在水晶中获取有关继承链的信息

Question

只是出于好奇并了解一下 Crystal 的一般结构，我正在寻找一些反射功能，让我更好地了解继承链是如何构建的。

我在想像红宝石的超阶级、祖先或included_modules方法。

水晶语言中是否有类似的东西？

此外，有某种可以向我展示大局的图表会很有用。

Answer 1

Crystal 中的元编程是使用宏实现的。

宏是在编译时接收 AST 节点并生成粘贴到程序中的代码的方法。

Crystal 已经实现了superclass和ancestors，它们在编译时返回结果。所以你可以做到：

{{ pp MyClass.superclass }}
{{ pp MyClass.ancestors }}

为方便起见，为了检查继承，您可以编写自己的宏。考虑到学习目的，它可能看起来像这样：

class Class
def superclass
{{ @type.superclass }}
end
def ancestors
{% if @type.ancestors.size > 0 %}
{{ @type.ancestors }}
{% else %}
[] of Nil
{% end %}
end
def included_modules
{% if @type.ancestors.any? { |a| a.class.stringify.ends_with?(":Module") } %}
{{ @type.ancestors.select { |a| a.class.stringify.ends_with?(":Module") } }}
{% else %}
[] of Nil
{% end %}
end
def inheritance_chain
String.build do |chain|
cls = self
chain << cls
while !(cls = cls.superclass).nil?
chain << " > #{cls}"
end
end
end
end

然后你可以做检查：

class A
end
module B
end
require "crystal/system/random"
class C < A
include B
include Crystal::System::Random
end
C.name             # => "C"
C.superclass       # => A
C.ancestors        # => [Crystal::System::Random, B, A, Reference, Object]
C.included_modules # => [Crystal::System::Random, B]
A.included_modules # => []

如果你走得更远：

C.superclass                                                    # => A
C.superclass.try &.superclass                                   # => Reference
C.superclass.try &.superclass.try &.superclass                  # => Object
C.superclass.try &.superclass.try &.superclass.try &.superclass # => nil

现在使用inheritance_chain：

Int32.inheritance_chain                          # => "Int32 > Int > Number > Value > Object"
String.inheritance_chain                         # => "String > Reference > Object"
Float64.inheritance_chain                        # => "Float64 > Float > Number > Value > Object"
Array(Bool).inheritance_chain                    # => "Array(Bool) > Reference > Object"
Hash(Bool, Bool).inheritance_chain               # => "Hash(Bool, Bool) > Reference > Object"
Tuple(Char).inheritance_chain                    # => "Tuple(Char) > Struct > Value > Object"
NamedTuple(s: String, b: Bool).inheritance_chain # => "NamedTuple(s: String, b: Bool) > Struct > Value > Object"
Nil.inheritance_chain                            # => "Nil > Value > Object"
Regex.inheritance_chain                          # => "Regex > Reference > Object"
Symbol.inheritance_chain                         # => "Symbol > Value > Object"
Proc(Int32).inheritance_chain                    # => "Proc(Int32) > Struct > Value > Object"
Set(String).inheritance_chain                    # => "Set(String) > Struct > Value > Object"
Exception.inheritance_chain                      # => "Exception > Reference > Object"
Class.inheritance_chain                          # => "Class > Value > Object"
# union
alias UnionType = Int32 | Nil | String
UnionType.inheritance_chain                      # => "(Int32 | String | Nil) > Value > Object"
# nilable
Int32?.inheritance_chain                         # => "(Int32 | Nil) > Value > Object"
# pointer
alias Int32Ptr = Int32*
Int32Ptr.inheritance_chain                       # => "Pointer(Int32) > Struct > Value > Object"
# ...