/// <summary>
/// Registers an alias for one type to another type.
///
/// The created entry will effectively represent a second Resolve call into the container for the aliased type.
/// </summary>
/// <param name="targetContainer">The builder in which the alias is to be registered</param>
/// <param name="aliasType">The type to be registered as an alias</param>
/// <param name="originalType">The type being aliased.</param>
/// <remarks>Use this when it's important that a given target type is always served through the same compiled target, even when the consumer
/// expects it to be of a different type. A very common scenario is when you have a singleton instance of the <paramref name="originalType" />,
/// and need to serve that same instance for <paramref name="aliasType"/>. If you register the same singleton for both types, you get two
/// separate singletons for each type, whereas if you create an alias, both will be served by the same alias.
/// </remarks>
public static void RegisterAlias(this ITargetContainer targetContainer, Type aliasType, Type originalType)
{
if (targetContainer == null)
{
throw new ArgumentNullException(nameof(targetContainer));
}
if (aliasType == originalType)
{
throw new ArgumentException("The aliased type and its alias must be different", nameof(aliasType));
}
ITarget target = new ResolvedTarget(originalType);
// if there's no implicit conversion to our alias type from the aliased type, but there is
// the other way around, then we need to stick in an explicit change of type, otherwise the registration will
// fail. This does, unfortunately, give rise to the situation where we could be performing an invalid cast - but that
// will come out in the wash at runtime.
if (!aliasType.IsAssignableFrom(originalType) &&
originalType.IsAssignableFrom(aliasType))
{
target = new ChangeTypeTarget(target, aliasType);
}
targetContainer.Register(target, aliasType);
}
public void ShouldConstructChangeTypeTarget()
{
var innerTarget = CreateTestTarget();
var target = new ChangeTypeTarget(innerTarget, typeof(ValidTypeForTestTarget));
Assert.Same(innerTarget, target.InnerTarget);
}
