如何访问类型别名中的模板模板参数？

时间：2015-05-25 17:12:09

标签： c++11 template-templates type-alias

是否可以在类型别名中使用模板模板参数？例如，是否可以编写类似于此的类型别名：

#include "tuple"

template<
    template<class... Types> class Container,
    class... Types
> using another_tuple = std::tuple<Types...>;

another_tuple<std::tuple<int>> t;

，当给出例如std :: tuple，将其类型用于其他东西？ GCC和Clang都提到错误中的类模板，如何避免需要类模板？如果我将所有...的GCC错误更改删除为：

error: wrong number of template arguments (1, should be 2)
another_tuple<std::tuple<int>> t;
                            ^

我不明白。容器本身并不一定是模板，但我无法弄清楚如何在其位置使用std :: tuple。

根据n.m.s回答更新，格式正确为：

another_tuple<std::tuple, int> t;

，即使类型在容器中也是如此：

using types = std::tuple<int, char>;
another_tuple<std::tuple, types> t;

它有一些冗余代码，但应该足够好。

1 个答案:

答案 0 :(得分：0)

   Warning: $HADOOP_HOME is deprecated.

15/05/27 11:46:35 INFO zookeeper.RecoverableZooKeeper: The identifier of this process is 6608@master
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:zookeeper.version=3.4.6-1569965, built on 02/20/2014 09:09 GMT
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:host.name=master
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:java.version=1.7.0_79
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:java.vendor=Oracle Corporation
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:java.home=/usr/lib/jvm/java-7-openjdk-amd64/jre
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:java.class.path=/usr/local/hadoop/libexec/../conf:/usr/lib/jvm/java-7-openjdk-amd64/lib/tools.jar:/usr/local/hadoop/libexec/..:/usr/local/hadoop/libexec/../hadoop-core-1.2.1.jar:/usr/local/hadoop/libexec/../lib/asm-3.2.jar:/usr/local/hadoop/libexec/../lib/aspectjrt-1.6.11.jar:/usr/local/hadoop/libexec/../lib/aspectjtools-1.6.11.jar:/usr/local/hadoop/libexec/../lib/commons-beanutils-1.7.0.jar:/usr/local/hadoop/libexec/../lib/commons-beanutils-core-1.8.0.jar:/usr/local/hadoop/libexec/../lib/commons-cli-1.2.jar:/usr/local/hadoop/libexec/../lib/commons-codec-1.4.jar:/usr/local/hadoop/libexec/../lib/commons-collections-3.2.1.jar:/usr/local/hadoop/libexec/../lib/commons-configuration-1.6.jar:/usr/local/hadoop/libexec/../lib/commons-daemon-1.0.1.jar:/usr/local/hadoop/libexec/../lib/commons-digester-1.8.jar:/usr/local/hadoop/libexec/../lib/commons-el-1.0.jar:/usr/local/hadoop/libexec/../lib/commons-httpclient-3.0.1.jar:/usr/local/hadoop/libexec/../lib/commons-io-2.1.jar:/usr/local/hadoop/libexec/../lib/commons-lang-2.4.jar:/usr/local/hadoop/libexec/../lib/commons-logging-1.1.1.jar:/usr/local/hadoop/libexec/../lib/commons-logging-api-1.0.4.jar:/usr/local/hadoop/libexec/../lib/commons-math-2.1.jar:/usr/local/hadoop/libexec/../lib/commons-net-3.1.jar:/usr/local/hadoop/libexec/../lib/core-3.1.1.jar:/usr/local/hadoop/libexec/../lib/guava-18.0.jar:/usr/local/hadoop/libexec/../lib/hadoop-capacity-scheduler-1.2.1.jar:/usr/local/hadoop/libexec/../lib/hadoop-fairscheduler-1.2.1.jar:/usr/local/hadoop/libexec/../lib/hadoop-thriftfs-1.2.1.jar:/usr/local/hadoop/libexec/../lib/hbase-0.94.24.jar:/usr/local/hadoop/libexec/../lib/hsqldb-1.8.0.10.jar:/usr/local/hadoop/libexec/../lib/jackson-core-asl-1.8.8.jar:/usr/local/hadoop/libexec/../lib/jackson-mapper-asl-1.8.8.jar:/usr/local/hadoop/libexec/../lib/jasper-compiler-5.5.12.jar:/usr/local/hadoop/libexec/../lib/jasper-runtime-5.5.12.jar:/usr/local/hadoop/libexec/../lib/jdeb-0.8.jar:/usr/local/hadoop/libexec/../lib/jersey-core-1.8.jar:/usr/local/hadoop/libexec/../lib/jersey-json-1.8.jar:/usr/local/hadoop/libexec/../lib/jersey-server-1.8.jar:/usr/local/hadoop/libexec/../lib/jets3t-0.6.1.jar:/usr/local/hadoop/libexec/../lib/jetty-6.1.26.jar:/usr/local/hadoop/libexec/../lib/jetty-util-6.1.26.jar:/usr/local/hadoop/libexec/../lib/jsch-0.1.42.jar:/usr/local/hadoop/libexec/../lib/junit-4.5.jar:/usr/local/hadoop/libexec/../lib/kfs-0.2.2.jar:/usr/local/hadoop/libexec/../lib/log4j-1.2.15.jar:/usr/local/hadoop/libexec/../lib/mockito-all-1.8.5.jar:/usr/local/hadoop/libexec/../lib/oro-2.0.8.jar:/usr/local/hadoop/libexec/../lib/protobuf-java-2.4.0a.jar:/usr/local/hadoop/libexec/../lib/servlet-api-2.5-20081211.jar:/usr/local/hadoop/libexec/../lib/slf4j-api-1.4.3.jar:/usr/local/hadoop/libexec/../lib/slf4j-log4j12-1.4.3.jar:/usr/local/hadoop/libexec/../lib/xmlenc-0.52.jar:/usr/local/hadoop/libexec/../lib/zookeeper-3.4.6.jar:/usr/local/hadoop/libexec/../lib/jsp-2.1/jsp-2.1.jar:/usr/local/hadoop/libexec/../lib/jsp-2.1/jsp-api-2.1.jar
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:java.library.path=/usr/local/hadoop/libexec/../lib/native/Linux-amd64-64
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:java.io.tmpdir=/tmp
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:java.compiler=<NA>
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:os.name=Linux
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:os.arch=amd64
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:os.version=3.5.0-60-generic
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:user.name=hduser
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:user.home=/home/hduser
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Client environment:user.dir=/usr/local/hadoop
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Initiating client connection, connectString=zks2:2181,zks1:2181,zks3:2181 sessionTimeout=180000 watcher=hconnection
15/05/27 11:46:35 INFO zookeeper.ClientCnxn: Opening socket connection to server zks3/192.168.4.66:2181. Will not attempt to authenticate using SASL (unknown error)
15/05/27 11:46:35 INFO zookeeper.ClientCnxn: Socket connection established to zks3/192.168.4.66:2181, initiating session
15/05/27 11:46:35 INFO zookeeper.ClientCnxn: Session establishment complete on server zks3/192.168.4.66:2181, sessionid = 0x34d94005a530003, negotiated timeout = 60000
15/05/27 11:46:35 INFO client.HConnectionManager$HConnectionImplementation: Closed zookeeper sessionid=0x34d94005a530003
15/05/27 11:46:35 INFO zookeeper.ZooKeeper: Session: 0x34d94005a530003 closed
15/05/27 11:46:35 INFO zookeeper.ClientCnxn: EventThread shut down
connected to hbase
Before
After
15/05/27 11:46:38 INFO zookeeper.RecoverableZooKeeper: The identifier of this process is 6608@master
15/05/27 11:46:38 INFO zookeeper.ZooKeeper: Initiating client connection, connectString=zks2:2181,zks1:2181,zks3:2181 sessionTimeout=180000 watcher=hconnection
15/05/27 11:46:38 INFO zookeeper.ClientCnxn: Opening socket connection to server zks2/192.168.4.61:2181. Will not attempt to authenticate using SASL (unknown error)
15/05/27 11:46:38 INFO zookeeper.ClientCnxn: Socket connection established to zks2/192.168.4.61:2181, initiating session
15/05/27 11:46:38 INFO zookeeper.ClientCnxn: Session establishment complete on server zks2/192.168.4.61:2181, sessionid = 0x24d93f965730002, negotiated timeout = 60000

