---
lang: ja-jp
breaks: true
---
# C# `Func`デリゲート型を動的に生成する方法 2021-10-31

## 力技による生成

public class DynamicFunc
{
    static ExpressionMethodCache<DynamicFunc> s_methodCache;

    static DynamicFunc()
    {
        s_methodCache = new();
    }

    private static Func<TResult> Create<TResult>()
    {
        return new Func<TResult>(() => default(TResult));
    }
    private static Func<T1, TResult> Create<T1, TResult>()
    {
        return new Func<T1, TResult>((t1) => default(TResult));
    }
    private static Func<T1, T2, TResult> Create<T1, T2, TResult>()
    {
        return new Func<T1, T2, TResult>((t1, t2) => default(TResult));
    }
    private static Func<T1, T2, T3, TResult> Create<T1, T2, T3, TResult>()
    {
        return new Func<T1, T2, T3, TResult>((t1, t2, t3) => default(TResult));
    }
    private static Func<T1, T2, T3, T4, TResult> Create<T1, T2, T3, T4, TResult>()
    {
        return new Func<T1, T2, T3, T4, TResult>((t1, t2, t3, t4) => default(TResult));
    }
    private static Func<T1, T2, T3, T4, T5, TResult> Create<T1, T2, T3, T4, T5, TResult>()
    {
        return new Func<T1, T2, T3, T4, T5, TResult>((t1, t2, t3, t4, t5) => default(TResult));
    }
    private static Func<T1, T2, T3, T4, T5, T6, TResult> Create<T1, T2, T3, T4, T5, T6, TResult>()
    {
        return new Func<T1, T2, T3, T4, T5, T6, TResult>((t1, t2, t3, t4, t5, t6) => default(TResult));
    }
    private static Func<T1, T2, T3, T4, T5, T6, T7, TResult> Create<T1, T2, T3, T4, T5, T6, T7, TResult>()
    {
        return new Func<T1, T2, T3, T4, T5, T6, T7, TResult>((t1, t2, t3, t4, t5, t6, t7) => default(TResult));
    }
    private static Func<T1, T2, T3, T4, T5, T6, T7, T8, TResult> Create<T1, T2, T3, T4, T5, T6, T7, T8, TResult>()
    {
        return new Func<T1, T2, T3, T4, T5, T6, T7, T8, TResult>((t1, t2, t3, t4, t5, t6, t7, t8) => default(TResult));
    }
    private static Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, TResult> Create<T1, T2, T3, T4, T5, T6, T7, T8, T9, TResult>()
    {
        return new Func<T1, T2, T3, T4, T5, T6, T7, T8, T9, TResult>((t1, t2, t3, t4, t5, t6, t7, t8, t9) => default(TResult));
    }

    public static object Create(Type[] types, Type result)
    {
        Type[] genericTypeArguments = null;
        if (types != null)
        {
            genericTypeArguments = types.Concat(new Type[] { result }).ToArray();
        }
        else if (result != null)
        {
            genericTypeArguments = new Type[] { result };
        }
        else
        {
            throw new ArgumentException($"The parameter to generate the {nameof(Func<object>)} delegate has not been specified.");
        }

        Type[] parameters = null;
        string methodName = nameof(Create);

        // キャッシュ機構を備えた、式木による生成。
        Delegate func = s_methodCache.GetMethod_Static(
            genericTypeArguments,
            parameters,
            methodName
            );
        return func.DynamicInvoke();
    }
}

###### tags: `C#` `Func` `リフレクション` `式木` `動的生成`