c# - 在 C# 的内部类中实现内部接口(interface)

Question

为什么不允许在内部类中实现内部接口(interface)？这种限制是否有特定原因，或者仅仅是语言设计决定？

internal interface IDefinition
{
    string GetValueAsString(string property);
}

internal sealed class DefinitionArray : IDefinition
{
    internal string GetValueAsString(string property)
    {
        return m_definitionRows
            .Select(o => o.GetValueAsString(property))
            .FirstOrDefault();
    }
}

Answer 1

C# 6.0 语言规范的§3.5.6 指出:

Interface members implicitly have public declared accessibility. No access modifiers are allowed on interface member declarations.

所以你“理论上”拥有的是

internal interface IDefinition
{
    public string GetValueAsString(string property);
}

但这不是问题，因为(§3.5.2):

The accessibility domain of a nested member M declared in a type T within a program P is defined as follows (noting that M itself may possibly be a type):

• If the declared accessibility of M is public, the accessibility domain of M is the accessibility domain of T.

因此，成员的可访问性与声明为 internal 时等效。