.NET 6 LINQ Improvements - Default Values

A Cleaner Way to Specify Default Values

In the APIs for System.Linq.Enumerable and System.Linq.Queryable we have overloads for FirstAsync(), SingleAsync() and LastAsync() (and their synchronous counterparts) that return the first, single or last element of a sequence. If they find nothing, then they throw an exception.

When this behaviour is not desired, our other option is to use SingleOrDefaultAsync(), FirstOrDefaultAsync(), LastOrDefaultAsync(), where instead of an exception, the a default(T) value is returned. For example, the default for an int is 0 and the default for a string is null.

We do already have control over the default value, but it is not very convenient to use:

var singleOrDefault = list.Where(x => x.Age > 20)
    .DefaultIfEmpty(new Person
    {
        Age = 99,
        Name = "Nobody"
    })
    .Single();

.NET 6 introduces new overloads that allows us to specify the default value more succinctly. For example:

var singleOrDefault = list.SingleOrDefault(x => x.Age > 100, new Person
{
    Age = 99,
    Name = "Nobody"
});