在clang中使用别名模板时，是否有办法缩短模板化的类名?

Is there a way to shorten templated class names when using alias templates in clang?

本文关键字：是否 clang 别名      更新时间：2023-10-16

这是前面一个问题的后续问题。基本上，下面的程序

#include <memory>
// Create a class parameterized on a template
template <template <typename> class XX>
struct Foo{};
// Some template with a long name
template <typename T>
struct ReallyLongFileNameThatIHateToType {
};
// Alias to shorten name
template <typename T>
using Bar = ReallyLongFileNameThatIHateToType <T>;
int main() {
    std::unique_ptr<Foo<ReallyLongFileNameThatIHateToType>> foo =
        std::make_unique<Foo<Bar>>();
}

在GCC下可以很好地工作，而不是clang

g++ -std=c++14 test04.cpp -o test04
clang++ -std=c++14 test04.cpp -o test04
test04.cpp:20:61: error: no viable conversion from 'unique_ptr<Foo<template
      Bar>>' to
      'unique_ptr<Foo<template ReallyLongFileNameThatIHateToType>>'
    std::unique_ptr<Foo<ReallyLongFileNameThatIHateToType>> foo =
                                                            ^
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4/bits/unique_ptr.h:200:17: note: 
      candidate constructor not viable: no known conversion from 'typename
      _MakeUniq<Foo<Bar> >::__single_object' (aka 'unique_ptr<Foo<Bar> >') to
      'nullptr_t' for 1st argument
      constexpr unique_ptr(nullptr_t) noexcept : unique_ptr() { }
                ^
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4/bits/unique_ptr.h:205:7: note: 
      candidate constructor not viable: no known conversion from 'typename
      _MakeUniq<Foo<Bar> >::__single_object' (aka 'unique_ptr<Foo<Bar> >') to
      'std::unique_ptr<Foo<ReallyLongFileNameThatIHateToType>,
      std::default_delete<Foo<ReallyLongFileNameThatIHateToType> > > &&' for 1st
      argument
      unique_ptr(unique_ptr&& __u) noexcept
      ^
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4/bits/unique_ptr.h:356:7: note: 
      candidate constructor not viable: no known conversion from 'typename
      _MakeUniq<Foo<Bar> >::__single_object' (aka 'unique_ptr<Foo<Bar> >') to
      'const std::unique_ptr<Foo<ReallyLongFileNameThatIHateToType>,
      std::default_delete<Foo<ReallyLongFileNameThatIHateToType> > > &' for 1st
      argument
      unique_ptr(const unique_ptr&) = delete;
      ^
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4/type_traits:1957:41: note: 
      candidate template ignored: disabled by 'enable_if' [with _Up = Foo<Bar>,
      _Ep = std::default_delete<Foo<Bar> >]
    using _Require = typename enable_if<__and_<_Cond...>::value>::type;
                                        ^
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4/bits/unique_ptr.h:228:2: note: 
      candidate template ignored: could not match 'auto_ptr' against
      'unique_ptr'
        unique_ptr(auto_ptr<_Up>&& __u) noexcept;
        ^
1 error generated.
Makefile:2: recipe for target 'all' failed
make: *** [all] Error 1

正如链接消息中指出的，这是CWG第1244期。不管怎样，有没有其他方法可以缩短clang的名字?通常，我已经在模板类上参数化了代码，但我不想一遍又一遍地键入完整的参数名。当使用gcc时，我只是创建别名模板，然后就结束了。显然，对于clang来说，这不起作用，那么是否有不同的机制来实现相同的效果呢?

作为一种解决方法，你可以让它以其他方式工作，通过将模板模板模板参数传递给一些帮助结构体来设置它与你的模板模板参数，例如(在clang++， c++14中工作):

#include <memory>
// Create a class parameterized on a template
template <template <typename> class XX>
struct Foo{};
// Some template with a long name
template <typename T>
struct ReallyLongFileNameThatIHateToType {
};
template <template <template <class> class> class FF>
struct Bar {
  using type = FF<ReallyLongFileNameThatIHateToType>;
};
template <template <template <class> class> class FF>
using Bar_t = typename Bar<FF>::type;

int main() {
    std::unique_ptr<Foo<ReallyLongFileNameThatIHateToType>> foo =
        std::make_unique<Bar_t<Foo>>();
}
相关文章：