C#•2y ago

❔ How to make a method returning type T but only taking subclasses of a certain class ?

I'd like to make a function that takes the type T as an "argument" (T MyMethod<T>()), but the type T must be equal to Type Z or subclass of Type Z, how do I do that ? I'd like it search through defined dictionaries that are all typed as subclasses of Type Z.

34 Replies

V E L DOP•2y ago

I don't know if it's clear but uh... Basically this was the code I was planning to do, however it tells that some code will never be reached:

    internal T GetAsset<T>(T type, string name) where T : UnityEngine.Object
    {
        UnityEngine.Object result;
        switch(type)
        {
            case AudioClip a:
                result = CachedAudioClips[name];
            break;
            case GameObject go:
                result = CachedPrefabs[name];
            break;
            case Material mat:
                result = CachedMaterials[name];
            break;
            case Mesh mesh:
                result = CachedMeshes[name];
            break;
            case Sprite sprite:
                result = CachedSprites[name];
            break;
            case Texture2D tex:
                result = CachedTextures[name];
            break;
            default:
                throw new ArgumentException("The type of T is not recognized as an UnityEngine.Object class or subclass, or it is not supported.");
        }
        return result as T;
    }

    internal T GetAsset<T>(T type, string name) where T : UnityEngine.Object
    {
        UnityEngine.Object result;
        switch(type)
        {
            case AudioClip a:
                result = CachedAudioClips[name];
            break;
            case GameObject go:
                result = CachedPrefabs[name];
            break;
            case Material mat:
                result = CachedMaterials[name];
            break;
            case Mesh mesh:
                result = CachedMeshes[name];
            break;
            case Sprite sprite:
                result = CachedSprites[name];
            break;
            case Texture2D tex:
                result = CachedTextures[name];
            break;
            default:
                throw new ArgumentException("The type of T is not recognized as an UnityEngine.Object class or subclass, or it is not supported.");
        }
        return result as T;
    }

reflectronic•2y ago

which code is it saying will be unreached

V E L DOP•2y ago

every single case of the switch they are all told as unreachable

reflectronic•2y ago

what is the exact error it tells you

V E L DOP•2y ago

Okay I changed a line and it deleted the error... I don't know what happened but it was telling word for word "this code is unreachable" Although I need to know, can be the argument T type be omitted if it is specified before ? what I did before is that I deleted the T type argument and my switch was switch(default(T)) and there the code was unreachable

reflectronic•2y ago

yes, that will not work null will not match any of them it will always go to default because null is not AudioClip or GameObject or Material

V E L DOP•2y ago

Oh sure.. Oh yeah I see And can the type argument be omitted when T is putted before ? Or not ?

reflectronic•2y ago

what do you mean by "if it's specified before"

V E L DOP•2y ago

Like uh

reflectronic•2y ago

GetAsset<T>(m, x) the <T> can be omitted if m has the type T e.g.

AudioClip a = ...
GetAsset(a, "abc");

AudioClip a = ...
GetAsset(a, "abc");

there is no other circumstance in which the <T> can be omitted

V E L DOP•2y ago

GetAsset<AudioClip>("AnAudioClip")
// equals
GetAsset(AudioClip, "AnAudioClip")

GetAsset<AudioClip>("AnAudioClip")
// equals
GetAsset(AudioClip, "AnAudioClip")

reflectronic•2y ago

no, because those are completely different things

V E L DOP•2y ago

Ahhh

reflectronic•2y ago

T type means "give me a T"

V E L DOP•2y ago

Yeah an instance...

reflectronic•2y ago

"give me an AudioClip"

V E L DOP•2y ago

that's not what I want...

reflectronic•2y ago

i think you will have to give up the switch here

V E L DOP•2y ago

Oh wait if I do new T() ?

reflectronic•2y ago

if (typeof(T) == typeof(AudioClip)) return CachedAudioClips[name];
if (typeof(T) == typeof(GameObject)) return CachedPrefabs[name];
// ...
throw new ArgumentException(...);

if (typeof(T) == typeof(AudioClip)) return CachedAudioClips[name];
if (typeof(T) == typeof(GameObject)) return CachedPrefabs[name];
// ...
throw new ArgumentException(...);

V E L DOP•2y ago

Ah I see Is it possible to give several contraints to where T : new() & where T : UnityEngine.Object sorta ? oh yeah my bad im dumb lol i just had to put a comma Would this work ?

    internal T GetAsset<T>(string name) where T : UnityEngine.Object, new()
    {
        UnityEngine.Object result = new T() switch
        {
            AudioClip => CachedAudioClips[name],
            GameObject => CachedPrefabs[name],
            Material => CachedMaterials[name],
            Mesh => CachedMeshes[name],
            Sprite => CachedSprites[name],
            Texture2D => CachedTextures[name],
            _ => throw new ArgumentException("The type of T is not recognized as an UnityEngine.Object class or subclass, or it is not supported."),
        };
        return result as T;
    }

    internal T GetAsset<T>(string name) where T : UnityEngine.Object, new()
    {
        UnityEngine.Object result = new T() switch
        {
            AudioClip => CachedAudioClips[name],
            GameObject => CachedPrefabs[name],
            Material => CachedMaterials[name],
            Mesh => CachedMeshes[name],
            Sprite => CachedSprites[name],
            Texture2D => CachedTextures[name],
            _ => throw new ArgumentException("The type of T is not recognized as an UnityEngine.Object class or subclass, or it is not supported."),
        };
        return result as T;
    }

reflectronic•2y ago

no, it would not

V E L DOP•2y ago

it's not making any error in my IDE oh...

reflectronic•2y ago

it will make an error when you do GetAsset<Material> or GetAsset<AudioClip>

V E L DOP•2y ago

Ah... That's annoying...

Moods•2y ago

Curious, why’s that?

reflectronic•2y ago

because they do not meet the new() constraint they do not have a public, parameterless constructor it's probably true for other ones too but i didn't check all of them

V E L DOP•2y ago

Ah... I see... Well then I'll do your thing And can't I make a switch(true) { case true when typeof... } ?

reflectronic•2y ago

i suppose you could

V E L DOP•2y ago

Okay alright

V E L DOP•2y ago

Thanks, it does not look to bad

V E L DOP•2y ago

I'll obviously add a check if result is null Ah It will an exception before lol Thanks for help ThumbsUp

JenyaRostov•2y ago

could go even further and maybe do something like

public T GetAsset<T>(string name) where T : UnityEngine.Object
{
    var type = typeof(T);
    if(!CachedAssets.ContainsKey(type))
      throw(...);
    return CachedAssets[type][name];
}

public T GetAsset<T>(string name) where T : UnityEngine.Object
{
    var type = typeof(T);
    if(!CachedAssets.ContainsKey(type))
      throw(...);
    return CachedAssets[type][name];
}

where CachedAssets is

Dictionary<Type,Dictionary<string,UnityEngine.Object>>

Dictionary<Type,Dictionary<string,UnityEngine.Object>>

This way if you have a new asset type you want to cache you just add a key-value pair to CachedAssets dictionary

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ How to make a method returning type T but only taking subclasses of a certain class ?