Digression: the comptime keyword

You probably know of comptime in Zig. Here we have an application of the concept: since the builtin.is_test variable is evaluated at compile time, the whole branch in getWindowSize() can be resolved at compile time, the relative code will be removed and will not be executed at runtime.

This has the same effect of an #ifdef block in C for conditional compilation, but the syntax looks much less intrusive. You can even force any expression to be evaluated at compile time by using the comptime keyword before the expression, but here it's not needed, because the builtin.is_test variable is guaranteed to be compile-time known.

While using the comptime keyword, sometimes the compiler complains that using the keyword is redundant, because the expression is always compile-time known, other times it doesn't complain, as in the case above, even if I'm pretty sure that all builtin variables are compile-time known. We saw another example in the main() function, where the allocator was chosen by testing the builtin.mode variable.

To my understanding, also from reading several posts made by the original creator of Zig (Andrew Kelley), most of the time it's not necessary to use the keyword, the compiler is smart enough to evaluate at compile time what it can, even if you don't specify it expressly. But sometimes the compiler says:

error: unable to resolve comptime value

In these cases the comptime keyword might fix the issue.

Bottom line: don't be compulsive in filling your code with comptime, it's not necessary.