Why is inheritance of a const/non-const function overload ambiguous?
I was trying to create two classes, the first with a non-const implementation of the functions, the second with a const implementation. Here is a small example:
class Base {
protected:
int some;
};
class A : public virtual Base {
const int& get() const {
return some;
}
};
class B : public virtual Base {
int& get() {
return some;
}
};
class C : public A, B {};
C test;
test.get(); // ambiguous
The call to the get function is ambiguous. No matter that the const version needs to match more requirements. (Calling get on const C is ambiguous as well, but there is one possible function to call.)
Is there a reason for such behaviour in the standard? Thanks!
c++ inheritance overloading multiple-inheritance
edited 5 hours ago
Boann
36.8k1288121
asked 9 hours ago
6yry6e6yry6e
634
New contributor
6yry6e is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
I was trying to create two classes, the first with a non-const implementation of the functions, the second with a const implementation. Here is a small example:
class Base {
protected:
int some;
};
class A : public virtual Base {
const int& get() const {
return some;
}
};
class B : public virtual Base {
int& get() {
return some;
}
};
class C : public A, B {};
C test;
test.get(); // ambiguous
The call to the get function is ambiguous. No matter that the const version needs to match more requirements. (Calling get on const C is ambiguous as well, but there is one possible function to call.)
Is there a reason for such behaviour in the standard? Thanks!
c++ inheritance overloading multiple-inheritance
edited 5 hours ago
Boann
36.8k1288121
asked 9 hours ago
6yry6e6yry6e
634
New contributor
6yry6e is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
stackoverflow.com/questions/5103543/…
– Jesper Juhl
9 hours ago
add a comment |
I was trying to create two classes, the first with a non-const implementation of the functions, the second with a const implementation. Here is a small example:
class Base {
protected:
int some;
};
class A : public virtual Base {
const int& get() const {
return some;
}
};
class B : public virtual Base {
int& get() {
return some;
}
};
class C : public A, B {};
C test;
test.get(); // ambiguous
The call to the get function is ambiguous. No matter that the const version needs to match more requirements. (Calling get on const C is ambiguous as well, but there is one possible function to call.)
Is there a reason for such behaviour in the standard? Thanks!
c++ inheritance overloading multiple-inheritance
edited 5 hours ago
Boann
36.8k1288121
asked 9 hours ago
6yry6e6yry6e
634
New contributor
6yry6e is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I was trying to create two classes, the first with a non-const implementation of the functions, the second with a const implementation. Here is a small example:
class Base {
protected:
int some;
};
class A : public virtual Base {
const int& get() const {
return some;
}
};
class B : public virtual Base {
int& get() {
return some;
}
};
class C : public A, B {};
C test;
test.get(); // ambiguous
The call to the get function is ambiguous. No matter that the const version needs to match more requirements. (Calling get on const C is ambiguous as well, but there is one possible function to call.)
Is there a reason for such behaviour in the standard? Thanks!
c++ inheritance overloading multiple-inheritance
c++ inheritance overloading multiple-inheritance
edited 5 hours ago
Boann
36.8k1288121
asked 9 hours ago
6yry6e6yry6e
634
New contributor
6yry6e is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 5 hours ago
Boann
36.8k1288121
asked 9 hours ago
6yry6e6yry6e
634
New contributor
6yry6e is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 5 hours ago
Boann
36.8k1288121
edited 5 hours ago
Boann
36.8k1288121
edited 5 hours ago
Boann
36.8k1288121
36.8k1288121
asked 9 hours ago
6yry6e6yry6e
634
New contributor
6yry6e is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 9 hours ago
6yry6e6yry6e
634
asked 9 hours ago
6yry6e6yry6e
634
634
New contributor
6yry6e is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
6yry6e is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
6yry6e is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
stackoverflow.com/questions/5103543/…
– Jesper Juhl
9 hours ago
add a comment |
stackoverflow.com/questions/5103543/…
– Jesper Juhl
9 hours ago
stackoverflow.com/questions/5103543/…
– Jesper Juhl
9 hours ago
stackoverflow.com/questions/5103543/…
– Jesper Juhl
9 hours ago
add a comment |
2 Answers
2
active
oldest
votes
Ambiguity occurs when compiler tries to figure out to what entity does the name get refer to, prior to overload resolution. It can be a name of function from class A or from class B. In order to build a list of overloads complier needs to select just one of the classes to pull functions from. In order to fix it you can bring that name from both of the base classes into derived class (and make them public):
class C : public A, public B { public: using A::get; public: using B::get; };
answered 9 hours ago
VTTVTT
24.4k42446
2
An annoying C++ niggle!
