CORBA Any’s and TypeCodes

Martin Senger

senger@ebi.ac.uk

We want something, but we do not know what...

• Type-safety vs. flexibility– type-safe are objects with type known at the

compile time - but it limits developers– most often the type-safe problems end by

crashing programs - but not breaking security– inheritance is (probably) also sort of type-

unsafe

• Methods to find the “real” type:– type-casting, narrowing, testing a variable,...

In CORBA, there are:

• org.omg.CORBA.Object– a super-class to all CORBA Objects– represents (only) interfaces– narrowing to the “real” type can be costly

• Any– and we are going to talk about it in details...

• DynAny– that’s a new story… - an extension of Any’s

A place of Any’s in CORBA

EntityEntity

Object referenceObject reference

Value TypeValue Type

Abstract InterfaceAbstract Interface

Basic ValueBasic Value

Constructed ValuesConstructed Values

StructSequenceUnionArray

StructSequenceUnionArray

ShortLongLongLongUShortULongULongLongFloatDoubleLongDoubleFixedCharWCharStringWStringBooleanOctetEnumAny

ShortLongLongLongUShortULongULongLongFloatDoubleLongDoubleFixedCharWCharStringWStringBooleanOctetEnumAny

Some features...

• The any type permits the specification of values that can express any OMG IDL type

• An any contains a TypeCode and a value that is described by the TypeCode

• Each IDL language mapping provides operations that allow to insert and access the TypeCode and value contained in an any

Remember: The golden rule

• You can pass in Any only “things” whose types are known to the receiving program already in time of compilation

• Therefore the “things” in Any can be only– basic IDL types (boolean, float,…)– sequences of (most) basic IDL types

• String and WString are exceptions

– types defined in IDL files known to both sites of communication

Creating Any’s (in Java)

• create an empty Any:Any any = orb.create_any();

• insert the value into the Any– for basic IDL types:

String str = “Hello World”;any.insert_string (str);

– for compiled IDL types use their Helper classes:MyClass myClass = new MyClass (…);MyClassHelper.insert (any, myClass);

– for sequences of basic IDL types use their Helper classes that are provided by ORB:

int[] myNumbers = new int[] { 1, 2, 3, 4, 6 };ShortSeqHelper.insert (any, myNumbers);

Extracting from Any’s (in Java)

• extract the value from an Any– for basic IDL types:

int number = any.extract_short();

– for compiled IDL types use their Helper classes:MyClass myClass = MyClassHelper.extract (any);

– for sequences of basic IDL types use their Helper classes that are provided by ORB:

int[] myNumbers = ShortSeqHelper.extract (any);

• of course, first you have to know what type you have got in the Any...

CORBA TypeCodes

• TypeCodes are values that represent data types

• TypeCode is described as a CORBA interface– with methods to enquire what type it represents,– to ask if two TypeCodes are equal or equivalent,– and with some exceptions (BadParam, Bounds)

• TypeCodes are used in Any’s, by Interface Repository, by DII, etc...

The contents of a TypeCode• a “kind” field

enum TCKind {tk_null, tk_void,tk_short, tk_long, tk_ushort, tk_ulong,tk_float, tk_double, tk_boolean, tk_char,tk_octet, tk_any, tk_TypeCode, tk_Principal, tk_objref,tk_struct, tk_union, tk_enum, tk_string,tk_sequence, tk_array, tk_alias, tk_except,tk_longlong, tk_ulonglong, tk_longdouble,tk_wchar, tk_wstring, tk_fixed,tk_value, tk_value_box,tk_native,tk_abstract_interface

};

• a set of parameters appropriate for that “kind”

TypeCode parameters

TCKind Parameters tk_fixed Digits, scale tk_objref Repository ID, interface name tk_struct Structure name,

{ member name, member type code }… tk_union Union name, discriminator type code,

{ label value, member name, member type code }…, repository ID

tk_enum Enum name, { enumerator name }…, repository ID tk_string Bound tk_wstring Bound tk_sequence Element type code, bound tk_array Element type code, dimension tk_alias Alias name, aliased type code, repository ID tk_except Exception name, { member name, member type code }

repository ID

From the book: “Advanced CORBA Programming with C++” by Michi Henning and Steve Vinoski

Each TypeCodehas a “kind”

field...

…and for each“kind” field ithas differentparameters

Some TypeCode’s special kinds

• tk_null– this TC does not describe anything (“not-there” condition)

• tk_TypeCode– to insert TypeCodes into an Any

• tk_alias– describes typedef definitions

• tk_any– because an Any can contain another Any

• tk_void– used in the Interface Repository (never in Any’s)

Where TypeCodes come from

• don’t bother, usually they are created for you

• Helper classes have method returning TC:TypeCode tc = MyClassHelper.type();

• ORB has methods for creating TC’s (examples):TypeCode create_struct_tc (

in RepositoryId id,in Identifier name,in StructMemberSeq members);

TypeCode get_primitive_tc (in TCKind tcKind);

Notes on hands-on• [skipping Any’s => will be done in Property

Service hands-on]

• TypeCodes– go to directory “TypeCodes”– compile “ExerciseTypeCodes.idl”– implement conversion methods “stringToEnum”,

“enumToString”, and “printAll” in the example “ReadingColors.java”

– hint: look what parameters are available for “kind” enum