UniVRM/Assets/UniGLTF/Runtime/UniJSON/FormatterExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Linq;
using System.Reflection;


namespace UniJSON
{
    public static partial class FormatterExtensions
    {
        public static ArraySegment<Byte> GetStoreBytes(this IFormatter f)
        {
            return f.GetStore().Bytes;
        }

        public static void Key(this IFormatter f, string x)
        {
            f.Key(Utf8String.From(x));
        }

        public static void Value(this IFormatter f, IEnumerable<byte> raw, int count)
        {
            f.Value(new ArraySegment<byte>(raw.Take(count).ToArray()));
        }

        public static void Value(this IFormatter f, Byte[] bytes)
        {
            f.Value(new ArraySegment<Byte>(bytes));
        }

#if UNITY_5_6_OR_NEWER
        public static void Value(this IFormatter f, UnityEngine.Vector2 v)
        {
            //CommaCheck();
            f.BeginMap(2);
            f.Key("x"); f.Value(v.x);
            f.Key("y"); f.Value(v.y);
            f.EndMap();
        }

        public static void Value(this IFormatter f, UnityEngine.Vector3 v)
        {
            //CommaCheck();
            f.BeginMap(3);
            f.Key("x"); f.Value(v.x);
            f.Key("y"); f.Value(v.y);
            f.Key("z"); f.Value(v.z);
            f.EndMap();
        }

        public static void Value(this IFormatter f, UnityEngine.Vector4 v)
        {
            //CommaCheck();
            f.BeginMap(4);
            f.Key("x"); f.Value(v.x);
            f.Key("y"); f.Value(v.y);
            f.Key("z"); f.Value(v.z);
            f.Key("w"); f.Value(v.w);
            f.EndMap();
        }
#endif

        static MethodInfo GetMethod<T>(Expression<Func<T>> expression)
        {
            var method = typeof(FormatterExtensions).GetMethod("Serialize");
            return method.MakeGenericMethod(typeof(T));
        }

        //
        // https://stackoverflow.com/questions/238765/given-a-type-expressiontype-memberaccess-how-do-i-get-the-field-value
        //
        public static void KeyValue<T>(this IFormatter f, Expression<Func<T>> expression)
        {
            // lambda body
            var lambdaBody = (MemberExpression)expression.Body;

            if (lambdaBody.Expression.NodeType == ExpressionType.Constant)
            {
                // 
                // KeyValue(() => Field);
                // 
                var constant = (ConstantExpression)lambdaBody.Expression;
                var field = (FieldInfo)lambdaBody.Member;
                var value = field.GetValue(constant.Value);
                if (value != null)
                {
                    f.Key(lambdaBody.Member.Name);
                    f.Serialize(value);
                }
            }
            else
            {
                // 
                // KeyValue(() => p.Field);
                // 
                var capture = (MemberExpression)lambdaBody.Expression;

                var captureVariable = (ConstantExpression)capture.Expression;
                var captureObj = captureVariable.Value;
                var captureField = (FieldInfo)capture.Member;
                var captureValue = captureField.GetValue(captureObj);

                var field = (FieldInfo)lambdaBody.Member;

                var value = field.GetValue(captureValue);
                if (value != null)
                {
                    f.Key(field.Name);
                    f.Serialize(value);
                }
            }
        }
    }
}