Tricky operator = overload

[sebbarg]

Nitpick: violation of Principle of Least Surprise in operator overload = ?

Given an empty cache, this throws an exception ("A value is not available for this instance") on line 2:

var value = await cache.TryGetAsync<PocoA?>(key);
var poco = (PocoA?)value; // => throws exception

I would expect it to assign null to poco.

This works as expected, so I guess that is the way to go?

var value = await cache.TryGetAsync<PocoA?>(key);
var poco = value.GetValueOrDefault(); // => poco == null

[jodydonetti]

Hi @sebbarg

Nitpick: violation of Principle of Least Surprise in operator overload = ?

Given an empty cache, this throws an exception ("A value is not available for this instance") on line 2:

var value = await cache.TryGetAsync<PocoA?>(key);
var poco = (PocoA?)value; // => throws exception

I would expect it to assign null to poco.

Not really: by saying PocoA? you are expressing that the value can be "either PocoA or null".
Then you call TryGet which returns a MaybeValue<PocoA?>, allowing you to know if:

• the value IS NOT in the cache (HasValue = false)
• the value IS in the cache (HasValue = true) and in that case if value is:
  • null
  • a non-null value

So by forcing a MaybeValue<PocoA?> with HasValue = false into a PocoA? it is correctly throwing an exception.

Otherwise you would not be able to differentiate between "I'm receiving null because null is in the cache" and "I'm receiving null because there is nothing in the cache".

You are thinking about null as "the value is not in the cache", whereas null can in fact be in the cache, and is usually the right thing to do, to avoid having an easy to use DDoS venue.

This works as expected, so I guess that is the way to go?

var value = await cache.TryGetAsync<PocoA?>(key);
var poco = value.GetValueOrDefault(); // => poco == null

Yes exactly, because here you are saying "give me the value or, if not there, the default value of the type".

But I'll add that if you don't care to know IF the value is in the cache or not, you can just call GetOrDefault instead of TryGet, which I think it's even clearer.

Hope this helps, let me know.

[sebbarg]

Ah... of course the key can point to a null-value. Sorry. That get's me every time 🙈

Thanks for GetOrDefault hint, that makes perfect sense!