AngularJS orderBy日期过滤器无法使用Firebase(AngularJS orderBy date filter not working using Firebase)

 枚举的一点是您创建一个只能采用固定值的新类型 。 因为在实际使用中只有很多间隔，并且因为在这里创建新类型比使用整型常量更方便，所以对于您的间隔使用枚举是合适的。 
 
 你的和弦的故事是不同的。 你已经有了和弦的类型，所以把它们包装在另一个枚举类型中是没有用的。 另外，和弦的数量远没有限制。 我手边的和弦图表显示了22种形状，但不包括反转。 你的和弦结构远比用enum限制和弦更合适。 
 
 除了枚举之外，C还有另外两种创建“常量”的机制：预处理器定义和静态变量。 
 
 使用预处理器指令，我们可以定义一个Chord文字。 IIRC结构文字是C99的东西，以前只能有初始化文字。 
 
#define CHORD_MAJOR ((Chord){"maj", {ROOT, MAJOR_THIRD, PERFECT_FIFTH}})
 
 有了一个静态变量，你可以在头文件中声明一个对象： 
 
static const Chord chord_major = {"maj", {ROOT, MAJOR_THIRD, PERFECT_FIFTH}};
 
 请注意，C没有像::这样的名称空间运算符。 相反，你必须自己为任何可能的冲突标识符加上前缀。 C ++确实有名称空间，但这不会影响在此答案中所做的要点。 

The point of an enum is that you create a new type that can only take on a fixed set of values. It is appropriate to use an enum for your intervals because there are only so many intervals in actual use, and because creating a new type is more convenient than using integer constants here.
 
The story is different for your chords. You already have a type for your chords, so wrapping them in another enum type is not helpful. Also, the number of chords is far less finite. A chord chart I have at hand shows 22 shapes, but that does not include inversions. Your chord struct is far more appropriate than artificially limiting chords with an enum.
 
C has two other mechanisms to create “constants” other than enums: preprocessor-defines and static variables.
 
With a preprocessor directive, we can define a Chord literal. IIRC struct literals are a C99 thing, previously there could only be initializer literals.
 
#define CHORD_MAJOR ((Chord){"maj", {ROOT, MAJOR_THIRD, PERFECT_FIFTH}})
 
With a static variable, you would declare an object in a header:
 
static const Chord chord_major = {"maj", {ROOT, MAJOR_THIRD, PERFECT_FIFTH}};
 
Note that C does not have a namespace operator like ::. Instead, you have to prefix any possibly clashing identifiers yourself. C++ does have namespaces, but that doesn't affect the points made in this answer.