模板参数推导失败,并带有默认模板参数 [英] Template argument deduction failed with default template parameter
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问题描述
#include <cstdint>
#include <iostream>
class MyBar {
public:
void print() {
std::cout << __PRETTY_FUNCTION__ << std::endl;
}
};
template <class Bar = MyBar>
class Foo{
public:
Foo(const char* name, const uint32_t i) {
Bar b;
b.print();
}
};
int main(int argc, char** argv) {
auto pFoo1 = new Foo("abc", 3);
}
编译器给了我:
template_ctor.cpp: In function ‘int main(int, char**)’:
template_ctor.cpp:21:31: error: class template argument deduction failed:
auto pFoo1 = new Foo("abc", 3);
^
template_ctor.cpp:21:31: error: no matching function for call to ‘Foo()’
template_ctor.cpp:14:2: note: candidate: template<class Bar> Foo(const char*, uint32_t)-> Foo<Bar>
Foo(const char* name, const uint32_t i) {
^~~
template_ctor.cpp:14:2: note: template argument deduction/substitution failed:
template_ctor.cpp:21:31: note: candidate expects 2 arguments, 0 provided
auto pFoo1 = new Foo("abc", 3);
我放<>
在新Foo
之后,它将进行编译。
As soon as I put <>
after new Foo
, it compiles.
起初,我以为<> ;
是强制性的,以提示编译器使用默认模板参数,但随后我注意到,如果我删除 const char * name
,然后我不这样做't pass in abc
,它也可以编译。
At first, I thought <>
is mandatory to hint the compiler to use the default template parameter, but then I noticed that if I drop const char* name
and then I don't pass in "abc"
, then it also compiles.
现在,我很困惑。
推荐答案
这应该可以编译,并且基本上是 gcc错误85883 。此问题已在固定在树干上:
This should compile, and is basically gcc bug 85883. This has been fixed on trunk:
struct MyBar;
template <class Bar = MyBar>
class Foo{
public:
Foo(const char* name, int i);
};
auto pFoo1 = new Foo("abc", 3);
该示例在gcc 8.2上失败,但在9上编译。
The example fails on gcc 8.2, but compiles on 9.
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