c# - 通用接口(interface)约束

Question

我正在尝试减少以下代码:

public interface IQuestion<TSite, TStyling, TRelation> : IShallowPost
    where TSite : INetworkSite<TStyling, TRelation>
    where TStyling : INetworkSiteStyling
    where TRelation : INetworkSiteRelation
{

对于这样的事情:

public interface IQuestion<TSite> : IShallowPost
    where TSite : INetworkSite<TStyling, TRelation>
    where TStyling : INetworkSiteStyling
    where TRelation : INetworkSiteRelation
{

我怎样才能做到这一点？

自从有了这样的事情:

internal sealed class Question : IQuestion<NetworkSite, NetworkSiteStyling, NetworkSiteRelation>

与相比，对我来说没有什么意义

internal sealed class Question : IQuestion<NetworkSite>

更新@Jared

当然，就是这样。

/// <summary>
/// Represents a question on one of the Stack Exchange sites.
/// <para>https://api.stackexchange.com/docs/types/question</para>
/// </summary>
/// <typeparam name="TSite">The concrete type of <see cref="INetworkSite{TStyling,TRelation}"/>.</typeparam>
/// /// <typeparam name="TStyling">The concrete type of <see cref="INetworkSiteStyling"/>.</typeparam>
/// <typeparam name="TRelation">The concrete type of <see cref="INetworkSiteRelation"/>.</typeparam>
/// <typeparam name="TMigrationInfo">The concrete type of <see cref="IMigrationInfo{TSite,TStyling,TRelation}"/>.</typeparam>
/// <typeparam name="TShallowUser">The concrete type of <see cref="IShallowUser"/>.</typeparam>
/// <typeparam name="TComment">The concrete type of <see cref="IComment{TShallowUser}"/>.</typeparam>
/// <typeparam name="TAnswer">The concrete type of <see cref="IAnswer{TShallowUser,TComment}"/>.</typeparam>
public interface IQuestion<TShallowUser, TComment, TMigrationInfo, TSite, TStyling, TRelation, TAnswer> : IShallowPost<TShallowUser, TComment>
    where TShallowUser : IShallowUser
    where TComment : IComment<TShallowUser>
    where TSite : INetworkSite<TStyling, TRelation>
    where TStyling : INetworkSiteStyling
    where TRelation : INetworkSiteRelation
    where TMigrationInfo : IMigrationInfo<TSite, TStyling, TRelation>
    where TAnswer : IAnswer<TShallowUser, TComment>
{
    /// <summary>
    /// The id of this question.
    /// </summary>
    [JsonProperty("question_id")]
    long? QuestionId { get; set; }
    /// <summary>
    /// The date this question was locked.
    /// </summary>
    [JsonConverter(typeof(UnixDateTimeConverter))]
    [JsonProperty("locked_date")]
    DateTime? LockedDate { get; set; }
    /// <summary>
    /// The date this question was marked as community wiki.
    /// </summary>
    [JsonConverter(typeof(UnixDateTimeConverter))]
    [JsonProperty("community_owned_date")]
    DateTime? CommunityOwnedDate { get; set; }
    /// <summary>
    /// The amount of answers posted in response to this question.
    /// </summary>
    [JsonProperty("answer_count")]
    long? AnswerCount { get; set; }
    /// <summary>
    /// The id of the accepted answer, if any.
    /// </summary>
    [JsonProperty("accepted_answer_id")]
    long? AcceptedAnswerId { get; set; }
    /// <summary>
    /// Migration info telling where this question was migrated to.
    /// </summary>
    [JsonProperty("migrated_to")]
    TMigrationInfo MigratedTo { get; set; }
    /// <summary>
    /// Migration info telling where this question was migrated from.
    /// </summary>
    [JsonProperty("migrated_from")]
    TMigrationInfo MigratedFrom { get; set; }
    /// <summary>
    /// Date when the active bounty on this question ends.
    /// </summary>
    [JsonConverter(typeof(UnixDateTimeConverter))]
    [JsonProperty("bounty_closes_date")]
    DateTime? BountyClosesDate { get; set; }
    /// <summary>
    /// The amount of reputation spent on the bounty.
    /// </summary>
    [JsonProperty("bounty_amount ")]
    long? BountyAmount { get; set; }
    /// <summary>
    /// The date this question was closed.
    /// </summary>
    [JsonConverter(typeof(UnixDateTimeConverter))]
    [JsonProperty("closed_date")]
    DateTime? ClosedDate { get; set; }
    /// <summary>
    /// The date this question was marked as protected.
    /// </summary>
    [JsonConverter(typeof(UnixDateTimeConverter))]
    [JsonProperty("protected_date")]
    DateTime? ProtectedDate { get; set; }
    /// <summary>
    /// The title of this question.
    /// </summary>
    [JsonProperty("title")]
    string Title { get; set; }
    /// <summary>
    /// A list of tags applied on this question.
    /// </summary>
    [JsonProperty("tags")]
    IList<string> Tags { get; set; }
    /// <summary>
    /// The reason this post was closed.
    /// </summary>
    [JsonProperty("closed_reason")]
    string ClosedReason { get; set; }
    /// <summary>
    /// The amount of users who favorited this question.
    /// </summary>
    [JsonProperty("favorite_count")]
    long? FavoriteCount { get; set; }
    /// <summary>
    /// The amount of views this question had.
    /// </summary>
    [JsonProperty("view_count")]
    long? ViewCount { get; set; }
    /// <summary>
    /// A list of answers posted on this question.
    /// </summary>
    [JsonProperty("answers")]
    IList<TAnswer> Answers { get; set; }
    /// <summary>
    /// A link to the question.
    /// </summary>
    [JsonProperty("link")]
    string Link { get; set; }
    /// <summary>
    /// A boolean indicating whether this question is answered or considered unanswered.
    /// </summary>
    [JsonProperty("is_answered")]
    bool? IsAnswered { get; set; }
}

由于 Json 反序列化，我需要具体类型而不是接口(interface)，但我真的讨厌必须传递那些巨大的泛型类型列表。太丑了。

Answer 1

如果您使用 C# 4 或更高版本并将 INetworkSite 的两个类型参数声明为协变，则可以缩短该约束，这将使您的接口(interface)如下所示:

public interface IQuestion<TSite> : IShallowPost
    where TSite : INetworkSite<INetworkSiteStyling, INetworkSiteRelation>
{
    // interface members
}

public interface INetworkSite<out TStyling, out TRelation>
    // these constraints are not actually needed for the example to work,
    // but they seemed logical, so I left them in
    where TStyling : INetworkSiteStyling
    where TRelation : INetworkSiteRelation
{
    // interface members
}

但是，如果 INetworkSite 需要给定类型的任何类型的输入(方法参数、引用参数、可设置属性)，则这将不起作用，从而迫使您保持约束不变。

当然，可以仅将一个类型参数定义为协变，从而只允许将该类型参数排除在约束之外。