功能“递归模式”在 C# 7.3 中不可用，请使用 8.0 或更高的语言版本的一种兼容处理方案

原程序：

internal class ControllerParameterCreator : IParameterCreator
{
    private Controller controller;

    public ControllerParameterCreator(Controller controller)
    {
        this.controller = controller;
    }

    public Parameter CreateSystem(string name, int unused)
    {
        return ParameterInfoProvider.GetType(name) switch
        {
            PrimitiveType.Double => new ControllerParameter<double>(controller, name, PrimitiveType.Double),
            PrimitiveType.Integer => new ControllerParameter<int>(controller, name, PrimitiveType.Integer),
            PrimitiveType.Long => new ControllerParameter<long>(controller, name, PrimitiveType.Long),
            PrimitiveType.Single => new ControllerParameter<float>(controller, name, PrimitiveType.Single),
            PrimitiveType.String => new ControllerParameter<string>(controller, name, PrimitiveType.String),
            _ => null,
        };
    }

    public Parameter CreateAxis(string name, int index)
    {
        return ParameterInfoProvider.GetType(name) switch
        {
            PrimitiveType.Double => new ControllerParameter<double>(controller, name, PrimitiveType.Double, ParameterContext.Axis, index),
            PrimitiveType.Integer => new ControllerParameter<int>(controller, name, PrimitiveType.Integer, ParameterContext.Axis, index),
            PrimitiveType.Long => new ControllerParameter<long>(controller, name, PrimitiveType.Long, ParameterContext.Axis, index),
            PrimitiveType.Single => new ControllerParameter<float>(controller, name, PrimitiveType.Single, ParameterContext.Axis, index),
            PrimitiveType.String => new ControllerParameter<string>(controller, name, PrimitiveType.String, ParameterContext.Axis, index),
            _ => null,
        };
    }

    public Parameter CreateTask(string name, int task)
    {
        return ParameterInfoProvider.GetType(name) switch
        {
            PrimitiveType.Double => new ControllerParameter<double>(controller, name, PrimitiveType.Double, ParameterContext.Task, task),
            PrimitiveType.Integer => new ControllerParameter<int>(controller, name, PrimitiveType.Integer, ParameterContext.Task, task),
            PrimitiveType.Long => new ControllerParameter<long>(controller, name, PrimitiveType.Long, ParameterContext.Task, task),
            PrimitiveType.Single => new ControllerParameter<float>(controller, name, PrimitiveType.Single, ParameterContext.Task, task),
            PrimitiveType.String => new ControllerParameter<string>(controller, name, PrimitiveType.String, ParameterContext.Task, task),
            _ => null,
        };
    }
}

处理后程序：

internal class ControllerParameterCreator : IParameterCreator
{
    private Controller controller;

    public ControllerParameterCreator(Controller controller)
    {
        this.controller = controller;
    }

    public Parameter CreateSystem(string name, int unused)
    {
#if CSHARP_8_OR_NEWER
        // C# 8.0+ 递归模式写法
        return ParameterInfoProvider.GetType(name) switch
        {
            PrimitiveType.Double => new ControllerParameter<double>(controller, name, PrimitiveType.Double),
            PrimitiveType.Integer => new ControllerParameter<int>(controller, name, PrimitiveType.Integer),
            PrimitiveType.Long => new ControllerParameter<long>(controller, name, PrimitiveType.Long),
            PrimitiveType.Single => new ControllerParameter<float>(controller, name, PrimitiveType.Single),
            PrimitiveType.String => new ControllerParameter<string>(controller, name, PrimitiveType.String),
            _ => null,
        };
#else
        // C# 7.3 传统 switch 写法
        PrimitiveType type = ParameterInfoProvider.GetType(name);
        switch (type)
        {
            case PrimitiveType.Double:
                return new ControllerParameter<double>(controller, name, PrimitiveType.Double);
            case PrimitiveType.Integer:
                return new ControllerParameter<int>(controller, name, PrimitiveType.Integer);
            case PrimitiveType.Long:
                return new ControllerParameter<long>(controller, name, PrimitiveType.Long);
            case PrimitiveType.Single:
                return new ControllerParameter<float>(controller, name, PrimitiveType.Single);
            case PrimitiveType.String:
                return new ControllerParameter<string>(controller, name, PrimitiveType.String);
            default:
                return null;
        }
#endif
    }

