生成代码，从 T 到 T1, T2, Tn —— 自动生成多个类型的泛型

public class Demo<T>
{
    public Demo(Action<T> demo)
    {
        _demo = demo ?? throw new ArgumentNullException(nameof(action));
    }

    private Action<T> _demo;

    public async Task<T> DoAsync(T t)
    {
        // 做某些事情。
    }

    // 做其他事情。
}

public class Demo<T1, T2>
{
    public Demo(Action<T1, T2> demo)
    {
        _demo = demo ?? throw new ArgumentNullException(nameof(action));
    }

    private Action<T1, T2> _demo;

    public async Task<(T1, T2)> DoAsync(T1 t1, T2 t2)
    {
        // 做某些事情。
    }

    // 做其他事情。
}

using System;
using System.Linq;
using static System.Environment;

namespace Walterlv.BuildTools
{
    public class GenericTypeGenerator
    {
        private static readonly string GeneratedHeader =
$@"//------------------------------------------------------------------------------
// <auto-generated>
//     此代码由工具生成。
//     运行时版本:{Environment.Version.ToString(4)}
//
//     对此文件的更改可能会导致不正确的行为，并且如果
//     重新生成代码，这些更改将会丢失。
// </auto-generated>
//------------------------------------------------------------------------------

#define GENERATED_CODE
";

        private static readonly string GeneratedFooter =
            $@"";

        private readonly string _genericTemplate;
        private readonly string _toolName;

        public GenericTypeGenerator(string toolName, string genericTemplate)
        {
            _toolName = toolName ?? throw new ArgumentNullException(nameof(toolName));
            _genericTemplate = genericTemplate ?? throw new ArgumentNullException(nameof(toolName));
        }

        public string Generate(int genericCount)
        {
            var toolName = _toolName;
            var toolVersion = "1.0";
            var GeneratedAttribute = $"[System.CodeDom.Compiler.GeneratedCode(\"{toolName}\", \"{toolVersion}\")]";

            var content = _genericTemplate
                // 替换泛型。
                .Replace("<out T>", FromTemplate("<{0}>", "out T{n}", ", ", genericCount))
                .Replace("Task<T>", FromTemplate("Task<({0})>", "T{n}", ", ", genericCount))
                .Replace("Func<T, Task>", FromTemplate("Func<{0}, Task>", "T{n}", ", ", genericCount))
                .Replace(" T, Task>", FromTemplate(" {0}, Task>", "T{n}", ", ", genericCount))
                .Replace("(T, bool", FromTemplate("({0}, bool", "T{n}", ", ", genericCount))
                .Replace("var (t, ", FromTemplate("var ({0}, ", "t{n}", ", ", genericCount))
                .Replace(", t)", FromTemplate(", {0})", "t{n}", ", ", genericCount))
                .Replace("return (t, ", FromTemplate("return ({0}, ", "t{n}", ", ", genericCount))
                .Replace("<T>", FromTemplate("<{0}>", "T{n}", ", ", genericCount))
                .Replace("(T value)", FromTemplate("(({0}) value)", "T{n}", ", ", genericCount))
                .Replace("(T t)", FromTemplate("({0})", "T{n} t{n}", ", ", genericCount))
                .Replace("(t)", FromTemplate("({0})", "t{n}", ", ", genericCount))
                .Replace("var t =", FromTemplate("var ({0}) =", "t{n}", ", ", genericCount))
                .Replace(" T ", FromTemplate(" ({0}) ", "T{n}", ", ", genericCount))
                .Replace(" t;", FromTemplate(" ({0});", "t{n}", ", ", genericCount))
                // 生成 [GeneratedCode]。
                .Replace("    public interface ", $"    {GeneratedAttribute}{NewLine}    public interface ")
                .Replace("    public class ", $"    {GeneratedAttribute}{NewLine}    public class ")
                .Replace("    public sealed class ", $"    {GeneratedAttribute}{NewLine}    public sealed class ");
            return GeneratedHeader + NewLine + content.Trim() + NewLine + GeneratedFooter;
        }

        private static string FromTemplate(string template, string part, string separator, int count)
        {
            return string.Format(template,
                string.Join(separator, Enumerable.Range(1, count).Select(x => part.Replace("{n}", x.ToString()))));
        }
    }
}

using System.IO;
using System.Linq;
using System.Text;
using Walterlv.BuildTools;

class Program
{
    static void Main(string[] args)
    {
        foreach (var argument in args)
        {
            GenerateGenericTypes(argument, 4);
        }
    }

    private static void GenerateGenericTypes(string file, int count)
    {
        // 读取原始文件并创建泛型代码生成器。
        var template = File.ReadAllText(file, Encoding.UTF8);
        var generator = new GenericTypeGenerator(template);

        // 根据泛型个数生成目标文件路径和文件内容。
        var format = GetIndexedFileNameFormat(file);
        (string targetFileName, string targetFileContent)[] contents = Enumerable.Range(2, count - 1).Select(i =>
            (string.Format(format, i), generator.Generate(i))
        ).ToArray();

        // 写入目标文件。
        foreach (var writer in contents)
        {
            File.WriteAllText(writer.targetFileName, writer.targetFileContent);
        }
    }

    private static string GetIndexedFileNameFormat(string fileName)
    {
        var directory = Path.GetDirectoryName(fileName);
        var name = Path.GetFileNameWithoutExtension(fileName);
        if (name.EndsWith("1"))
        {
            name = name.Substring(0, name.Length - 1);
        }

        return Path.Combine(directory, name + "{0}.cs");
    }
}

"$(ProjectDir)..\CodeGenerator\$(OutDir)net47\CodeGenerator.exe" "$(ProjectDir)..\Walterlv.Demo\Generic\IDemoFile.cs" "$(ProjectDir)..\..\Walterlv.Demo\Generic\DemoFile.cs"