ambiguity

问题 Suppose I have this variadic base class-template: template <typename ... Types> class Base { public: // The member foo() can only be called when its template // parameter is contained within the Types ... pack. template <typename T> typename std::enable_if<Contains<T, Types ...>::value>::type foo() { std::cout << "Base::foo()\n"; } }; The foo() member can only be called when its template-parameter matches at least one of the parameters of Base (the implementation of Contains is listed at the

问题 When compiling void ambig( signed long) { } void ambig(unsigned long) { } int main(void) { ambig(-1); return 0; } I get error C2668: 'ambig' : ambiguous call to overloaded function could be 'void ambig(unsigned long)' or 'void ambig(long)' while trying to match the argument list '(int)' I know I can 'fix' it by saying -1L instead of -1 , but why/how exactly is this considered ambiguous in the first place? 回答1: You're passing an int to this overloaded function. Although human intuition says

问题 I have a follow-on question to the problem that the presence of overloaded method definitions with and without parameters leads to a compilation error, which is already discussed here: Why is this reference ambiguous? To recap: trait A { def foo( s: String ) : String def foo : String = foo( "foo" ) } object B extends A { def foo( s: String ) : String = s } B.foo // won't compile results in the error message: error: ambiguous reference to overloaded function both method foo in object B of type

问题 I tried creating a class with one operator bool and one operator void* , but the compiler says they are ambigous. Is there some way I can explain to the compiler what operator to use or can I not have them both? class A { public: operator void*(){ cout << "operator void* is called" << endl; return 0; } operator bool(){ cout << "operator bool is called" << endl; return true; } }; int main() { A a1, a2; if (a1 == a2){ cout << "hello"; } } 回答1: You could call the operator directly. int main() {

问题 I intend this question to be a more generalized question relating to my question found at the following link: Solving design involving multiple inheritance and composite classes in c++ I am working with data sets related to Galaxies. The data about each galaxy will contain information about a galaxie's solar systems, each solar systems planets and each planets moons. The Composite Requirement: From this alone I imagine that I need to use composite class design where I create a class for the

问题 In this question, the following class is defined: public class Program { int n = 0; public void Print() { Console.WriteLine(n); } public Program() { } public Program(int num = 10) { n = num; } } Now, obviously a call to the constructor here using new Program() is ambiguous due to the optional parameter on the second constructor. When reading this its not clear whether n should be initialized with 0 or 10 . However: Actual reporting of the problem seems inconsistent. Setting up this class and

问题 I have written the following earth-shattering application: class SomeA { }; class SomeB { }; class SomeC { }; template <typename A, typename B, typename... Cs> class Foo { public: template <typename U> static void bar(); }; template <typename U> void Foo<SomeA, SomeB, SomeC>::bar() { }; int main() { return 0; } When I compile this (gcc 4.9.3 with -std=c++11 ), I get the following error: a.cpp:10:36: error: ambiguating new declaration of ‘static void Foo<SomeA, SomeB, SomeC>::bar()’ void Foo

问题 I just started using Antlr and am stuck. I have the below grammar and am trying to resolve the ambiguity to parse input like Field:ValueString. expression : Field ':' ValueString; Field : Letter LetterOrDigit*; ValueString : ~[:]; Letter : [a-zA-Z]; LetterOrDigit : [a-zA-Z0-9]; WS: [ \t\r\n\u000C]+ -> skip; suppose a:b is passed in to the grammar, a and b are both identified as Field. How do I resolve this in Antlr4 (C#)? 回答1: You can use a semantic predicate in your lexer rules to perform

问题 As some of you may have noticed, a few hours ago Microsoft released Windows 7 RTM to those of us with a Technet or MSDN subscription. I unfortunately didn't have the opportunity time-wise to test the new OS. I'm asking of anyone who used it with Visual Studio 2008 during RC what was your experience? Did you feel the RC offered a stable environment for it? Did it behave well under Windows 7? In short, can I rely on Windows 7 as my soon-to-be development platform? On another note, did anyone

问题 Why this is non-deterministic and how to fix it? <xs:element name="activeyears"> <xs:complexType> <xs:sequence minOccurs="0" maxOccurs="1"> <xs:sequence minOccurs="0" maxOccurs="unbounded"> <xs:element ref="from" minOccurs="1" maxOccurs="1"/> <xs:element ref="till" minOccurs="1" maxOccurs="1"/> </xs:sequence> <xs:element ref="from" minOccurs="0" maxOccurs="1"/> </xs:sequence> </xs:complexType> </xs:element> It is supposed to mean that <activeyears> is either empty or contains sequence of