我有一些实现 Pareto 规则的通用代码。它看起来像是格式正确的代码。
关于 newResult.set<Criterion>( criterion() );
错误的 GCC 4.4 编译器消息表达。但我找不到问题。
完整错误日志:
trunk$ g++ -std=c++0x -o test test.cpp
t6.cpp: In member function ‘bool Pareto<Minimize<T>, Types ...>::operator()(Map&, Map&)’:
t6.cpp:24: error: expected primary-expression before ‘>’ token
t6.cpp:26: error: expected primary-expression before ‘>’ token
t6.cpp:26: error: expected primary-expression before ‘)’ token
t6.cpp:26: error: expected primary-expression before ‘>’ token
t6.cpp:26: error: expected primary-expression before ‘)’ token
t6.cpp: In member function ‘bool Pareto<Maximize<T>, Types ...>::operator()(Map&, Map&)’:
t6.cpp:43: error: expected primary-expression before ‘>’ token
t6.cpp:45: error: expected primary-expression before ‘>’ token
t6.cpp:45: error: expected primary-expression before ‘)’ token
t6.cpp:45: error: expected primary-expression before ‘>’ token
t6.cpp:45: error: expected primary-expression before ‘)’ token
完整代码 list :
// TypeMap
template < typename ... Tail >
struct Holder;
template <typename ValueType, typename Head, typename ... Tail >
struct Holder<ValueType, Head, Tail ... > :
public Holder<ValueType, Head>,
public Holder<ValueType, Tail ... >
{};
template <typename ValueType, typename Head >
struct Holder<ValueType, Head>
{
ValueType value;
};
template < typename ... Types >
struct TypeMap;
template <typename ValueType, typename ... Types >
struct TypeMap<ValueType, Types ... > :
public Holder<ValueType, Types ... >
{
template <typename T>
void set(const ValueType& value)
{
((Holder<ValueType, T>*)this)->value = value;
}
template <typename T>
ValueType get()
{
return ((Holder<ValueType, T>*)this)->value;
}
};
// Objectives
template <typename Criterion> struct Maximize : public Criterion {};
template <typename Criterion> struct Minimize : public Criterion {};
// Criteria
struct Criterion1{ double operator()(){ return 0; }};
struct Criterion2{ double operator()(){ return 0; }};
// Pareto rule
template < typename ... Types > struct Pareto;
template < typename T, typename ... Types >
struct Pareto<Minimize<T>, Types ... >
{
template< typename Map >
bool operator()(Map& oldResult, Map& newResult)
{
typedef Minimize<T> Criterion;
Criterion criterion;
// ERROR HERE !!!
newResult.set<Criterion>( criterion() );
if(newResult.get<Criterion>() >= oldResult.get<Criterion>())
return false;
Pareto<Types ... > pareto;
return pareto(oldResult, newResult);
}
};
template < typename T, typename ... Types >
struct Pareto<Maximize<T>, Types ... >
{
template< typename Map >
bool operator()(Map& oldResult, Map& newResult)
{
typedef Maximize<T> Criterion;
Criterion criterion;
// ERROR HERE !!!
newResult.set<Criterion>( criterion() );
if(newResult.get<Criterion>() <= oldResult.get<Criterion>())
return false;
Pareto<Types ... > pareto;
return pareto(oldResult, newResult);
}
};
template<>
struct Pareto<>
{
template<typename Map>
bool operator()(Map& oldResult, Map& newResult)
{
oldResult = newResult;
return true;
}
};
int main()
{
TypeMap<double, Minimize<Criterion1>, Maximize<Criterion2>> oldResult, newResult;
Pareto<Minimize<Criterion1>, Maximize<Criterion2>> pareto;
pareto(oldResult, newResult);
}
最佳答案
找到了:
newResult.template set<Criterion>( criterion() );
if(newResult.template get<Criterion>() >= oldResult.template get<Criterion>())
return false;
在这种情况下,您必须为编译器限定成员函数模板。
词法分析器无法决定(在模板声明时,而不是实例化)是否<Criterion
表示模板参数列表 的开始,或者是比较运算符。
见
标准,§ 14.2,子 4. 和 5.,值得注意:
[ Note: As is the case with the typename prefix, the template prefix is allowed in cases where it is not strictly necessary; i.e., when the nested-name-specifier or the expression on the left of the -> or . is not dependent on a template-parameter, or the use does not appear in the scope of a template. —end note ]
关于c++ - 使用模板方法时出现 "expected primary expression"错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/8256636/