How to declare a C# Record Type?

Question

I read on a blog that C# 7 will feature record types

class studentInfo(string StudentFName, string StudentMName, string StudentLName);

However

Answer 1

Prior to C# 7.0 you declare classes like this:

Although record types have not been implemented yet in C# 7.0 (as detailed by the other answers), you can shorten your code by using read-only auto-properties, introduced in C# 6.0:

public class studentInfo
{
    public string StudentFName { get; }
    public string StudentMName { get; }
    public string StudentLName { get; }

    public studentInfo(string strFN, string strMN, string strLN)
    {
        StudentFName = strFN;
        StudentMName = strMN;
        StudentLName = strLN;
    }
}

Answer 2

C#9 is now available and records with it.

Here are some example:

public record Person
{
    public string LastName { get; init; }
    public string FirstName { get; init; }

    public Person(string first, string last) => (FirstName, LastName) = (first, last);
}

With the use of positional records (and inheritance):

public record Teacher(string FirstName, string LastName,
    string Subject)
    : Person(FirstName, LastName);

public sealed record Student(string FirstName,
    string LastName, int Level)
    : Person(FirstName, LastName);

var person = new Person("Bill", "Wagner");

var (first, last) = person;
Console.WriteLine(first);
Console.WriteLine(last);

Finally, records support with-expressions. A with-expression instructs the compiler to create a copy of a record, but with specified properties modified:

Person brother = person with { FirstName = "Paul" };

Everything you need to know about every new features including records here

Answer 3

Update:

C# 9 now contains record types.

public record Person
{
    public string LastName { get; }
    public string FirstName { get; }

    public Person(string first, string last) => (FirstName, LastName) = (first, last);
}

Old answer:

Record types are not (yet) implemented in C#. See the proposal in the official GitHub repository:

https://github.com/dotnet/csharplang/blob/master/proposals/records.md

Discuss or vote at https://github.com/dotnet/csharplang/issues/39

Answer 4

[Rewritten to reflect the current state of things]

To add to the other answers, you can easily track when C# features are pencilled in to appear in C# these days. For example, the Champion "Records" issue shows the state of thinking around records. Records is now scheduled for C# 9. But that feature was previously touted for C# 6, C# 7 and C# 8 too, so it remains only an aspiration.

Answer 5

There is a way if you're looking for record-like, lazy way of implementing constructors using currently available C# 7 functionality:

class Lazystructor
{
    int a;
    float b;
    WebClient c;

    public Lazystructor(int a, float b, WebClient c)
        =>  (this.a, this.b, this.c) = (a, b, c);
}

A bit of consideration if you're using this on a performance-sensitive scenario, as it's a process of ValueTuple creation and extraction.

Answer 6

Record types were on the roadmap for C# 7.0, but were ultimately delayed until a later version of the language.

To quote Mads Torgersen in reply to this blog post,

[Primary constructors] are still on the radar, along with the related concept of record types (which we considered for C# 7.0), and I am hopeful that we can land on a better design – maybe one that encompasses both.

As of C# 7's release, the GitHub proposal for this language feature still indicates that the implementation is "In Progress."