Question

I know that Lambda Expressions is not just for LINQ. But what are the possible scenarios which we can use Lambda Expression in? what is the code of these examples without Lambda Expression?

Answer 1

Let’s say you have a list of Person objects and want to make a Dictionary<int, string> out of it to be able to look up person’s name by his SSN or something.

With ToDictionary method it’s easy:

var dictionary = Persons.ToDictionary(p => p.SSN, p => p.Name);

The alternative is to create a dictionary and then use a foreach loop:

var dictionary = new Dictionary<int, string>();
foreach (Person p in Persons) {
    dictionary.Add(p.SSN, p.Name);
} 

Which is kinda wordy and hides the intent.

You can use ToDictionary but without lambda expressions:

var dictionary = Persons.ToDictionary(GetPersonKey, GetPersonValue);

//....

int GetPersonKey(Person p) {
    return p.SSN;
} 

string GetPersonValue(Person p) {
    return p.Name;
}

which is obviously not so concise.

You could go with anonymous delegates:

var dictionary = Persons.ToDictionary(delegate(Person p) { return p.SSN; },                                 
                                      delegate(Person p) { return p.Name; });

but it doesn’t compare with lambda expressions in conciseness.

I wouldn’t want to use any LINQ extension methods if lambda expressions weren’t implemented in the language because it would requite a lot of unnecessary code.