如何在预先存在的 class 中的运行时间创建方法？

Question

我正在使用流畅模式来帮助进行单元测试和结果对象构建。流畅的构建器模式的最大痛点是必须为我可能想要设置的每个属性定义所有这些 With____ 方法。

当涉及到我可能想要设置的可能包含 30 个字段的对象时，我并不想写出 30 个几乎都做同样事情的方法。我宁愿只写一些动态的东西来为我处理所有类似的逻辑。

例如（伪代码）

for each property in this.properties 
  define method( property.name with 
    return type: this.class,
    parameter types: [property.type]){

    set property property.name, parameters[0]
    return this
  }

这是我目前在 c#

中的内容

 var properties = typeof(EngineModelBuilder).GetProperties();
 foreach (var property in properties){
   // how do I create a method here with the property?
   // a property has .PropertyType and a .Name
   // and the return type is always going to be 'this'
 }

作为参考，这是正常的流畅构建器方法的外观：

    public EngineModelBuilder WithDescription(string description)
    {
        _description = description;
        return this;
    }

Answer 1

这是我想出的class。它利用 C# 的动态对象来使用运行时间功能的 "method_missing" 方法。

请注意 method_missing 来自 Ruby，通常用于这种动态行为。

DynamicBuilder.cs:

using System;
using System.Collections.Generic;
using System.Dynamic;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;

namespace PGenCore
{
    /// <summary>
    /// TODO: test different field retreival techniques (using fields from T, and managing in a Dictionary)
    ///  - how would we define defaults?
    ///
    ///
    /// Usage:
    ///   dynamic objectBuilder = new ObjectBuilder();
    ///   var object = objectBuilder
    ///     .WithObjectFieldName(appropriateValue)
    ///     .WithObjectField(appropriateValue2)
    ///     .Build();
    ///
    /// </summary>
    /// <typeparam name="T">Type to Build</typeparam>
    public class DynamicBuilder<T> : DynamicObject
    {
        #region List of FieldInformation
        protected FieldInfo[] FieldInfos;
        public FieldInfo[] FieldInformation
        {
            get
            {
                // don't GetFields all the time
                if (FieldInfos != null) return FieldInfos;

                FieldInfos = this.GetType().GetFields(
                    BindingFlags.Public |
                    BindingFlags.NonPublic |
                    BindingFlags.Instance);

                return FieldInfos;
            }
        }
        #endregion

        #region Utility

        /// <summary>
        /// converts FieldName to _fieldName
        /// </summary>
        /// <param name="publicName"></param>
        /// <returns></returns>
        public static string PublicNameToPrivate(string publicName)
        {
            var propertyLowerFirstLetterName = char.ToLower(
                publicName[0]) + publicName.Substring(1);

            var privateName = "_" + propertyLowerFirstLetterName;

            return privateName;
        }
        #endregion

        #region Method is Missing? Check for With{FieldName} Pattern

        /// <summary>
        /// Inherited form DynamicObject.
        /// Ran before each method call.
        ///
        ///
        /// Note: Currently only works for setting one value
        ///  at a time.
        ///   e.g.: instance.Object = value
        /// </summary>
        /// <param name="binder"></param>
        /// <param name="args"></param>
        /// <param name="result"></param>
        /// <returns></returns>
        public override bool TryInvokeMember(
             InvokeMemberBinder binder,
             object[] args,
             out object result)
        {

            var firstArgument = args[0];
            var methodName = binder.Name;
            var propertyRootName = methodName;

            // following the builder pattern,
            // methods that participate in building T,
            // return this so we can chain building methods.
            result = this;

            // for booleans, since the field / property should be named as
            // a question, using "With" doesn't make sense.
            // so, this logic is only needed when we are not setting a
            // boolean field.
            if (!(firstArgument is bool))
            {
                // if we are not setting a bool, and we aren't starting
                // with "With", this method is not part of the
                // fluent builder pattern.
                if (!methodName.Contains("With")) return false;
                propertyRootName = methodName.Replace("With", "");
            }

            // convert to _privateFieldName
            // TODO: think about dynamicly having fields in a Dictionary,
            //  rather than having to specify them
            var builderFieldName = PublicNameToPrivate(propertyRootName);

            // find matching field name, given the method name
            var fieldInfo = FieldInformation
                .FirstOrDefault(
                    field => field.Name == builderFieldName
                 );

            // if the field was not found, abort
            if (fieldInfo == null) return false;

            // set the field to the value in args
            fieldInfo.SetValue(this, firstArgument);
            return true;
        }

        #endregion

        /// <summary>
        /// Returns the built object
        /// </summary>
        /// <returns></returns>
        public virtual T Build()
        {
            throw new NotImplementedException();
        }

        /// <summary>
        /// for any complex associations
        /// - building lists of items
        /// - building anything else that isn't just an easy vavlue.
        /// </summary>
        public virtual void SetRelationshipDefaults()
        {
            throw new NotImplementedException();
        }
    }
}

使用测试可以在这里看到：https://github.com/NullVoxPopuli/Procedural-Builder/blob/master/ProceduralBuilder.Test/DynamicBuilderTest.cs

如何在预先存在的 class 中的 运行 时间创建方法？

How do I create methods at run time in a pre-existing class?

c#

dynamic

如何在预先存在的 class 中的运行时间创建方法？