    public Parameter CreateAxis(string name, int index)
    {
#if CSHARP_8_OR_NEWER
        return ParameterInfoProvider.GetType(name) switch
        {
            PrimitiveType.Double => new ControllerParameter<double>(controller, name, PrimitiveType.Double, ParameterContext.Axis, index),
            PrimitiveType.Integer => new ControllerParameter<int>(controller, name, PrimitiveType.Integer, ParameterContext.Axis, index),
            PrimitiveType.Long => new ControllerParameter<long>(controller, name, PrimitiveType.Long, ParameterContext.Axis, index),
            PrimitiveType.Single => new ControllerParameter<float>(controller, name, PrimitiveType.Single, ParameterContext.Axis, index),
            PrimitiveType.String => new ControllerParameter<string>(controller, name, PrimitiveType.String, ParameterContext.Axis, index),
            _ => null,
        };
#else
        PrimitiveType type = ParameterInfoProvider.GetType(name);
        switch (type)
        {
            case PrimitiveType.Double:
                return new ControllerParameter<double>(controller, name, PrimitiveType.Double, ParameterContext.Axis, index);
            case PrimitiveType.Integer:
                return new ControllerParameter<int>(controller, name, PrimitiveType.Integer, ParameterContext.Axis, index);
            case PrimitiveType.Long:
                return new ControllerParameter<long>(controller, name, PrimitiveType.Long, ParameterContext.Axis, index);
            case PrimitiveType.Single:
                return new ControllerParameter<float>(controller, name, PrimitiveType.Single, ParameterContext.Axis, index);
            case PrimitiveType.String:
                return new ControllerParameter<string>(controller, name, PrimitiveType.String, ParameterContext.Axis, index);
            default:
                return null;
        }
#endif
    }

    public Parameter CreateTask(string name, int task)
    {
#if CSHARP_8_OR_NEWER
        return ParameterInfoProvider.GetType(name) switch
        {
            PrimitiveType.Double => new ControllerParameter<double>(controller, name, PrimitiveType.Double, ParameterContext.Task, task),
            PrimitiveType.Integer => new ControllerParameter<int>(controller, name, PrimitiveType.Integer, ParameterContext.Task, task),
            PrimitiveType.Long => new ControllerParameter<long>(controller, name, PrimitiveType.Long, ParameterContext.Task, task),
            PrimitiveType.Single => new ControllerParameter<float>(controller, name, PrimitiveType.Single, ParameterContext.Task, task),
            PrimitiveType.String => new ControllerParameter<string>(controller, name, PrimitiveType.String, ParameterContext.Task, task),
            _ => null,
        };
#else
        PrimitiveType type = ParameterInfoProvider.GetType(name);
        switch (type)
        {
            case PrimitiveType.Double:
                return new ControllerParameter<double>(controller, name, PrimitiveType.Double, ParameterContext.Task, task);
            case PrimitiveType.Integer:
                return new ControllerParameter<int>(controller, name, PrimitiveType.Integer, ParameterContext.Task, task);
            case PrimitiveType.Long:
                return new ControllerParameter<long>(controller, name, PrimitiveType.Long, ParameterContext.Task, task);
            case PrimitiveType.Single:
                return new ControllerParameter<float>(controller, name, PrimitiveType.Single, ParameterContext.Task, task);
            case PrimitiveType.String:
                return new ControllerParameter<string>(controller, name, PrimitiveType.String, ParameterContext.Task, task);
            default:
                return null;
        }
#endif
    }
}

关键实现说明

1. 条件编译符号

   • 使用 #if CSHARP_8_OR_NEWER 和 #else 隔离不同版本的语法。

   • 需在项目文件中定义符号（见下方配置步骤）。

2. 版本差异处理

   • C# 8.0+ ：使用简洁的递归模式匹配（switch 表达式）。

   • C# 7.3 ：回退到传统的 switch-case 语句。

3. 功能一致性

   两种写法的逻辑完全一致，仅语法形式不同。

---

项目配置步骤

1. 定义编译符号

   在 .csproj 文件中根据语言版本自动设置符号：

<PropertyGroup>
  <!-- 当使用 C# 8.0+ 时自动定义符号 -->
  <DefineConstants Condition="'$(LangVersion)' >= '8.0'">CSHARP_8_OR_NEWER</DefineConstants>
</PropertyGroup>

手动指定版本（可选）

若需强制兼容性，可手动设置语言版本：

<PropertyGroup>
  <LangVersion>7.3</LangVersion> <!-- 或 8.0、latest 等 -->
</PropertyGroup>

优点

• 无缝适配：根据项目语言版本自动选择最优语法。

• 维护友好：升级到 C# 8.0+ 时无需修改代码，直接享受新语法。

• 编译安全：避免因版本不兼容导致的编译错误。