إنشاء التعبيرات يدويًا

إنشاء الأشجار يدويًا

using System;
using System.Linq.Expressions;

var five = Expression.Constant(5);
Console.WriteLine(five);          // 5
Console.WriteLine(five.Type);     // System.Int32

Expression.Parameter

using System;
using System.Linq.Expressions;

var x = Expression.Parameter(typeof(int), "x");
Console.WriteLine(x.Name + " : " + x.Type); // x : System.Int32

Expression.Constant

using System;
using System.Linq.Expressions;

var c = Expression.Constant(42);
var typed = Expression.Constant(3.14, typeof(double));
Console.WriteLine(c + " " + typed); // 42 3.14

Expression.Add

using System;
using System.Linq.Expressions;

var x = Expression.Parameter(typeof(int), "x");
var sum = Expression.Add(x, Expression.Constant(1));
Console.WriteLine(sum); // (x + 1)

عوامل ثنائية أخرى

using System;
using System.Linq.Expressions;

var x = Expression.Parameter(typeof(int), "x");
var gt = Expression.GreaterThan(x, Expression.Constant(10));
var mul = Expression.Multiply(x, Expression.Constant(2));
Console.WriteLine(gt + " | " + mul); // (x > 10) | (x * 2)

تغليف التعبير في Lambda

using System;
using System.Linq.Expressions;

var x = Expression.Parameter(typeof(int), "x");
var body = Expression.Add(x, Expression.Constant(1));
var lambda = Expression.Lambda<Func<int, int>>(body, x);
Console.WriteLine(lambda); // x => (x + 1)

تركيب التعبيرات المتداخلة

using System;
using System.Linq.Expressions;

var x = Expression.Parameter(typeof(int), "x");
var addOne = Expression.Add(x, Expression.Constant(1));
var timesTwo = Expression.Multiply(addOne, Expression.Constant(2));
Console.WriteLine(timesTwo); // ((x + 1) * 2)

الوصول إلى الأعضاء

using System;
using System.Linq.Expressions;

var s = Expression.Parameter(typeof(string), "s");
var lengthAccess = Expression.Property(s, "Length");
Console.WriteLine(lengthAccess); // s.Length

استدعاءات الأساليب

using System;
using System.Linq.Expressions;

var s = Expression.Parameter(typeof(string), "s");
var toUpper = typeof(string).GetMethod("ToUpper", Type.EmptyTypes);
var call = Expression.Call(s, toUpper);
Console.WriteLine(call); // s.ToUpper()

التحقق من الأنواع أثناء الإنشاء

using System;
using System.Linq.Expressions;

try {
    var bad = Expression.Add(
        Expression.Constant(1),
        Expression.Constant("text")); // int + string
} catch (InvalidOperationException) {
    Console.WriteLine("type mismatch rejected");
}

تجميع المفاهيم

using System;
using System.Linq.Expressions;

var x = Expression.Parameter(typeof(int), "x");
var body = Expression.Multiply(
    Expression.Add(x, Expression.Constant(1)),
    Expression.Constant(2));
var lambda = Expression.Lambda<Func<int, int>>(body, x);
Console.WriteLine(lambda); // x => ((x + 1) * 2)

اختبار سريع

مراجعة