mardi 24 novembre 2020

Searching for a more elegant way to turn a MethodInfo to a Func through Expressions

I have the following code:

       public static Func<object[], object> CreateStaticFunc(this MethodInfo methodInfo)
    {
        var types = methodInfo.GetParameters().Select(p => p.ParameterType);



        if (methodInfo.ReturnType.Equals((typeof(void))))
        {
            Debug.LogError("Cannot create a Func from a method without a return type!");
            return null;
        }

        if (!methodInfo.IsStatic)
        {
            Debug.LogError("Cannot create a static Func from a non-static function!");
            return null;
        }

        var funcParams = methodInfo.GetParameters();

        var input = Expression.Parameter(typeof(object[]), "input");

        Func<object[], object> returned = null;

        //TODO research how to make this cleaner.
        switch (funcParams.Length)
        {
            case 0:
                returned = Expression.Lambda<Func<object[], object>>(Expression.Call(methodInfo), input).Compile();
                break;
            case 1:
                returned = Expression.Lambda<Func<object[], object>>(Expression.Call(methodInfo, 
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(0)), funcParams[0].ParameterType)), input).Compile();
                break;
            case 2:
                returned = Expression.Lambda<Func<object[], object>>(Expression.Call(methodInfo,
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(0)), funcParams[0].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(1)), funcParams[1].ParameterType)), input).Compile();
                break;
            case 3:
                returned = Expression.Lambda<Func<object[], object>>(Expression.Call(methodInfo,
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(0)), funcParams[0].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(1)), funcParams[1].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(2)), funcParams[2].ParameterType)), input).Compile();
                break;
            case 4:
                returned = Expression.Lambda<Func<object[], object>>(Expression.Call(methodInfo,
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(0)), funcParams[0].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(1)), funcParams[1].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(2)), funcParams[2].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(3)), funcParams[3].ParameterType)), input).Compile();
                break;
            case 5:
                returned = Expression.Lambda<Func<object[], object>>(Expression.Call(methodInfo,
                   Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(0)), funcParams[0].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(1)), funcParams[1].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(2)), funcParams[2].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(3)), funcParams[3].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(4)), funcParams[4].ParameterType)), input).Compile();
                break;
            case 6:
                returned = Expression.Lambda<Func<object[], object>>(Expression.Call(methodInfo,
                   Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(0)), funcParams[0].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(1)), funcParams[1].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(2)), funcParams[2].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(3)), funcParams[3].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(4)), funcParams[4].ParameterType),
                    Expression.Convert(Expression.ArrayAccess(input, Expression.Constant(5)), funcParams[5].ParameterType)), input).Compile();
                break;
        }
       

        return returned;
    }

}

This turns the MethodInfo into a Func/delegate so that it may be cached to improve performance since MethodInfo.Invoke is not very performant.

The code seems to work, but I cannot write a more elegant/concise way of doing this since I do not know the number of parameters ahead of time.

Can anyone help with this? Is it even possible?





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