presto-main/src/main/java/io/prestosql/operator/scalar/MapFilterFunction.java/MapFilterFunction/MapFilterFunction
class MapFilterFunction:    private MapFilterFunction()
    {
        super(new FunctionMetadata(
                new Signature(
                        "map_filter",
                        ImmutableList.of(typeVariable("K"), typeVariable("V")),
                        ImmutableList.of(),
                        mapType(new TypeSignature("K"), new TypeSignature("V")),
                        ImmutableList.of(
                                mapType(new TypeSignature("K"), new TypeSignature("V")),
                                functionType(new TypeSignature("K"), new TypeSignature("V"), BOOLEAN.getTypeSignature())),
                        false),
                false,
                ImmutableList.of(
                        new FunctionArgumentDefinition(false),
                        new FunctionArgumentDefinition(false)),
                false,
                false,
                "return map containing entries that match the given predicate",
                SCALAR));
    }