How do I use CTFE to generate an immutable associative array at compile time?

[Chad Joan via Digitalmars-d-learn]

Hello all,

I'm trying to make this work:

---
pure string[string] parseTwoColumnCsv(string inputCsv)
{
	import std.csv;
	import std.typecons;
	
	string[string] result;
	
	foreach ( record; csvReader!(Tuple!(string,string))(inputCsv) )
		result[record[0]] = record[1];
	
	return result;
}

immutable string[string] dataLookup = 
parseTwoColumnCsv(import("some_data.csv"));

void main()
{
	import std.stdio;
	writefln("dataLookup = %s", dataLookup);
}
---

But (with DMD 2.073.1) I am getting this error:
main.d(14): Error: non-constant expression [['a', 'b', 'c']:['x', 
'y', 'z'], ['1', '2', '3']:['4', '5', '6']]


The case with normal (non-associative) arrays seems to work fine, 
but is not what I needed:

---
pure string[][] parseTwoColumnCsv(string inputCsv)
{
	import std.csv;
	import std.typecons;
	
	string[][] result;
	
	foreach ( record; csvReader!(Tuple!(string,string))(inputCsv) )
		result ~= [record[0],record[1]];
	
	return result;
}

immutable string[][] dataLookup = 
parseTwoColumnCsv(import("some_data.csv"));

void main()
{
	import std.stdio;
	writefln("dataLookup = %s", dataLookup);
}
---

Any idea how I can get this working?

I have tried a couple other things, like having the 
parseTwoColumnCsv function return an immutable string[string] and 
casting 'result' to that in the return statement, and I also 
tried just casting the value returned from parseTwoColumnCsv as 
it appears in the declaration of 'dataLookup'.  I tried 
std.exception's assumeUnique, but the function/template signature 
doesn't seem to support associative arrays.

Thanks.