Named Entities

This page provides more detail on the central named entities that are provided by Storm, and how they are used. As with most entities in the name tree, these entities can be extended by other languages to provide additional functionality. Other languages may, however, not be able to understand the additional information. As a concrete example, Basic Storm is not able to understand the syntax from the Syntax Language, since the Syntax Language adds such information in a subclass to the Type entity that Basic Storm is not aware of.

The name tree is built from named entities. The name tree is a linked structure with pointers both from the root to its leaves, but also from the leaves towards the root. The former does not always exactly match the latter. For example, it is typically desirable to be able to perform type lookups inside blocks in functions. As such, the blocks have a pointer to its parent in the tree to allow traversing it towards the root to inspect the static context. However, it is typically not interesting for individual blocks inside a function to be reachable from the root (they are anonymous). As such, languages typically only adds a pointer to entire functions to the name tree, but functions themselves do not contain pointers to all the contained blocks.

NameLookup

A core.lang.NameLookup represents something that can act as a starting point for name resolution. The NameLookup is itself not a named entity as it has no name. It is, however, one of the base classes for named entities in the system.

To accommodate name lookups, the NameLookup contains the following two members:

Users of NameLookup are encouraged to use the parent() function instead of the parentLookup variable directly. The default behavior of the parent() function is to assert whenever parentLookup is not set, as this typically indicates that a named entity was not properly added to the name tree. Implementations may, however, override parent to return null to indicate that the root of the name tree has been reached (e.g. for the root package).

As mentioned above it is, however, possible to set parentLookup manually to create entities that are not reachable from the root of the name tree (and thus not reachable by most parts of the system), but that may participate in name resolution. Typical examples of this is blocks inside of functions in a programming language. These are anonymous, so there is no value in making them accessible from the name tree. They do, however, contain variables, so it is useful to utilize the name resolution system already in Storm to lookup local and non-local variables.

In addition, the NameLookup class contains a number of convenience overloads for find.

LookupPos

The type core.lang.LookupPos is an intermediate class between NameLookup and Named. It adds a source position to indicate the current location. This is mainly used to implement file-private visibility. To determine if an entity is accessed from the same file, the visibilty check examines if a LookupPos is in the chain of parent pointers in order to determine the current source file.

Named

The core.lang.Named is the base for all named entities in the system. It inherits from LookupPos, and thereby indirectly from NameLookup. This means that it inherits a pointer to a parent entity in the name tree.

Apart from the parent entity, the Named type also contains a name. The name consists of two parts, a string and a list of zero or more parameters. It is stored as two members as follows:

The named entity also contains the member flags that indicate if the named entity should be treated specially during name lookup. Currently, the only flag that is available is NamedFlags:namedMatchNoInheritance, which specifies that inheritance should not be considered when matching parameters. This is typically desirable for templated types.

Apart from the name and flags, a named entity may also have a visibility. The visibility is represented as an instance of a subclass of core.lang.Visibility that is stored in the visibility member. If the visibility member is null, then the entity is considered to be visible from anywhere in the system. The utility function visibleFrom checks visibility using the visibility member.

Finally, the named entity may have an attached documentation entity in the documentation member. The function findDoc can be used to retrieve the documentation conveniently.

The following convenience functions are also available:

Function

The core.lang.Function entity is a named entity that represents a function. The parameters of the function entity are assumed to directly correspond to the formal parameters accepted by the function, including any implicit this parameters. The function also has a set of flags, marking it as pure, autocast, final, override, or static. The pure flag means that the system may assume that the function does not inspect nor modify any state outside of its parameters. Calls to pure functions may thereby be optimized away if desired.

Note that functions that correspond to constructors (named __init) are typically not possible to call directly.

A function contains one instance of the core.lang.Code class that contains the actualy code that should be executed by the function. Apart from that, the function contains two RefSources that other parts of the system may refer to. One RefSource always refers directly to the Code in the function, while the other may be modified to instead refer to any logic required for dynamic dispatch. Having two separate RefSources means that call-sites can specify if the dispatch logic should be called or not.

A function contains the following members:

The Function class also contain a number of functions to automatically generate code for calling the function. These are a number of variants, each with a number of overloads:

Code

The type core.lang.Code is the base class to a hierarchy of types for different situations. The ones most relevant when generating code from Storm are the followin ones:

Variable

The core.lang.Variable is a generic representation of a variable. It only has one additional member, namely: type that stores the type of the variable.

