Examining Variables in a Class or Instance

Gamma: Version 4.0
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# 10.3. Examining Variables in a Class or Instance

Classes and instances can be examined in two ways. For a class, you can simply type the name at the prompt. Instances of classes bound to C structures can be viewed using the `instance_vars` function. To examine an instance of a class, simply type an expression which evaluates to that instance ( see, for example, `elephant` as an instance of the `animal` class in the Instances section of the Class chapter).

You can examine not only user-defined classes, but also the classes which are implemented in Gamma. For example,

        Gamma> PhImage;
        # < Binary Class: PhImage >
        Gamma> instance_vars (PhImage);
        [bpl colors flags format image image_tag palette palette_tag size \
         type xscale yscale]
        Gamma> x = new (PhImage);
        {PhImage (bpl . 0) (colors . 0) (flags . 0) (format . 0) \
         (image . #{}) (image_tag . 0) (palette . []) (palette_tag . 0) \
         (size . {PhDim (h . 0) (w . 0)}) (type . 0) (xscale . 0) \
         (yscale . 0)}
        Gamma> x;
        {PhImage (bpl . 0) (colors . 0) (flags . 0) (format . 0) \
         (image . #{})(image_tag . 0) (palette . []) (palette_tag . 0) \
         (size . {PhDim (h . 0) (w . 0)}) (type . 0) (xscale . 0) \
         (yscale . 0)}
        Gamma> instance_vars (x);
        [(bpl . 0) (colors . 0) (flags . 0) (format . 0) (image . #{}) \
         (image_tag . 0) (palette . []) (palette_tag . 0) (size . \
        {PhDim (h . 0) (w . 0)}) (type . 0) (xscale . 0) (yscale . 0)]
        Gamma> pretty_princ (x, "\n");
        {PhImage (bpl . 0) (colors . 0) (flags . 0) (format . 0) (image . #{} ))
          (image_tag . 0) (palette . []) (palette_tag . 0) \
          (size . {PhDim (h . 0) (w . 0)}) (type . 0) (xscale . 0) \
          (yscale . 0)}
        t

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