C# How to build an expression tree for Exists() on a List<T>

Question

List<string> strlist = new List<string> { "one","two", "three" };
string somevalue = "two";

var result = strlist.Exists(e2 => e2 == somevalue);

How to convert the last statement Exists() to an expression tree?

Answer 1

You can create an expression tree from a lambda expression and then compile it into a function that can then be invoked with the strlist and somevalue arguments like this:

var strlist = new List<string> { "one", "two", "three" };
var somevalue = "two";

Expression<Func<List<string>, string, bool>> expression = (list, value) => 
    list.Exists(item => item == value);

Func<List<string>, string, bool> exists = expression.Compile();

bool result = exists(strlist, somevalue);

Or you could do it all in one line, but it's a little hard to read:

var exists = ((Expression<Func<List<string>, string, bool>>)
    ((list, value) => list.Exists(item => item == value))).Compile();

But in the end, isn't it simpler to just do:

bool result = strlist.Contains(somevalue);