GlobalVar

The core.lang.GlobalVar entity inherits from core.lang.Variable and represents a global variable. Global variables are expected to only be accessible from a particular named thread to ensure thread safety. The global variable is lazily initialized by providing a function pointer that contains the initialization logic.

MemberVar

A core.lang.MemberVar entity is a variable that is a member of a type. As such, it does not provide any storage for the actual variable itself, but cooperates with the Type entity to allocate storage in the type.

NamedThread

The core.lang.NamedThread entity represents a named thread in the system. The NamedThread entity is essentially a thin wrapper around a Thread object, that also contains a name and allows accessing it easily in generated code through a reference.

NameSet

The core.lang.NameSet entity is a named entity that may contain zero or more other named entities. It is thus the type responsible for the central nature of the name tree. As the name implies, all entities stored inside of it need to have unique names.

The NameSet provides the following members for inspecting and manipulating its content:

Apart from storing entities, the NameSet provides two mechanisms for dynamically generating named entities on demand. The first one is through a mechanism called templates. A template in Storm is essentially just a callback with a name without parameters. When a template is inserted into a NameSet, then the NameSet will execute the callbacks in all templates associated with the name that is beeing looked up whenever it does not already contain a suitable named entity. The templates are thus free to inspect the parameters and determine if they wish to generate a suitable named entity on demand or not. If they do, the named entity is inserted into the name set and used for future lookups.

The functions used to manipulate templates are as follows:

The second mechanism is lazy-loading. This mechanism relies on overloading protected members, and therefore it requires subclassing the NameSet entity. A name set is initially in the unloaded state. This means that whenever it fails to find a named entity (after template lookup), it will attempt to load its content. This occurs in two steps. In the first step, the NameSet calls the function loadName to attempt to load only the requested name. If it is successful, the name set concludes its search and remains in the unleaded state. If loading of a single entity fails (e.g. because it is not supported), then the loadAll function is called instead. This instructs the derived class to load all entities into the NameSet. After this, the NameSet switches to the loaded state, which means that it will no longer attempt lazy loading.

In most cases, lazy loading is transparent to the user of the interface, as the NameSet will handle loading transparently. The exception is, however, iterating through the NameSet. Doing this will not cause automatic loading, as that would make it impossible to traverse the currently loaded parts of the name tree. Instead, the forceLoad member is available to force the NameSet to load all its content early.

The following members are used for lazy loading:

The default implementation of the loadName and loadAll functions above simply return false and true respectively. This means that lazy-loading will succeed, but not load anything if they are not overridden. This means that it is possible to ignore lazy-loading unless it is needed.

Package

The core.lang.Package extends core.lang.NameSet and represents a package in the system. Packages generally correspond to directories in the file system, but it is also possible to create virtual packages that do not exist on disk. Virtual packages must therefore be populated manually.

The package entity add two main things to the interface of NameSet: automatic discarding of source code and exports. By default, a package will automatically ask all loaded entities to discard references to source code after they are loaded. This means that it is not possible to ask functions to re-generate intermediate code once they are created, for example. This is usually desired, as it is only necessary to generate code for each function exactly once. In some cases, however, it is desirable to inspect and modify the generated code. In such cases, the automatic discarding needs to be disabled by calling retainSource.

The other concept, exports, allows a package to specify that other packages should be included alongside it. For example, if a language extension in package a adds to the syntax in b, then a will not work unless b is also included. To avoid confusion, a can express this dependency by exporting b. This means that including a from a language implicitly also includes b.

The additional interface consists of the following members:

Type

The entity core.lang.Type also extends core.lang.NameSet. It represents a type in the type system. As such, it extends the interface of NameSet with functionality for managing inheritance, object layout, for example. The MemberVar entity (see above) is specially recognized by the Type entity. They collaborate to provide object layout.

What kind of type is represented is set on construction through the TypeFlags parameter. It can also be retrieved using the typeFlags member. The Value class can also be used to inspect types conveniently.

As with many other parts of Storm, the Type class generates its contents lazily. This means that it is possible to modify the contents of a type until the first instance is created. At that point, the object layout is finalized, and members may no longer be added or removed. This restriction does, however, not apply to functions that do not rely on virtual dispatch, or other named entities.

The Type entity provides the following additional member functions: