Create an array with immutable elements

[Roman D. Boiko]

On Friday, 15 June 2012 at 00:18:23 UTC, Jonathan M Davis wrote:
> On Friday, June 15, 2012 01:57:35 Roman D. Boiko wrote:
>> immutable struct Node{ string s; }
>> Node[] f()
>> {
>> Node[] arr = ...?
>> return arr;
>> }
>> 
>> How to fill an array, if its elements are immutable? I want to
>> assign values calculated by some function.
>
> There are 3 options that I know of:
>
> 1. Create an empty array and append the elements to it.
>
> 2. Use Appender (which will be more efficient than #1). e.g.
>
> auto app = appender!(immutable Node[])();
> app.put(value1);
> app.put(value2);
> //...
> auto arr = app.data;
>
> 3. Create the array as mutable and then cast it to immutable.
>
> auto arr = new Node[](length);
> arr[0] = value1;
> arr[1] = value2;
> //..
> auto immArr = cast(immutable(Node)[])arr;
>
> or better
>
> auto immArr = assumeUnique(arr);
>
> though that will make the whole array immutable rather than 
> just the Nodes -
> though that can be fixed by doing
>
> auto immArr = assumeUnique(arr)[];
>
> since array slices are tail-const.
>
> - Jonathan M Davis
Please note that type of Node is immutable. So the third option 
is disallowed. But I got enough answers, thanks to everybody!