$stringVar::constant?

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  • Gordon
    #1

    $stringVar::constant?

    I'm trying to get a constant from a class, where the constant's name
    is known, but the class name isn't. I want to do things this way
    because I want classes to be able to define certain aspects for their
    setup themselves.

    For example: I have a situation where I have a script that can deal
    with objects of one of several classes, but each class needs some
    slightly different setup parameters. I'm currently taking care of
    this with a switch statement, but i'd like to eliminate it if at all
    possible. As it stands, my code is along the lines of:

    $thisClass = 'FirstClass'; // Will come from an external source in
    real life, validated of course!

    switch ($thisClass)
    {
    case 'FirstClass' :
    $val = 'first val';
    break;
    case 'SecondClass' :
    $val = 'second val';
    break;
    case 'ThirdClass' :
    $val = 'third val';
    break;
    // ...
    }

    echo ($val);

    I'd rather do something along the lines of

    class FirstClass
    {
    const VAL = 'First val';
    }
    //...

    echo ($thisClass::VA L);

    I'm guessing that there is some function that returns a class from a
    string, but I can't find it. Can anyone help out here?
    Tags: None
    • Jerry Stuckle
      #2
      Re: $stringVar::con stant?

      Gordon wrote:
      I'm trying to get a constant from a class, where the constant's name
      is known, but the class name isn't. I want to do things this way
      because I want classes to be able to define certain aspects for their
      setup themselves.
      >
      For example: I have a situation where I have a script that can deal
      with objects of one of several classes, but each class needs some
      slightly different setup parameters. I'm currently taking care of
      this with a switch statement, but i'd like to eliminate it if at all
      possible. As it stands, my code is along the lines of:
      >
      $thisClass = 'FirstClass'; // Will come from an external source in
      real life, validated of course!
      >
      switch ($thisClass)
      {
      case 'FirstClass' :
      $val = 'first val';
      break;
      case 'SecondClass' :
      $val = 'second val';
      break;
      case 'ThirdClass' :
      $val = 'third val';
      break;
      // ...
      }
      >
      echo ($val);
      >
      I'd rather do something along the lines of
      >
      class FirstClass
      {
      const VAL = 'First val';
      }
      //...
      >
      echo ($thisClass::VA L);
      >
      I'm guessing that there is some function that returns a class from a
      string, but I can't find it. Can anyone help out here?

      Not real nice, but it can be done...

      <?php

      class FirstClass {
      const VAL = 'First val';
      }

      class SecondClass {
      const VAL = 'Second val';
      }

      $cname = 'FirstClass';
      $str = $cname . '::VAL;';
      eval('echo ' . $str . ';');
      echo "\n";

      $cname = 'SecondClass';
      $str = $cname . '::VAL;';
      eval('echo ' . $str . ';');
      echo "\n";

      ?>

      Outputs

      First val
      Second val

      But I don't like it :-)

      --
      =============== ===
      Remove the "x" from my email address
      Jerry Stuckle
      JDS Computer Training Corp.
      jstucklex@attgl obal.net
      =============== ===

        Comment

        • Michael Fesser
          #3
          Re: $stringVar::con stant?

          ..oO(Jerry Stuckle)
          >Gordon wrote:
          >I'm trying to get a constant from a class, where the constant's name
          >is known, but the class name isn't. I want to do things this way
          >because I want classes to be able to define certain aspects for their
          >setup themselves.
          >[...]
          >>
          >echo ($thisClass::VA L);
          >>
          >I'm guessing that there is some function that returns a class from a
          >string, but I can't find it. Can anyone help out here?
          >
          >
          >Not real nice, but it can be done...
          >
          ><?php
          >
          >class FirstClass {
          const VAL = 'First val';
          >}
          >
          >class SecondClass {
          const VAL = 'Second val';
          >}
          >
          >$cname = 'FirstClass';
          >$str = $cname . '::VAL;';
          >eval('echo ' . $str . ';');
          >echo "\n";
          >
          >$cname = 'SecondClass';
          >$str = $cname . '::VAL;';
          >eval('echo ' . $str . ';');
          >echo "\n";
          >
          >?>
          >
          >Outputs
          >
          >First val
          >Second val
          >
          >But I don't like it :-)
          Neither do I. According to the manual this

          echo $thisClass::VAL ;

          should become possible with PHP 5.3. Until then the Reflection API might
          be another option, but I haven't tried it.

