tag

#tag

##Syntax A tagStatement is:

tag unionVariableReference , expn

##Description A tag statement is a special-purpose assignment that is used for changing the tag of a union variable.

##Example In this example, the tag field of union variable v is set to be passenger, thereby activating the passenger field of v.

    type vehicleInfo :
        union kind : passenger .. recreational
            label passenger :
                cylinders : 1..16
            label farm :
                farmClass : string ( 10 )
            label : % No fields for "otherwise" clause
        end union
    var v : vehicleInfo
    �
    tag v, passenger        % Activate passenger part

##Details A tag statement is the only way to modify the tag field of a union variable (other than by assigning an entire union value to the union variable).

You cannot access a particular set of fields of a union unless the tag is set to match the corresponding label value.

##See also union.html types.