[fpc-pascal] How do record variants without a field name?

[Ryan Gonzalez]

I posted this to Stack Overflow (
http://stackoverflow.com/questions/36504292/iso-pascal-record-variants-without-a-field-name),
but it hasn't gotten any feedback. So, here I go...

Free Pascal allows you to do this:

type RPoint = Record
  Case Boolean of
    False : (X,Y,Z : Real);
    True : (R,theta,phi : Real);
end;

To construct it, you do:

var p: RPoint;
begin
  p.x := 1;
end.

There's one part I don't understand: what's the purpose of the Case Boolean
part? I understand that you can do case MyVal: Boolean; then MyVal becomes
the field selector. However, what is the purpose when there is no field
selector, just a type?

In addition, the ISO Pascal standard says:

With each variant-part shall be associated a type designated the
selector-type possessed by the variant-part . If the variant-selector of
the variant-part contains a tag-field, or if the case-constant- list of
each variant of the variant-part contains only one case-constant, then the
selector-type shall be denoted by the tag-type, and each variant of the
variant-part shall be associated with those values specified by the
selector-type denoted by the case-constants of the case-constant-list of
the variant . Otherwise, the selector-type possessed by the variant-part
shall be a new ordinal-type that is constructed to possess exactly one
value for each variant of the variant-part, and no others, and each such
variant shall be associated with a distinct value of that type.

I don't quite understand what the selector-type is and why it would be a
new ordinal-type. Wouldn't the selector-type just be the type like in case
Boolean of? And what does each case-constant-list having only one
case-constant have to do with it?

Thanks in advance!

-- 
Ryan
[ERROR]: Your autotools build scripts are 200 lines longer than your
program. Something’s wrong.
http://kirbyfan64.github.io/
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