c++ - 如何有效地将 if 和 else 用于过滤结构？

Question

为了解析从 JavaScript 获取的函数参数，我需要执行大量检查。例如，一个函数可能需要一个对象作为参数，在 JavaScript 中看起来像这样。

{
    Fullscreen: [ 'bool',     false         ],
    Size:       [ 'Vector2u', 800, 600      ],
    Title:      [ 'string',   'Hello World' ],
    // more properties...
}

在 C++ 中，我通过遍历所有键并检查它们来解析它。如果其中一项检查失败，则应打印错误消息并跳过此键值对。这就是我目前的实现方式。我希望您不会因某些特定于引擎的调用而分心。

ModuleSettings *module = (ModuleSettings*)HelperScript::Unwrap(args.Data());

if(args.Length() < 1 || !args[0]->IsObject())
    return v8::Undefined();
v8::Handle<v8::Object> object = args[0]->ToObject();

auto stg = module->Global->Get<Settings>("settings");

v8::Handle<v8::Array> keys = object->GetPropertyNames();
for(unsigned int i = 0; i < keys->Length(); ++i)
{
    string key = *v8::String::Utf8Value(keys->Get(i));
    if(!object->Get(v8::String::New(key.c_str()))->IsArray())
    {
        HelperDebug::Fail("script", "could not parse (" + key + ") setting");
        continue;
    }
    v8::Handle<v8::Array> values = v8::Handle<v8::Array>::Cast(object->Get(v8::String::New(key.c_str())));

    if(!values->Has(0) || !values->Get(0)->IsString())
    {
        HelperDebug::Fail("script", "could not parse (" + key + ") setting");
        continue;
    }
    string type = *v8::String::Utf8Value(values->Get(0));

    if(type == "bool")
    {
        if(!values->Has(1) || !values->Get(1)->IsBoolean())
        {
            HelperDebug::Fail("script", "could not parse (" + key + ") setting");
            continue;
        }
        stg->Set<bool>(key, values->Get(1)->BooleanValue());
    }
    else if(type == "Vector2u")
    {
        if(!values->Has(1) || !values->Has(2) || !values->Get(1)->IsUint32(), !values->Get(2)->IsUint32())
        {
            HelperDebug::Fail("script", "could not parse (" + key + ") setting");
            continue;
        }
        stg->Set<Vector2u>(key, Vector2u(values->Get(1)->Uint32Value(), values->Get(2)->Uint32Value()));
    }
    else if(type == "string")
    {
        if(!values->Has(1) || !values->Get(1)->IsString())
        {
            HelperDebug::Fail("script", "could not parse (" + key + ") setting");
            continue;
        }
        stg->Set<string>(key, *v8::String::Utf8Value(values->Get(1)));
    }
}

如您所见，我定义了在每个过滤器检查失败时发生的时间。

HelperDebug::Fail("script", "could not parse (" + key + ") setting");
continue;

我只想写一次，但我只能想出一种使用 goto 的方法，我想避免这种方法。是否有更好的选择来重构 if else 结构？

Answer 1

我想我会从一组小类开始为每种类型执行验证步骤:

auto v_string = [](v8::Handle<v8::Array> const &v) { 
    return v->Has(1) && v->Get(1)->IsString(); 
}

auto v_Vector2u = [](v8::Handle<v8::Array> const &v) { 
    return v->Has(1) && v->Has(2) && 
           v->Get(1)->IsUint32() && v->Get(2)->IsUint32(); 
}
// ...

然后我会创建一个从类型名称到该类型验证器的映射:

std::map<std::string, decltyp(v_string)> verifiers;

verifiers["string"] = v_string;
verifiers["Vector2u"] = v_Vector2u;
// ...

然后为了验证一个类型，你会使用这样的东西:

// find the verifier for this type:
auto verifier = verifiers.find(type);

// If we can't find a verifier, reject the data:
if (verifier == verifiers.end())
    HelperDebug::Fail("script", "unknown type: " + type);

// found the verifier -- verify the data:
if (!verifier->second(values))
    HelperDebug::Fail("script", "could not parse (" + key + ") setting");