...> wrote:

          > **
          >
          >
          > Why do we have to provide the type + the comparison
          > fonction when we create a set?
          >
          > Isn't the comparison function the only parameter
          > that should be needed to "specialize" a set?
          >

          When you apply the functor, you need to specialize the type of elements
          held in a set. That's because you need to somehow connect the type of the
          elements in the set with the type accepted by your comparison function. The
          only other option would be that the comparison function is polymorphic with
          respect to elements it compares, which would be rather useless.


          [Non-text portions of this message have been removed]
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