          Micha

            Comment

            • Gordon
              #4
              Re: $stringVar::con stant?

              On Jun 28, 3:13 pm, Michael Fesser <neti...@gmx.de wrote:
              .oO(Jerry Stuckle)
              >
              >
              >
              Gordon wrote:
              I'm trying to get a constant from a class, where the constant's name
              is known, but the class name isn't.  I want to do things this way
              because I want classes to be able to define certain aspects for their
              setup themselves.
              [...]
              >
              echo ($thisClass::VA L);
              >
              I'm guessing that there is some function that returns a class from a
              string, but I can't find it.  Can anyone help out here?
              >
              Not real nice, but it can be done...
              >
              <?php
              >
              class FirstClass {
                  const VAL = 'First val';
              }
              >
              class SecondClass {
                  const VAL = 'Second val';
              }
              >
              $cname = 'FirstClass';
              $str = $cname . '::VAL;';
              eval('echo ' . $str . ';');
              echo "\n";
              >
              $cname = 'SecondClass';
              $str = $cname . '::VAL;';
              eval('echo ' . $str . ';');
              echo "\n";
              >
              ?>
              >
              Outputs
              >
              First val
              Second val
              >
              But I don't like it :-)
              >
              Neither do I. According to the manual this
              >
              echo $thisClass::VAL ;
              >
              should become possible with PHP 5.3. Until then the Reflection API might
              be another option, but I haven't tried it.
              >
              Micha
              Thanks. Further investigation turned up the eval() option but I
              really don't like using eval(), especially on user-provided data, even
              if it has been validated. You never know what you might have missed.
              On the other hand reflection might be overkill...

                Comment

                • Charles Calvert
                  #5
                  Re: $stringVar::con stant?

                  On Fri, 27 Jun 2008 09:15:36 -0700 (PDT), Gordon
                  <gordon.mcvey@n tlworld.comwrot e in
                  <de6b1e03-90aa-465f-89f1-6df9019b9ca4@c6 5g2000hsa.googl egroups.com>:
                  >I'm trying to get a constant from a class, where the constant's name
                  >is known, but the class name isn't. I want to do things this way
                  >because I want classes to be able to define certain aspects for their
                  >setup themselves.
                  >
                  >For example: I have a situation where I have a script that can deal
                  >with objects of one of several classes, but each class needs some
                  >slightly different setup parameters. I'm currently taking care of
                  >this with a switch statement, but i'd like to eliminate it if at all
                  >possible. As it stands, my code is along the lines of:
                  >
                  >$thisClass = 'FirstClass'; // Will come from an external source in
                  >real life, validated of course!
                  >
                  >switch ($thisClass)
                  >{
                  case 'FirstClass' :
                  $val = 'first val';
                  break;
                  case 'SecondClass' :
                  $val = 'second val';
                  break;
                  case 'ThirdClass' :
                  $val = 'third val';
                  break;
                  // ...
                  >}
                  >
                  >echo ($val);
                  >
                  >I'd rather do something along the lines of
                  >
                  >class FirstClass
                  >{
                  const VAL = 'First val';
                  >}
                  >//...
                  >
                  >echo ($thisClass::VA L);
                  >
                  >I'm guessing that there is some function that returns a class from a
                  >string, but I can't find it. Can anyone help out here?
                  There are a couple of OO options, assuming that you're using php 5.

                  1. Inheritance. If you can make all of the classes inherit from a
                  base class, make the constant a member of the base class, then
                  override it in the derived classes. You can then access the constant
                  by assigning the instance of the derived class to a variable declared
                  as the base class.

                  2. Interface. If #1 isn't feasible, create an interface that contains
                  the required constant, then make each class implement that interface.
                  You can then access the instance of the class via a variable declared
                  as the interface.

                  See <http://www.php.net/manual/en/language.oop5.c onstants.phpfor
                  more info.

                    Comment

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