Custom class serialization without default constructor does not work

Describe the bug Custom class serialization without default constructor does not work

To Reproduce Steps to reproduce the behavior:

    [ServerRpc]
    public void TestServerRCP(Foo foo)
    {
    // foo is null
    }

    public class Foo : INetworkSerializable
    {
        public string Boo;
        public string Poo;

        public Foo(string boo, string poo)
        {
            Boo = boo;
            Poo = poo;
        }

        /// <inheritdoc />
        public void NetworkSerialize(NetworkSerializer serializer)
        {
            serializer.Serialize(ref Boo);
            serializer.Serialize(ref Poo);
        }
    }

Actual outcome Foo is null

Expected outcome

• Provided constructor should be used instead, (if possible) or exception should be returned
• Exception should be returned that the default constructor is missing.
• Allow for custom constructors in serializer API

Environment (please complete the following information):

• OS: Windows 10
• Unity Version: 2020.3.5f1
• MLAPI Version: 1.0.0

[ArgentumVir]

In case its useful to anyone else, in this thread (and the current documentation) the term default constructor is being used to refer to a parameterless constructor (this messed me up when googling a bit). To elaborate unnecessarily, this constructor only exists if you have explicitly defined it or you have defined no constructors (and so the default constructor given to you is a parameterless one)

tldr; In short, your receiver will receive null instead of the value you expect if no parameterless constructor is provided in the class you are trying to serialize.

Gratuitous examples for those who only read code and are allergic to text:

✔️ The following will serialize properly (C# gives you a default constructor since you didn’t declare any constructors at all and this default constructor is parameterless)

using MLAPI.Serialization;

public class Example : INetworkSerializable
{
    public int SomeVariable;

    public void NetworkSerialize(NetworkSerializer serializer)
    {
        serializer.Serialize(ref SomeVariable);
    }
}

❌ The following will NOT serialize properly, the receiver will just get null because you have defined a constructor with parameters, so C# will not give you a default one (which would have been parameterless)

using MLAPI.Serialization;

public class Example : INetworkSerializable
{
    public int SomeVariable;

    public void NetworkSerialize(NetworkSerializer serializer)
    {
        serializer.Serialize(ref SomeVariable);
    }

    public Example(int someVariable)
    {
        SomeVariable = someVariable;
    }
}

✔️ The following will serialize properly because a parameterless constructor was explicitly declared on the class

using MLAPI.Serialization;

public class Example : INetworkSerializable
{
    public int SomeVariable;

    public void NetworkSerialize(NetworkSerializer serializer)
    {
        serializer.Serialize(ref SomeVariable);
    }

    // You need this parameterless constructor for serialization to not return null
    public Example()
    {
    }

    public Example(int someVariable)
    {
        SomeVariable = someVariable;
    }
}

[ThusSpokeNomad]

@ShadauxCat, not urgent and also not triaged yet but I think it’d worth checking if we implemented RPC params new() (default parameterless constructor) constraint check on the ILPP side and closing this one off. There might be a minor update on the docs side (as we mentioned before above) but I actually want to just leave all this on your judgement.