C# object & collection initializers
last modified July 5, 2023
C# object & collection initializers tutorial shows how to initiate objects and collections with initializers.
With object initializers, we can assign values to any accessible fields or properties of an object at creation time without having to invoke a constructor followed by lines of assignment statements. (We cannot use object initializers on records.)
C# object initializer
In the following example, we use an object initializer.
var u1 = new User { FirstName = "John", LastName = "Doe", Occupation = "gardener" };
var u2 = new User { LastName = "Roe", Occupation = "driver", FirstName = "Roger" };
Console.WriteLine(u1);
Console.WriteLine(u2);
class User
{
public string FirstName { get; set; }
public string LastName { get; set; }
public string Occupation { get; set; }
public override string ToString()
{
return $"User {FirstName} {LastName} {Occupation}";
}
}
We create two users utilizing the object initializer syntax.
var u1 = new User { FirstName = "John", LastName = "Doe", Occupation = "gardener" };
We use a pair of {} brackets; the fields are separated with a comma
character.
var u2 = new User { LastName = "Roe", Occupation = "driver", FirstName = "Roger" };
The order of the fields is not relevant.
$ dotnet run User John Doe gardener User Roger Roe driver
C# object initializer with anonymous type
We can create anonymous types with object initializers; this is useful in LINQ expressions.
var u1 = new { FirstName = "John", LastName = "Doe", Occupation = "gardener" };
var u2 = new { FirstName = "Roger", LastName = "Roe", Occupation = "driver" };
Console.WriteLine(u1);
Console.WriteLine(u2);
The example creates two users.
$ dotnet run
{ FirstName = John, LastName = Doe, Occupation = gardener }
{ FirstName = Roger, LastName = Roe, Occupation = driver }
In the next example, we use an anonymous type in a LINQ query expression.
var users = new List<User>
{
new (1, "John", "Doe", "London", "gardener", "2001-04-01", 860),
new (2, "Lenny", "Ferguson", "New York", "programmer", "1997-12-11", 980),
new (3, "Andrew", "Ramos", "Boston", "shop keeper", "1987-02-22", 600),
new (4, "Peter", "Stastny", "Prague", "retired", "1936-03-24", 500),
new (5, "Anna", "Fabry", "Bratislava", "accountant", "1973-11-18", 780),
new (6, "Albert", "Markovic", "Bratislava", "lawyer", "1940-12-11", 1250),
new (7, "Adam", "Palffy", "Trnava", "policeman", "1983-12-01", 890),
new (8, "Robert", "Palkovic", "Bratislava", "veterinary", "1965-05-15", 990),
};
var data = from user in users
select new { user.FirstName, user.LastName, user.Salary };
foreach (var u in data)
{
Console.WriteLine(u);
}
record User(int Id, string FirstName, string LastName, string City,
string Occupation, string DateOfBirth, decimal Salary);
We have a list of users where each user has seven properties. In the LINQ query expression, we generate a list of anonymous types, where each item has only a subset of the properties.
$ dotnet run
{ FirstName = John, LastName = Doe, Salary = 860 }
{ FirstName = Lenny, LastName = Ferguson, Salary = 980 }
{ FirstName = Andrew, LastName = Ramos, Salary = 600 }
{ FirstName = Peter, LastName = Stastny, Salary = 500 }
{ FirstName = Anna, LastName = Fabry, Salary = 780 }
{ FirstName = Albert, LastName = Markovic, Salary = 1250 }
{ FirstName = Adam, LastName = Palffy, Salary = 890 }
{ FirstName = Robert, LastName = Palkovic, Salary = 990 }
C# list initializer
In the following example, we use a list initializer.
var vals = new List<int> { 1, -2, -1, 0, 2, 4, 3, -5 };
var positive = from val in vals
where val > 0
select val;
Console.WriteLine(string.Join(" ", positive));
We have a list of integers. We apply a query expression on the list.
var vals = new List<int> { 1, -2, -1, 0, 2, 4, 3, -5 };
The list collection is initialized in one go; all the elements are specified
within the pair of {} brackets.
$ dotnet run 1 2 4 3
In the next example, we use a list initializer with a User type.
var users = new List<User>
{
new User {FirstName="John", LastName="Doe", Occupation="gardener"},
new User {FirstName="Roger", LastName="Roe", Occupation="driver"},
};
foreach (var user in users)
{
Console.WriteLine(user);
}
class User
{
public string FirstName { get; init; }
public string LastName { get; init; }
public string Occupation { get; init; }
public override string ToString()
{
return $"User {FirstName} {LastName} {Occupation}";
}
}
In this example, we work create a list of users utilizing the list initializer syntax.
$ dotnet run User John Doe gardener User Roger Roe driver
C# Dictionary initializers
Dictionary initializers can be specified in two ways.
var domains = new Dictionary<string, string>
{
{"sk", "Slovakia"},
{"ru", "Russia"},
{"de", "Germany"},
{"no", "Norway"}
};
Console.WriteLine(domains["sk"]);
var days = new Dictionary<string, string>
{
["mo"] = "Monday",
["tu"] = "Tuesday",
["we"] = "Wednesday",
["th"] = "Thursday",
["fr"] = "Friday",
["sa"] = "Saturday",
["su"] = "Sunday"
};
Console.WriteLine(days["fr"]);
The example creates two dictionaries.
var domains = new Dictionary<string, string>
{
{"sk", "Slovakia"},
{"ru", "Russia"},
{"de", "Germany"},
{"no", "Norway"}
};
A new dictionary is created. Between the angle brackets <>,
we specify the data type of the keys and values. New pairs of key/value
elements are written inside nested {} brackets; each pair
is separated by a comma character. For instance, the "sk" key
refers to the "Slovakia" value.
Console.WriteLine(domains["sk"]);
To get a value, we specify the dictionary name followed by square []
brackets. Between the brackets, we specify the key name.
var days = new Dictionary<string, string>
{
["mo"] = "Monday",
["tu"] = "Tuesday",
["we"] = "Wednesday",
["th"] = "Thursday",
["fr"] = "Friday",
["sa"] = "Saturday",
["su"] = "Sunday"
};
This is an alternative syntax; the values are assigned to keys using dictionary access notation.
$ dotnet run Slovakia Friday
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Object and Collection Initializers
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