presto-main/src/main/java/io/prestosql/metadata/PolymorphicScalarFunctionBuilder.java/PolymorphicScalarFunctionBuilder/constant
class PolymorphicScalarFunctionBuilder:    public static <T> Function<SpecializeContext, List<Object>> constant(T value)
    {
        return context -> ImmutableList.of(value);
    }