Enforce order of builder

builder.cc

class SystemBuilder
{
private:
    class SystemBuilderConnections
    {
    public:
        SystemBuilderConnections(SystemBuilder& parent):
            parent(parent)
        {
        }

        SystemBuilderConnections& withConnections(int y)
        {
            return *this;
        }

        void build()
        {
        }

    private:
        SystemBuilder& parent;
    };

    SystemBuilderConnections sbc;

public:
    SystemBuilder():
        sbc(*this)
    {
    }

    SystemBuilderConnections& withComponents(int x)
    {
        return sbc;
    }
};

int main()
{
    SystemBuilder builder;
    builder.withComponents(1).withConnections(2).build();
    // connect.cc:32:13: error: ‘class SystemBuilder’ has no member named ‘withConnections’
    // builder.withConnections(2).withComponents(1).build();
}