The Fortress Language Specification - CiteSeerX

This method runs all test functions defined in the component. All test functions are run in parallel; each test function
is run for each combination of test cases (bound in its generator list as described in Section 19.2) in parallel. In the
case of a compound component, the set of defined test functions consists of all test functions defined by all constituent
components and by all exported APIs. The set of test functions run can be limited by first hiding the tested component
in a more restrictive API. The set of test functions can also be expanded by linking with a component defining
additional test functions.
The runTests method includes a keyword parameter inclusive that defaults to true . If this parameter is set to false ,
only test functions defined in the APIs exported by the component are run.
22.8 Advanced Features of Fortress Operations
The system we have described thus far provides much of the desired functionality of a component system. However it
has a few significant weaknesses:
1. It exposes to everyone all the APIs used in the development of a project.
2. By allowing access to these APIs, it inhibits significant cross-component optimization.
3. It prevents components that use two different implementations of the same API from being linked, even if they
never actually pass references to that API between each other.
4. It restricts the upgradability of compound components, as described earlier.
We can mitigate all these shortcomings by providing two simple operations, hide and constrain. Informally, hide
makes APIs no longer visible from outside the component so that they cannot be upgraded, and constrain merely
prevents them from being exported. An API that is constrained but not hidden can still be upgraded. There are other
subtle consequences of this distinction, which we discuss as they arise.
Some of the properties about the APIs exported by a component discussed in Section 22.7 are actually properties of
APIs that are visible or provided by a component. For example, APIs visible in a component cannot be imported by
that component, even if they are not exported. Other properties are really properties only of the exported APIs. Most
importantly, components that do not export any common APIs can be linked, as can components that share only visible
APIs.
Constrain A constrain operation takes a component name of an installed component, a new component name,
and a set of APIs, and produces a new component that does not export any of the APIs specified. Syntactically, we
write:
constrain(source:String, destination = source, apis:Set[\String\]):()
If no destination name is provided, the name of the source is used.
The set of APIs provided must be a subset of the APIs exported by the component. Also, recall that every API used
by an API exported by a component must be imported or exported by that component. Thus, if we constrain an API
that is used by any other API exported by the component, then we must also constrain that other API.
If the component is a simple component, we first link it by itself, and then apply constrain to the result.
Hide A hide operation is like a constrain operation, except that the given set of APIs is subtracted from the
visible and provided APIs, along with the exported APIs, in the resulting component.
hide(source:String, destination = source, apis:Set[\String\]):()
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