The document could be more clear on when to and not to use `comptime`

[AndrewCodeDev]

I would check out this thread to get more context on this issue: How to force runtime evaluation?

I believe @kristoff’s answer is still up-to-date:

@kristoff

The rule right now is that a function is called at comptime implicitly only when you’re already in a comptime context, otherwise it will need to be prefixed with comptime. There has been discussion about eventually have the compiler “try” to resolve function calls at comptime without explicitly asking for it, but none of that exists today.

So a function call in the top scope of a file is always comptime, while a function call inside main is always at runtime unless prefixed with comptime.

Also, we need to make a distinction here between const and comptime. A good instance of this is in the typical declaration of strings [] const u8 which is a slice of constant unsigned 8-bit integers. The const there says nothing about comptime as it’s embedded in a non-const type.

Then there are certain positions where comptime must be implied. For instance, in the deduction of return types: Implementing Generic Concepts on Function Declarations - #13 by AndrewCodeDev