/// <summary>
/// Initializes a new instance of the <see cref="SmartList{T}"/> class.
/// </summary>
/// <param name="enumerable">The enumerable.</param>
public SmartList(IEnumerable <T> enumerable)
{
#region Contract
if (enumerable == null)
{
throw new ArgumentNullException(nameof(enumerable));
}
#endregion
this.innerList = enumerable as IReadOnlyList <T>;
if (this.innerList != null)
{
// We have converted the enumerable to a list.
// We're done and can simply enumerate the list.
this.count = this.innerList.Count;
this.enumerator = null;
}
else
{
// Maybe the enumerable is actually a collection, list, or set,
// so we can determine the number of elements cheaply.
this.count = Enumerables.TryGetCount(enumerable);
this.innerList = this.count != null ? new List <T>((int)this.count) : new List <T>();
this.enumerator = enumerable.GetEnumerator();
}
}
public void ShouldReturnNull_WhenEnumerableIsNotACollection()
{
// Arrange
var enumerable = new [] { "a", "b", "c" }.Select(s => s);
// Act
int?result = Enumerables.TryGetCount(enumerable);
// Assert
Assert.Null(result);
}
public void ShouldReturnTheCount_WhenEnumerableIsAnICollection()
{
// Arrange
var collection = new ArrayList {
"a", "b", "c"
};
// Act
int?result = Enumerables.TryGetCount(collection);
// Assert
Assert.Equal(3, result);
}
/// <summary>
/// Compares the number of elements in the two collections, if possible.
/// </summary>
/// <param name="x">The first collection.</param>
/// <param name="y">The second collection.</param>
/// <returns><see langword="true"/> when the collections have a mismatching
/// number of elements; otherwise, <see langword="false"/>.</returns>
private static bool HaveMismatchingCounts([NoEnumeration] IEnumerable <T> x, [NoEnumeration] IEnumerable <T> y)
{
#region Contract
Debug.Assert(x != null);
Debug.Assert(y != null);
#endregion
var xcount = Enumerables.TryGetCount(x);
var ycount = Enumerables.TryGetCount(y);
return(xcount != null &&
ycount != null &&
xcount != ycount);
}
public void ShouldThrowArgumentNullException_WhenEnumerableIsNull()
{
// Arrange
IReadOnlyCollection <String> enumerable = null;
// Act
var exception = Record.Exception(() =>
{
Enumerables.TryGetCount(enumerable);
});
// Assert
Assert.IsType <ArgumentNullException>(exception);
}