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Hub AI
Union type AI simulator
(@Union type_simulator)
Hub AI
Union type AI simulator
(@Union type_simulator)
Union type
In computer science, a union is a value that may have any of multiple representations or formats within the same area of memory; that consists of a variable that may hold such a data structure. Some programming languages support a union type for such a data type. In other words, a union type specifies the permitted types that may be stored in its instances, e.g., float and int. In contrast with a record, which could be defined to contain both a float and an integer; a union would hold only one at a time.
A union can be pictured as a chunk of memory that is used to store variables of different data types. Once a new value is assigned to a field, the existing data is overwritten with the new data. The memory area storing the value has no intrinsic type (other than just bytes or words of memory), but the value can be treated as one of several abstract data types, having the type of the value that was last written to the memory area.
In type theory, a union has a sum type; this corresponds to disjoint union in mathematics.
Depending on the language and type, a union value may be used in some operations, such as assignment and comparison for equality, without knowing its specific type. Other operations may require that knowledge, either by some external information, or by the use of a tagged union.
Because of the limitations of their use, untagged unions are generally only provided in untyped languages or in a type-unsafe way (as in C). They have the advantage over simple tagged unions of not requiring space to store a data type tag.
The name "union" stems from the type's formal definition. If a type is considered as the set of all values that that type can take on, a union type is simply the mathematical union of its constituting types, since it can take on any value any of its fields can. Also, because a mathematical union discards duplicates, if more than one field of the union can take on a single common value, it is impossible to tell from the value alone which field was last written.
However, one useful programming function of unions is to map smaller data elements to larger ones for easier manipulation. A data structure consisting, for example, of 4 bytes and a 32-bit integer, can form a union with an unsigned 64-bit integer, and thus be more readily accessed for purposes of comparison etc.
ALGOL 68 has tagged unions, and uses a case clause to distinguish and extract the constituent type at runtime. A union containing another union is treated as the set of all its constituent possibilities, and if the context requires it a union is automatically coerced into the wider union. A union can explicitly contain no value, which can be distinguished at runtime. An example is:
Union type
In computer science, a union is a value that may have any of multiple representations or formats within the same area of memory; that consists of a variable that may hold such a data structure. Some programming languages support a union type for such a data type. In other words, a union type specifies the permitted types that may be stored in its instances, e.g., float and int. In contrast with a record, which could be defined to contain both a float and an integer; a union would hold only one at a time.
A union can be pictured as a chunk of memory that is used to store variables of different data types. Once a new value is assigned to a field, the existing data is overwritten with the new data. The memory area storing the value has no intrinsic type (other than just bytes or words of memory), but the value can be treated as one of several abstract data types, having the type of the value that was last written to the memory area.
In type theory, a union has a sum type; this corresponds to disjoint union in mathematics.
Depending on the language and type, a union value may be used in some operations, such as assignment and comparison for equality, without knowing its specific type. Other operations may require that knowledge, either by some external information, or by the use of a tagged union.
Because of the limitations of their use, untagged unions are generally only provided in untyped languages or in a type-unsafe way (as in C). They have the advantage over simple tagged unions of not requiring space to store a data type tag.
The name "union" stems from the type's formal definition. If a type is considered as the set of all values that that type can take on, a union type is simply the mathematical union of its constituting types, since it can take on any value any of its fields can. Also, because a mathematical union discards duplicates, if more than one field of the union can take on a single common value, it is impossible to tell from the value alone which field was last written.
However, one useful programming function of unions is to map smaller data elements to larger ones for easier manipulation. A data structure consisting, for example, of 4 bytes and a 32-bit integer, can form a union with an unsigned 64-bit integer, and thus be more readily accessed for purposes of comparison etc.
ALGOL 68 has tagged unions, and uses a case clause to distinguish and extract the constituent type at runtime. A union containing another union is treated as the set of all its constituent possibilities, and if the context requires it a union is automatically coerced into the wider union. A union can explicitly contain no value, which can be distinguished at runtime. An example is: