CTFE Returns

Remember that CTFE makes the compiler execute some code itself. We can specify that certain statements are to be evaluated by the compiler by adding the static keyword before other keywords such as if, foreach and assert.

Logger

We can optimise the foreach loop we’ve just written at compile time and have the compiler handle the iteration.

Concretely, we will change the foreach loop to a static foreach loop. This will make the compiler replace the loop with each separate step:

// This code:
static foreach (i; [1, 2, 3])
{
    writeln(i);
}

// is equivalent to:
writeln(1);
writeln(2);
writeln(3);

If you run into an error saying that declaration <some_variable> is already defined, keep in mind that unlike foreach, static foreach does not create a new scope. Read the 4th point from here to fix this error.

At this point, with a pretty short code base, our logger is capable of logging nearly any type:

• basic types
• arrays
• structures and classes

Now imagine doing this in any other object-oriented language you know: C++, Java, Python etc. Yes, D is that cool.