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Each Ice object has an object identity defined as follows:
As you can see, an object identity consists of a pair of strings, a
name and a
category. The complete object identity is the combination of
category, that is, for two identities to be equal, both
category must be the same. The
category member is usually the empty string, unless you are using servant locators or default servants.
Glacier2 also uses the
category member for filtering.
name is an empty string,
category must be the empty string as well. (An identity with an empty
name and a non-empty
category is illegal.) If a proxy contains an identity in which
name is empty, Ice interprets that proxy as a null proxy.
Object identities can be represented as strings; the category part appears first and is followed by the name; the two components are separated by a
/ character, for example:
In this example,
Factory is the category, and
File is the name. If the
category member themselves contain a
/ character, the stringified representation escapes the
/ character with a
\, for example:
In this example, the category is
Factories/Factory and the name is
Syntax for Stringified Identities
You rarely need to write identities as strings because, typically, your code will be using the identity helper functions
stringToIdentity, or simply deal with proxies instead of identities. However, on occasion, you will need to use stringified identities in configuration files. If the identities happen to contain meta-characters (such as a slash or backslash), or characters outside the printable ASCII range, these characters must be escaped in the stringified representation. Here are rules that the Ice run time applies when parsing a stringified identity:
- The parser scans the stringified identity for an un?escaped slash character (
/). If such a slash character can be found, the substrings to the left and right of the slash are parsed as the
namemembers of the identity, respectively; if no such slash character can be found, the entire string is parsed as the
namemember of the identity, and the
categorymember is the empty string.
- Each of the
category(if present) and
namesubstrings is parsed according to the following rules:
- All characters in the string must be in the ASCII range 32 (space) to 126 (~); characters outside this range cause the parse to fail.
- Any character that is not part of an escape sequence is treated as that character.
- The parser recognizes the following escape sequences and replaces them with their equivalent character:
- An escape sequence of the form
ois a digit in the range 0 to 7) is replaced with the ASCII character with the corresponding octal value. Parsing for octal digits allows for at most three consecutive digits, so the string
\0763is interpreted as the character with octal value 76 (
>) followed by the character
3. Parsing for octal digits terminates as soon as it encounters a character that is not in the range 0 to 7, so
\7xis the character with octal value 7 (bell) followed by the character
x. Octal escape sequences must be in the range 0 to 255 (octal 000 to 377); escape sequences outside this range cause a parsing error. For example,
\539is an illegal escape sequence.
- If a character follows a backslash, but is not part of a recognized escape sequence, the backslash is ignored, so
\xis the character
Identity Helper Functions
To make conversion of identities to and from strings easier, the
Communicator interface provides appropriate conversion functions:
For C++, Ruby, and PHP, the operations on the communicator are the only way to convert between identities and strings. For other languages, the conversion functions are provided as operations on the communicator as well but, in addition, the language mappings provide static utility functions. (The utility functions have the advantage that you can call them without holding a reference to the communicator.)
For C++, the static utility functions are not provided due to the need to apply string conversions, and the string converters are registered on the communicator.
For Java, the utility functions are in the
Ice.Util class and are defined as:
For C#, the utility functions are in the
Ice.Util class and are defined as:
The Python functions are in the
These functions correctly encode and decode characters that might otherwise cause problems (such as control characters).
As mentioned in Servant Activation and Deactivation, each entry in the ASM for an object adapter must be unique: you cannot add two servants with the same identity to the ASM.