When automatically encoding/decoding open types values, how does the decoder determine the type of the open type value?

The decoder determines the type of an open type value from the component relation constraint information. For example, if you have the ASN.1 syntax:

...
Foo ::= SEQUENCE {
   type TYPE-IDENTIFIER.&Id ({ObjSet}),
   value TYPE-IDENTIFIER.&Type ({ObjSet}{@type})
}

ObjSet ::= {
   {IA5String IDENTIFIED BY {1 2 3 4 5}} |
   {BOOLEAN IDENTIFIED BY {1 2 5 } |
   {INTEGER IDENTIFIED BY {2 1 2 2 4 1 6 },
   ...
}

then the decoder knows that it should get the value in the type field and use it to do a lookup in the id column of ObjSet (TYPE-IDENTIFIER is defined in Rec. ITU-T X.681 Annex A), and if the value is found, it sets the type identified in the Type column as the type of the open type value.

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