presto-main/src/main/java/io/prestosql/operator/scalar/RowToJsonCast.java/RowToJsonCast/RowToJsonCast
class RowToJsonCast:    private RowToJsonCast()
    {
        super(OperatorType.CAST,
                ImmutableList.of(
                        // this is technically a recursive constraint for cast, but TypeRegistry.canCast has explicit handling for row to json cast
                        new TypeVariableConstraint("T", false, false, "row", ImmutableSet.of(JSON.getTypeSignature()), ImmutableSet.of())),
                ImmutableList.of(),
                JSON.getTypeSignature(),
                ImmutableList.of(new TypeSignature("T")),
                false);
    }