Determining whether a module is available

We might want to compile some extension features if and only if another module is available at compile-time to gracefully degrade when a dependency isn't installed. The most straightforward solution is to use the version statement, passing the appropriate identifier to the dmd command line. Can we also do it without extra compiler options from the user?

How to do it…

Let's execute the following steps to determine whether a module is available:

1. Try to compile an anonymous function that does nothing other than import a module.

2. Use it conditionally by wrapping any use of the module inside the static if statement.

3. Instruct the user to enable the module by placing it at a location where the compiler can find it automatically, or by adding the following module to the compile command line.

The code is as follows:

static if(__traits(compiles, { import test.foo; })) {
    import test.foo; /* safe to use */
} else {
   // module not available, work around
}

How it...