Checking if CTFE is used?

[MachineCode]

On Tuesday, 18 December 2018 at 14:23:38 UTC, berni wrote:
> On Tuesday, 18 December 2018 at 13:53:01 UTC, Stefan Koch wrote:
>> Why would you need to know?
>
> Well, first out of curiosity. But there are also other reasons: 
> I've got a large immutable array. Without CTFE I'd use some php 
> script and add it as a large literal. With CTFE I don't need 
> that php script nor do I need to put that large literal in the 
> source code. But I need to know, that indeed the array is 
> calculated by the compiler, else the solution with the php 
> script would result in faster code.
>

How is the items in the array generated? if the function can be 
called as following:

> enum myArr = generateArray();

then you know for sure you have a satic array of strings at 
compile time.
I've used something similar, to generate a JSON string from all 
UDAs in a give class, which I needed to pass to a C# application 
(I made the D output a string from the request by command line 
option). I did something like this:

string getAvailableForms()
{
	import extensions.enumeration : staticMembers;
	import asdf; // JSON serializer
	import std.traits : getUDAs, hasUDA;
	import externalPaths : ExternalAppPath, DisplayName;
	import std.algorithm : startsWith;
	import std.conv : to;

	FormDisplayNameObj[] output;
	static foreach(string fieldName; staticMembers!ExternalAppPath)
	{{
		static if(hasUDA!(__traits(getMember, ExternalAppPath, 
fieldName), DisplayName))
		{
			if(fieldName.startsWith(startKey))
			{
				DisplayName dn = getUDAs!(__traits(getMember, 
ExternalAppPath, fieldName), DisplayName)[0];
				string id = extractDigits(fieldName[startKey.length - 1 .. 
$]);
				int i  = to!int(id);
				auto o = new FormDisplayNameObj();
				o.value = dn.value;
				o.index = i;
				output ~= o;
			}
		}
	}}
	return output.serializeToJson;
}

then:

enum s = getAvailableForms;
writeln(s);

I did consider at first make a script to generate that string but 
I managed to make it work with CTFE that way.