在聚合初始化期间无法访问继承的结构成员

Question

struct BasePluginInfo
{
    bool bHasGui, bIsSynth;
    char cType;
    std::string sCategory, sSdkVersion, sVendor, sVersion;
};

struct PluginClassInfo
{
    std::string sName, sUid;
    std::vector<std::string> vsParamNames;
};

struct ShellPluginInfo : BasePluginInfo
{
    std::vector<PluginClassInfo> vciClasses;
};

When I do

ShellPluginInfo
{
    .bHasGui = true
};

The compiler complains that ShellPluginInfo has no field 'bHasGui' .

However this works:

ShellPluginInfo info;
info.bHasGui = true;

SO complains I have too much code, so these are a few words to fill it up.

Answer 1

When aggregate initializing something with base classes, the base class acts like a member of the class, similar to if you had:

struct ShellPluginInfo {
    BasePluginInfo __base_class_subobject;
    std::vector<PluginClassInfo> vciClasses;
};

As such, the first clause in the initializer list will try to initialize it, and you have to write:

ShellPluginInfo{  // This initializer list initializes a ShellPluginInfo
    { .bHasGui = true; }  // This initializer list initializes a BasePluginInfo
}

---

However, since this is not a designated initializer, you cannot use designated initializers for the rest of the members of the derived class. For example:

ShellPluginInfo{
    {  // (note: doesn't have a designator)
        .bHasGui = true,
        .cType = 'a'  // OK
    },
    .vciClasses = {}  // ERROR: Can't mix designated and non-designated initializers

}

This proposal attempts to remedy that: https://wg21.link/p2287r1 , making your original attempt valid. It has not been accepted yet though, but you may see it in C++23.