XCSG:Variable
The term variable is used by many authors to refer to any assignable entity. Unfortunately the same term is used by others to refer only to local variables. In XCIL, we use the terms Variable (for any assignable entity) and LocalVariable (for a variable defined by a method body).
The semantics of Variable are those common to all its subtypes, i.e. Attribute, AssociationEnd, ArrayElement, Parameter, and LocalVariable.
The meaning of volatile is that common to C++ and Java.
Specifications
| Metaclass | Variable |
|---|---|
| Extends | AddressableEntity |
| Description | An assignable entity that represents a portion of the system’s state, i.e. an attribute, an array element, an out or inout parameter, or a local variable. |
| Direct Subkinds | CallInput, Field, ProgramVariable, StackVariable |
|---|
| All Superkinds | Node, ModelElement |
|---|
| Specified In Edges | |||
|---|---|---|---|
| In Edge | Predecessor | Multiplicity | Description |
| DataFlow (Edge) | DataFlow (Node) | ✱ | Connects DataFlow nodes to one another and to Variables, linking the origin of data to locations that it is modified or consumed. |
| Specified Out Edges | |||
|---|---|---|---|
| Out Edge | Successor | Multiplicity | Description |
| DataFlow (Edge) | DataFlow (Node) | ✱ | Connects DataFlow nodes to one another and to Variables, linking the origin of data to locations that it is modified or consumed. |
| DefinedAs | TypeAlias | 0..1 | Connects a Variable or DataFlow node which received its Type via a TypeAlias (such as a C/C++ typedef) to that TypeAlias. |
| InstanceVariableWritten | InstanceVariableAssignment | ✱ | Connects a value (DataFlow (Node) or Variable) representing an object instance to an InstanceVariableAssignment representing a write to a field of that object. |
| TypeOf | Type | 1 | Links a Variable or DataFlow node to its Type |
| Known Possible In Edges | ||||
|---|---|---|---|---|
| In Edge | Predecessor | Multiplicity | Description | |
| HasVariable | Namespace | 1 | Links a Classifier or Package to one of its Variables. | |
| InterproceduralDataFlow | Assignment | ✱ | Represents data flows between Functions, or involving Variables visible to multiple Functions.
| |
| Inherited From | In Edge | Predecessor | Multiplicity | Description |
| Node | Contains | Node | 1 | Indicates that the predecessor contains the successor in a sense specified by the specific type of Contains edge. |
| Known Possible Out Edges | ||||
|---|---|---|---|---|
| Out Edge | Successor | Multiplicity | Description | |
| InterproceduralDataFlow | DataFlow (Node) | ✱ | Represents data flows between Functions, or involving Variables visible to multiple Functions.
| |
| Inherited From | Out Edge | Successor | Multiplicity | Description |
| Node | Contains | Node | ✱ | Indicates that the predecessor contains the successor in a sense specified by the specific type of Contains edge. |
| Tag | volatile |
|---|---|
| Description | Present if the code indicates the variable requires special treatment because the variable's value can be changed externally, e.g. by hardware. |
| Tag | memoryBarrier |
|---|---|
| Description | Indicates that reading from the variable creates a "happens before" relationship to any code (in any thread) that previously wrote to the variable. |
| Tag | immutable |
|---|---|
| Description | Present if the variable cannot be changed after initialization. |
Language mappings
The volatile tag maps exactly to the volatile keyword in C and C++. Note that other languages, notably C# and Java (since 1.5), use the same keyword, but additionally require a memory barrier or "happens after" relationship; for such variables, both the volatile and memoryBarrier tags should be present.
Individual language mappings are provided for each subtype of Variable (Attribute, AssociationEnd, ArrayElement, Parameter, and LocalVariable).
