Why can't the compiler properly detect the type of Array!string("something")?

[Adnan]

On Saturday, 14 March 2020 at 23:39:11 UTC, Adnan wrote:
> In the following code the compiler says the type is 
> Array!()(string):
>
> 			if (key in wordTable)
> 				wordTable[key] ~= word;
> 			else
> 				wordTable[key] = Array!string(word);
>
>
> source/app.d(29,36): Error: template 
> std.container.array.Array!string.Array.__ctor cannot deduce 
> functi
> on from argument types !()(string), candidates are:
> /snap/dmd/99/bin/../import/phobos/std/container/array.d(467,5):
>      __ctor(U)(U[] values...)
>   with U = immutable(char)
>   must satisfy the following constraint:
>        isImplicitlyConvertible!(U, T)
> /snap/dmd/99/bin/../import/phobos/std/container/array.d(501,5):
>      __ctor(Range)(Range r)
>   with Range = string
>   must satisfy the following constraint:
>        isImplicitlyConvertible!(ElementType!Range, T)

Full code
string smallestRepr(const string arg) {
	auto repeated = arg ~ arg;
	string result = arg;
	foreach (i; 1 .. arg.length) {
		const slice = repeated[i .. i + arg.length];
		if (slice < result)
			result = slice;
	}
	return result;
}

unittest {
	assert("cba".smallestRepr() == "acb");
}

void main(const string[] args) {
	import std.stdio : write, File;
	import std.container : Array;

	Array!string[string] wordTable;

	foreach (string word; File(args[1]).byLineCopy()) {
		word = word[0 .. $ - 1]; // strip the newline character
		const string key = word.smallestRepr();
		debug {
			if (key in wordTable)
				wordTable[key] ~= word;
			else
				wordTable[key] = Array!string(word);
		}
		else {
			wordTable.require(key, Array!string()) ~= word;
		}
	}

	foreach (array; wordTable.values) {
		if (array.length == 4) {
			foreach (word; array) {
				write(word, ", ");
			}
			write("\n");
			break;
		}
	}
}