approach to meta programming Author: Andreas Rumpf A new approach to metaprogramming Copyright © 2013 Andreas Rumpf Talk structure 1.What is Nimrod? 2.Implementation aspects 3."Hello World" 4.Meta programming "Hello World" via term rewriting macros 6.Hoisting via term rewriting macros 7.Summary of Nimrod's meta programming features Talk structure Copyright © 2013 Andreas Rumpf What is Nimrod? What is Nimrod cast[int](gch.stackBottom) • with a clean syntax iterator from1to2(): int = yield 1; yield 2 • and strong meta programming capabilities. template `!=`(x, y: expr): expr = not (x == y) What is Nimrod? Copyright

1 / 58Template Metaprogramming (TMP) Template Metaprogramming (TMP) template using meta_fun = this_talk; 2 / 58❓static_assert(Template::Metaprogramming::is_hard); // ✔ 3 / 58❓s Value-based TMP ( - Value-based TMP ( *, *, *)*) - - (Circle-lang meta model*) (Circle-lang meta model*) - - (comptime) (comptime) - ... - ... * - this_talk * - this_talk C++ template inline constexpr auto meta = type::id; static_assert(meta == meta); static_assert(meta != meta); static_assert(typeid(meta) == typeid(meta)); 16 / 58Value-based

implementation(s)! 2425We have a reflection operator! using namespace std::meta; auto magic_reflection_method(info obj) { .. do something with “meta” info .. } // ^Lift^ MyType to reflection land auto result = namespace ... 26We have a reflection operator! using namespace std::meta; auto magic_reflection_method(info obj) { .. do something with “meta” info .. } // ^^Lift^^ MyType to reflection land auto result 27We have a std::meta::info! using namespace std::meta; // std::meta::info with std::meta // associated namespace auto magic_reflection_method(info obj) .. do something with “meta” info .. } auto

John R. Bandela, MD Beyond struct: Meta- programming a struct Replacement in C++20Disclaimer This is not an official Google library These opinions are my ownStruct struct person { int id = 1; std::string wrappers in C++Let’s Go Beyond Struct u C++20 u No MacrosDefining and accessing members using Person = meta_struct< // member<"id", int>, // member<"name", std::string> // >; Person p; get<"id">(p) - 1>;Meta Struct template struct member { constexpr static auto tag() { return Tag; } using element_type = T; T value; }; template struct meta_struct

....................................................................................... 28 6.4 Meta 和数据迁移 ........................................................................................... ......... 30 6.4.2 方案 A：通过 MMA Agent 迁移 Meta 和数据 ................................................................ 32 6.4.3 方案 B：使用 Dataworks 服务迁移 Meta 和数据 ....................................... .................... 45 7.1.3 运行 meta-carrier 收集 meta 信息 ................................................................................... 46 7.1.4 修改 meta-carrier 的输出，调整 hive 与 odps 的映射 .....

Person(Model): name = CharField() birthday = DateField() is_relative = BooleanField() class Meta: database = db # This model uses the "people.db" database. Note Note that we named our model ForeignKeyField(Person, related_name='pets') name = CharField() animal_type = CharField() class Meta: database = db # this model uses the "people.db" database Now that we have our models, let’s then, any subclasses will automatically # use the correct storage. class BaseModel(Model): class Meta: database = database # the user model specifies its fields (or columns) declaratively, like

class Person(Model): name = CharField() birthday = DateField() is_relative = BooleanField() class Meta: database = db # This model uses the "people.db" database. Note: Note that we named our model Person = ForeignKeyField(Person, related_name='pets') name = CharField() animal_type = CharField() class Meta: database = db # this model uses the "people.db" database Now that we have our models, let’s connect then, any subclasses will automatically # use the correct storage. class BaseModel(Model): class Meta: database = database # the user model specifies its fields (or columns) declaratively, like django

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callback for parsing the response • --meta or -m: additional request meta that will be passed to the callback request. This must be a valid json string. Example: –meta=’{“foo” : “bar”}’ • --pipelines: process itemprop="author">Ellie, ... <meta itemprop="datePublished" content="2011-04-01">April 1, 2011 ...