Operator.cs:
#    3| [Class] C
#    5|   5: [ImplicitConversionOperator] implicit conversion
#    5|     -1: [TypeMention] C
#-----|     2: (Parameters)
#    5|       0: [Parameter] i
#    5|         -1: [TypeMention] int
#    5|     4: [BlockStmt] {...}
#    5|       0: [ReturnStmt] return ...;
#    5|         0: [NullLiteral] null
#    7|   6: [Field] x1
#    7|     -1: [TypeMention] int
#    8|   7: [Field] x2
#    8|     -1: [TypeMention] C
#   11|   8: [Method] M
#   11|     -1: [TypeMention] Void
#   12|     4: [BlockStmt] {...}
#   13|       0: [ExprStmt] ...;
#   13|         0: [AssignExpr] ... = ...
#   13|           0: [FieldAccess] access to field x2
#   13|           1: [OperatorCall] call to operator implicit conversion
#   13|             0: [FieldAccess] access to field x1