Tuple enumeration without integers or strings

[Mike Parker]

On Sunday, 3 January 2021 at 13:36:57 UTC, Paul wrote:

> Is there an easy way for me to know when code is assessed / 
> generated at compile time?
> For example, is indexing a constant compile time array compile 
> time or run time?
> Or how about functions? The hashOf documentation does not seem 
> to hint to being done at compile time.

It's not what you do, but the context in which you do it. If a 
function must be evaluated at compile time, it will be.

```
string tellme() {
     if(__ctfe) return "Compile Time";
     else return "Run time";
}

void main()
{
     writeln(tellme());
     pragma(msg, tellme());
     writeln(tellme());
}
```

Since the msg pragma is a compile-time construct, tellme *must* 
be evaluated at compile time. The calls to writeln are just 
normal function calls, therefore the calls to tellme happen at 
runtime.

So any context where you replace a compile-time constant with a 
function call, you'll have CTFE (as long as it's possible [1]). 
It's common to use enum to force CTFE:

enum s = tellme();

[1] https://dlang.org/spec/function.html#interpretation