如果你希望列表在前面用int扩展，在末尾加倍：

template<class T>struct tag{using type=T;};
template<class Tag>using type_t=typename Tag::type;
template<class...>struct types{using type=types;};

template<template<class...>class Z, class types>
struct apply_types;
template<template<class...>class Z, class types>
using apply_types_t=type_t<apply_types<Z,types>>;
template<template<class...>class Z, class...Ts>
struct apply_types<Z,types<Ts...>>:tag<Z<Ts...>> {};

template<template<class...>class M, class types>
struct map;
template<template<class...>class M, class types>
using map_t=type_t<map<M,types>>;
template<template<class...>class M, class...Ts>
struct map<M,types<Ts...>>:types<M<Ts>...>{};

template<class...lists>
struct concat:types<>{};
template<class...lists>
using concat_t=type_t<concat<lists...>>;
template<class...lhs, class...rhs>
struct concat<types<lhs...>,types<rhs...>>:
  types<lhs...,rhs...>
{};
template<class types>
struct concat<types>:
  types
{};
template<class types, class...more_types>
struct concat<types, more_types...>:
  concat<types, concat_t<more_types...>>
{};

template<class A, template<class...>class C, class T, class F>
struct condition:std::conditional<C<A>{}, T, F>{};

template<template<class...>class Z, class... T>
struct bind_1st_n {
  template<class...Ts>
  using apply=Z<T..., Ts...>;
};

template<class Tok, class list, class A>
struct replace_helper:
  condition<A, bind_1st_n<std::is_same, Tok>::template apply, list, types<A>>
{};

template<class list, class if_this, class then_these>
struct replace:
  concat<
    map_t<
      bind_1st_n<replace_helper,if_this, then_these>::template apply,
      list
    >
  >
{};

struct placeholder {};

template<class T> struct get_args;
template<class T> using get_args_t=type_t<get_args<T>>;
template<template<class...>class Z, class...Ts>
struct get_args<Z<Ts...>>:types<Ts...> {};

template<template<class...>class Z, class types>
struct apply;
template<template<class...>class Z, class types>
using apply_t=type_t<apply<Z,types>>;


template< class Container >
using another_tuple = apply_t< std::tuple, get_args_t<Container> >;

构建要应用的列表，然后分两步应用它。

此代码均未编译。

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