Lazy

Helpers for lazy initialization in .NET applications.

SyncLazy

SyncLazy is System.Lazy<T> wrapper which re-creates lazily initiated value when lazy initialization throws exception.

It supports the same interface as System.Lazy<T>.

var counter = 0;
var lazy = new SyncLazy<int>(() => ++counter);

var value1 = lazy.Value;
Assert.AreEqual(1, value1);

var value2 = lazy.Value;
Assert.AreEqual(1, value2);

It also supports clearing of lazily initiated value.

var counter = 0;
var lazy = new SyncLazy<int>(() => ++counter);

var value1 = lazy.Value;
Assert.AreEqual(1, value1);

lazy.ClearValue();

var value2 = lazy.Value;
Assert.AreEqual(2, value2);

It does not cache lazy initialization exceptions.

string returnValue = null;
var lazy = new SyncLazy<string>(() => returnValue ?? throw new InvalidOperationException("Error"));

try
{
    var unused = lazy.Value;

    Assert.Fail("Exception is not thrown");
}
catch (InvalidOperationException ex) when (ex.Message == "Error")
{
}

returnValue = "Some value";

var value = lazy.Value;
Assert.AreEqual(returnValue, value);

AsyncLazy

AsyncLazy is limited async implementation of System.Lazy<T> with System.Threading.Tasks.Task<TResult> re-initialization when System.Threading.Tasks.Task<TResult> is not succefully completed.

It supports basic functionality of System.Lazy<T>.

var counter = 0;
async Task<int> ValueFactory() => await Task.Run(() => ++counter);

var lazy = new AsyncLazy<int>(ValueFactory);

var value1 = await lazy.GetValueAsync();
Assert.AreEqual(1, value1);

var value2 = await lazy.GetValueAsync();
Assert.AreEqual(1, value2);

It also supports clearing of lazily initiated value.

var counter = 0;
async Task<int> ValueFactory() => await Task.Run(() => ++counter);

var lazy = new AsyncLazy<int>(ValueFactory);

var value1 = await lazy.GetValueAsync();
Assert.AreEqual(1, value1);

lazy.ClearValue();

var value2 = await lazy.GetValueAsync();
Assert.AreEqual(2, value2);