c# switch keyword used in a different way than I have seen before-CodePudding

This is a use of the switch keyword which I have not seen before:

public TestUserType UserType { get; private set; } = TestUserType.None;

public override Task<AuthenticationState> GetAuthenticationStateAsync()
        {
            var task = this.UserType switch
            {
                TestUserType.Admin => Task.FromResult(new AuthenticationState(this.Admin)),
                TestUserType.User => Task.FromResult(new AuthenticationState(this.User)),
                TestUserType.None => Task.FromResult(new AuthenticationState(this.Anonymous)),
                _ => Task.FromResult(new AuthenticationState(this.Visitor))
            };
            return task;
        }

Can someone explain this use of 'switch'? I checked the docs, but I only found the usual switch (var) usage.

CodePudding user response：

This is known as a switch expression. Unlike the traditional switch statements, switch expressions return a value.

Furthermore, they support concepts such as pattern matching which is a far more expressive syntax than (used to be) allowed by traditional case statements. But as Hans points out below, the switch statement also supports pattern matching.

CodePudding user response：

Equivalent in old notation:

    switch(UserType)
    {
        case TestUserType.Admin: 
            return Task.FromResult(new AuthenticationState(this.Admin));
        case TestUserType.User:
            return Task.FromResult(new AuthenticationState(this.User));
        case TestUserType.None:
            return Task.FromResult(new AuthenticationState(this.Anonymous));
        default:
            return Task.FromResult(new AuthenticationState(this.Visitor));        
    }