Re: Creating an array of immutable objects

[Ali Çehreli via Digitalmars-d-learn]

On 02/13/2017 04:59 PM, David Zhang wrote:

I have a struct with two immutable members, and I want to make an array
of them. How do I to this? I'm using allocators for this.

I realize that I misunderstood you; see below for a mutable array.

The following code produces an immutable array through the use of the 
misplaced std.exception.assumeUnique. (Why is it in std.exception? :) )

import std.stdio;
import std.algorithm;
import std.range;

string[] paths = [ "hello", "world" ];

struct FileDesc {
    immutable string path;
    immutable uint index;
}

immutable(FileDesc[]) _fileDesc;

FileDesc[] makeFileDescs(string[] paths) pure {
    return paths.enumerate!uint.map!(t => FileDesc(t[1], t[0])).array;
}

static this() {
    import std.exception : assumeUnique;
    auto fd = makeFileDescs(paths);
    _fileDesc = assumeUnique(fd);
}

void main() {
    _fileDesc.each!writeln;
}

A mutable array is simpler:

import std.stdio;
import std.algorithm;
import std.range;

string[] paths = [ "hello", "world" ];

struct FileDesc {
    immutable string path;
    immutable uint index;
}

FileDesc[] _fileDesc;

FileDesc[] makeFileDescs(string[] paths) pure {
    return paths.enumerate!uint.map!(t => FileDesc(t[1], t[0])).array;
}

static this() {
    _fileDesc = makeFileDescs(paths);
}

void main() {
    _fileDesc.each!writeln;
}

Ali