How to simplify nested ifs

[aliak]

On Tuesday, 13 March 2018 at 13:13:07 UTC, rumbu wrote:
> On Tuesday, 13 March 2018 at 12:23:06 UTC, Ozan Süel wrote:
>> Hi
>>
>> I have a construction like the following
>>
>> if (source) {
>>   if (source.pool) {
>>     if (source.pool.repository) {
>>       if (source.pool.repository.directory) {
>> 	if (source.pool.repository.directory.users) {
>> 	  // do something
>>
>> Any chance to simplify this nested ifs?
>> I know some languages has a way like.
>>
>> if (source?pool?repository?directory?users) // do something
>>
>>
>> Similar ways in D?
>>
>> Thanks and Regards, Ozan
>
> You need the null conditional operator which is not available 
> in D.
>
> A library solution can be found there: 
> https://forum.dlang.org/post/mailman.2562.1403196857.2907.digitalmars-d@puremagic.com
>
> SafeDeref(source).pool.repository.directory.users

This library may help as well: 
https://code.dlang.org/packages/optional

It will handle safe dispatching of reference types and pointer 
types and give you back the actual return result as well wrapped 
up in an optional value.

class C0 {
     C1 f() { return new C1(); }
     class C1 {
         C2 f() { return new C2(); }
         class C2 {
             int f() { return 0; }
         }
     }
}

auto res1 = some!C0(null).dispatch.f.f.f; // all no ops
auto res2 = some!C0(new C0()).dispatch.f.f.f // calls all fs

assert(res1 == none);
assert(res2 == some(0));