‘disposable’ Variables

A lot of classes in Jancy standard library (e.g. io.File, io.Serial, etc.) provide close methods to terminate the current session and release associated resources.

If an instance of such class is being abandoned without having its close method called, it will still be called automatically in the class destructor – which will happen whenever the Jancy Garbage Collector decides to sweep unused objects.

However, leaving this at Garbage Collector’ discretion is undesirable, as it leads to undeterministic resource release – file handle or other resources will be held for an unknown period of time.

An easy way for overcoming this problem is to work with objects that do require a timely invokation of close (or similar resource-releasing method) using the Jancy disposable storage specifier.

Example:

void foo() {
    // ...

    disposable io.File file;
    file.open();

    // work with file...
} // <-- file.close() is guaranteed to be called upon exiting the scope

When program runs out of scope where a variable of disposable class was declared in, Jancy compiler will insert a call to dispose method (which is usually aliased to an actual release methods such as close). This method will be called no matter how the program runs out of scope, be it a normal control flow, return, break, continue or an exception.

You can easily write disposable classes yourself. All you have to do is to provide a dispose method:

class MyDisposableClass {
    void dispose() {
        printf("Releasing resources...");
    }
}

void foo() {
    // ...

    disposable MyDisposableClass c;

    // work with c...

    throw; // <-- c.dispose() will get called
}

Often times, a class already has a function to release resources (called close, release, etc.); renaming it to dispose may be undesireable. In such case, you cane make such a class disposable by aliasing dispose:

class MyDisposableClass {
    void close(); // a natural name for a resource-releasing method
    alias dispose = close;
}