D constructor problem

original text

/// module g.d
class world
{
    
atlasHandler atlas;

void do()
    {
    
    atlas = new AtlasHanlder();
    elf e = new elf(atlas);
    }
}

/// module 'objects.d'
class atlasHandler{
    }

class elf
{
    
this(atlasHandler atlas)
    {
    
    assert(atlas !is null); // normal 
    assert(g.world.atlas !is null); // collapse 

    writefln("atlas [%p] vs g.world.atlas [%s]", atlas, g.world.atlas);
    //  read g.world.atlas when , collapse .
    }
}

world by null Because it is not constructed success . There are Segment error .
It's also like you used to Segment error The source of the . you are here Constructors There is Circular reference . namely , You are constructing Global world instance , It is constructed again visit The constructor has not been completed The whole world Refer to the elf example , therefore Global world reference It's still empty .

If you're building The world , And you need to access it , Can be :
1, Use idle Destructor Incipient world , And then call... On it setup Methods do the work of the constructor ;
2, from The world Passed in constructor this Give it to all who need it Constructors .
similar :

import std.stdio : writeln;

class Foo {
    
    Bar b;
    this() {
     b = new Bar; }
    void sayMyName() {
     writeln(" ha-ha ."); }
}

class Bar {
    
    this() {
     f.sayMyName(); }
}

Foo f;

void main()
{
    
    f = new Foo;
}

Module independent . It is quote Oneself .
stay Constructors Return to the former , Construct instance quote by null. And in modular , Function field, etc It doesn't matter . If Not constructed success ( Segment error , Abnormal throwing , Conclude failure, etc ), be quote Always be null.
quote No example . It is an example The pointer . Already called Constructors when example It works , because this References must be valid . Consider ordinary function calls :

T newT() {
    
    T t = allocT();
    t.construct(t);
    return t;
}

T g = newT();

If t.construct Throw or collapse , It won't be implemented return t, Nor will it be incipient g.