Tjyylli

Let's say I want to call a method like:

doSomething(a.b.c.d.e.f());

I know that this might be an expensive operation and a, a.b, a.b.c, a.b.c.d, and a.b.c.d.e might all be null, however I would rather deal with all these possibilities within doSomething() is there any way I can defer that operation until I want/need it?

(I'm 99% certain the answer is 'no', but I hope to learn that I'm wrong.)

Not exactly, but you can do something like lazy evaluation by making use of the Callable interface (or rolling your own). Here's an example using Callable...

To start with, a test:

@IsTest private class LazyTest {



    @TestSetup static void setup() {

        List<Account> accounts = new List<Account> {

                new Account(Name = 'A'),

                new Account(Name = 'B')};



        insert accounts;



        List<Contact> contacts = new List<Contact> {

                new Contact(LastName = '1', AccountId = accounts[0].Id),

                new Contact(LastName = '2', AccountId = accounts[1].Id)};



        insert contacts;

    }



    @IsTest static void testBehavior() {

        Callable lazyContacts = new LazyContacts(new LazyAccounts('A'));

        // No calls made yet, so I can pass this around at no great cost

        System.assertEquals(0, Limits.getQueries());



        // OK, I've decided I need those contacts now...

        List<Contact> results = (List<Contact>)lazyContacts.call(null, null);

        System.assertEquals(2, Limits.getQueries());

        System.assertEquals(1, results.size());

        System.assertEquals('1', results[0].LastName);

    }

}

In the test, lazyContacts is not yet the Contacts I'm looking for. It's like a Callable that will provide the Contacts when I actually need them. It's parameterised by another Callable, so that inner one is also not invoked until you decide you actually need it.

The actual implementations:

public with sharing class LazyContacts implements Callable {



    private Callable lazyAccounts;



    public LazyContacts(Callable lazyAccounts) {

        this.lazyAccounts = lazyAccounts;

    }



    public Object call(String param1, Map<String, Object> param2) {

        return [

                SELECT LastName

                FROM Contact

                WHERE AccountId IN :(List<SObject>)lazyAccounts.call(null, null)

        ];

    }

}



public with sharing class LazyAccounts implements Callable {



    private String accountName;



    public LazyAccounts(String accountName) {

        this.accountName = accountName;

    }



    public Object call(String param1, Map<String, Object> param2) {

        return [

                SELECT Id

                FROM Account

                WHERE Name = :accountName

        ];

    }

}

You could certainly put together something like that in Apex. And you can do similar with iterators - only iterating when the data is actually requested.

The only downside is that Apex is missing a few language niceties that exist in Java and would make the code more succinct (and type-safe if we had templates).