/// <summary>
/// Gets an option either specific to the <paramref name="serviceType"/>, or a global option (if <see cref="Options.EnableGlobalOptions"/> is
/// enabled), of the type <typeparamref name="TOption"/>
/// from the <paramref name="targets"/> target container, returning the <paramref name="default"/> if the option has not been explicitly set.
/// </summary>
/// <typeparam name="TOption">The type of option to retrieve</typeparam>
/// <param name="targets">Required. The target container from which the option is to be read.</param>
/// <param name="serviceType">A type for which the option is to be retrieved. Note that the default behaviour is to search for
/// an option which is specific to this service, and then to search for more generally-defined options. See the remarks section for more.</param>
/// <param name="default">The default value to return if the option has not been set.</param>
/// <returns>An option value which was either previously set, or the <paramref name="default"/> if not</returns>
/// <remarks>Options are frequently used to control how a Rezolver container interprets registrations. Take, for example, the
/// <see cref="Options.AllowMultiple"/> option - which is used to control whether a target container accepts multiple registrations
/// for a given type.
///
/// When defined globally (i.e. without a service type) it determines whether multiple registrations can be performed for all types. However,
/// it can also be defined on a per-service basis - so, for example, if you want to restrict an application only to register one target for a
/// particular service - e.g. <c>IMyApplication</c> - then you can set the <see cref="AllowMultiple"/> option to <c>false</c> specifically against
/// that type, and multiple registrations will result in a runtime error.
///
/// When searching for service-specific options, generics are automatically processed in descending order of specificity - i.e. <c>IFoo<Bar></c>
/// is more specific than <c>IFoo<></c> - so you can set options for a specific closed generic, or its open generic.
///
/// **Global Fallback**
///
/// In the absence of a service-specific option, a globally-defined option will instead be used if the <see cref="EnableGlobalOptions"/> option
/// is set to <c>true</c> for the <paramref name="targets"/> target container. By default, this is enabled.</remarks>
public static TOption GetOption <TOption>(this ITargetContainer targets, Type serviceType, TOption @default = default)
where TOption : class
{
if (targets == null)
{
throw new ArgumentNullException(nameof(targets));
}
if (serviceType == null)
{
throw new ArgumentNullException(nameof(serviceType));
}
bool useGlobalFallback = GetOption(targets, EnableGlobalOptions.Default);
var optionContainer = (IOptionContainer <TOption>)targets.FetchDirect(typeof(IOptionContainer <,>)
.MakeGenericType(serviceType, typeof(TOption)));
// currently internal-only option container which allows us to set options
// that take effect only for generic types (closed/open classes, structs or interfaces)
if (optionContainer == null && serviceType.IsGenericType)
{
optionContainer = targets.FetchDirect <IAnyGenericOptionContainer <TOption> >();
}
if (optionContainer == null && useGlobalFallback)
{
optionContainer = targets.FetchDirect <IOptionContainer <TOption> >();
}
return(optionContainer?.Option ?? @default);
}
/// <summary>
/// Gets a globally-defined option of the type <typeparamref name="TOption"/> from the <paramref name="targets"/> target container,
/// returning the <paramref name="default"/> if the option has not been explicitly set.
/// </summary>
/// <typeparam name="TOption">The type of option to retrieve</typeparam>
/// <param name="targets">Required. The target container from which the option is to be read.</param>
/// <param name="default">The default value to return if the option has not been set.</param>
/// <returns>An option value which was either previously set, or the <paramref name="default"/> if not</returns>
public static TOption GetOption <TOption>(this ITargetContainer targets, TOption @default = default)
where TOption : class
{
if (targets == null)
{
throw new ArgumentNullException(nameof(targets));
}
var optionContainer = targets.FetchDirect <IOptionContainer <TOption> >();
return(optionContainer?.Option ?? @default);
}
internal static TObj FetchDirect <TObj>(this ITargetContainer targets)
{
return((TObj)targets.FetchDirect(typeof(TObj)));
}