distributed computing A distributed system is a system whose components are located on different networked computers, which communicate and coordinate their actions by passing messages to one another from any system. Distributed computing is a field of computer sci ...

, a discriminator is a typed tag field present in OMG IDL discriminated union type and value definitions that determines which union member is selected in the current union instance. Unlike in some conventional programming languages offering support for unions, discriminator in IDL is not identical to selected field name. Here is an example of IDL union type definition: union Register switch (char) ; Effective value of the ''Register'' type may contain AX as selected field, but discriminator value may be either 'a' or 'b' and it is stored in memory separately. Therefore, IDL logically separates information about currently selected field name and union effective value from information about current discriminator value. In the example above, discriminator value may be anything of the following: 'a', 'b', 'c', as well as all other characters belonging to the IDL char type, since the default branch specified in the example ''Register'' type allows use of the remaining characters as well.

Other languages

The Microsoft Interface Definition Language also supports tagged unions, allowing to choose the discriminator via an

attribute Attribute may refer to: * Attribute (philosophy), an extrinsic property of an object * Attribute (research), a characteristic of an object * Grammatical modifier, in natural languages * Attribute (computing), a specification that defines a prope ...

in an enclosing structure or function.Microsoft discriminator attribute documentation
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References

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