How to write new List<CustomClass>() in Expression Tree?

Question

I want to know how can we represent below c# code in the expression tree.

var list = new List<CustomClass>(); 
list.add(new CustomClass());

where CustomClass is some complex type class.

Like how an array can be initialized with Expression.NewArrayInit

Thanks

Answer 1

The code that you asked is this:

// List<CustomClass> foo;
var listV = Expression.Variable(typeof(List<CustomClass>), "foo");

// new List<CustomClass>()
var newL = Expression.New(typeof(List<CustomClass>));

// foo = new List<CustomClass>()
var assV = Expression.Assign(listV, newL);

// new CustomClass()
var newEl = Expression.New(typeof(CustomClass));

// foo.Add(new CustomClass())
var addEl = Expression.Call(listV, "Add", null, newEl);

var be = Expression.Block(new[] { listV }, assV, addEl);

Note that I'm giving you a Block Expression... You can put it inside a bigger expression (or create a lambda based on it), but it isn't directly runnable (because it isn't a lambda expression)

An example of lambda expression:

var be = Expression.Block(new[] { listV }, assV, addEl, listV);

var lambda = Expression.Lambda<Func<List<CustomClass>>>(be);
var func = lambda.Compile();

List<CustomClass> res = func();

(note that I'm changing the be variable)