– Lightness Races in Orbit
9 hours ago
thanks a lot! c++ in his best... :)
– 6yry6e
9 hours ago
8
An important C++ protection: if adding a function to a base class changed the overload set your code could quietly break; with this rule it breaks noisily.
– Pete Becker
8 hours ago
add a comment |
The problem is that you don't actually have one unified overload-set, in which the mutable variant would be unambiguously best, but two distinct overload-sets, in A and B, and the compiler will not automatically merge them.
Put
using A::get;
using B::get;
in C to merge the overload-sets and thus resolve the ambiguity.
answered 9 hours ago
DeduplicatorDeduplicator
34.3k64888
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
6yry6e is a new contributor. Be nice, and check out our Code of Conduct.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54258524%2fwhy-is-inheritance-of-a-const-non-const-function-overload-ambiguous%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Ambiguity occurs when compiler tries to figure out to what entity does the name get refer to, prior to overload resolution. It can be a name of function from class A or from class B. In order to build a list of overloads complier needs to select just one of the classes to pull functions from. In order to fix it you can bring that name from both of the base classes into derived class (and make them public):
class C : public A, public B { public: using A::get; public: using B::get; };
answered 9 hours ago
VTTVTT
24.4k42446
2
An annoying C++ niggle!
– Lightness Races in Orbit
9 hours ago
thanks a lot! c++ in his best... :)
– 6yry6e
9 hours ago
8
An important C++ protection: if adding a function to a base class changed the overload set your code could quietly break; with this rule it breaks noisily.
– Pete Becker
8 hours ago
add a comment |
Ambiguity occurs when compiler tries to figure out to what entity does the name get refer to, prior to overload resolution. It can be a name of function from class A or from class B. In order to build a list of overloads complier needs to select just one of the classes to pull functions from. In order to fix it you can bring that name from both of the base classes into derived class (and make them public):
class C : public A, public B { public: using A::get; public: using B::get; };
answered 9 hours ago
VTTVTT
24.4k42446
2
An annoying C++ niggle!
– Lightness Races in Orbit
9 hours ago
thanks a lot! c++ in his best... :)
– 6yry6e
9 hours ago
8
An important C++ protection: if adding a function to a base class changed the overload set your code could quietly break; with this rule it breaks noisily.
– Pete Becker
8 hours ago
add a comment |
Ambiguity occurs when compiler tries to figure out to what entity does the name get refer to, prior to overload resolution. It can be a name of function from class A or from class B. In order to build a list of overloads complier needs to select just one of the classes to pull functions from. In order to fix it you can bring that name from both of the base classes into derived class (and make them public):
class C : public A, public B { public: using A::get; public: using B::get; };
answered 9 hours ago
VTTVTT
24.4k42446
Ambiguity occurs when compiler tries to figure out to what entity does the name get refer to, prior to overload resolution. It can be a name of function from class A or from class B. In order to build a list of overloads complier needs to select just one of the classes to pull functions from. In order to fix it you can bring that name from both of the base classes into derived class (and make them public):
class C : public A, public B { public: using A::get; public: using B::get; };
answered 9 hours ago
VTTVTT
24.4k42446
edited 9 hours ago
answered 9 hours ago
VTTVTT
24.4k42446
answered 9 hours ago
VTTVTT
24.4k42446
answered 9 hours ago
VTTVTT
24.4k42446
24.4k42446
2
An annoying C++ niggle!
– Lightness Races in Orbit
9 hours ago
thanks a lot! c++ in his best... :)
– 6yry6e
9 hours ago
8
An important C++ protection: if adding a function to a base class changed the overload set your code could quietly break; with this rule it breaks noisily.
– Pete Becker
8 hours ago
add a comment |
2
An annoying C++ niggle!
– Lightness Races in Orbit
9 hours ago
thanks a lot! c++ in his best... :)
– 6yry6e
9 hours ago
8
An important C++ protection: if adding a function to a base class changed the overload set your code could quietly break; with this rule it breaks noisily.
– Pete Becker
8 hours ago
2
2
An annoying C++ niggle!
– Lightness Races in Orbit
9 hours ago
An annoying C++ niggle!
– Lightness Races in Orbit
9 hours ago
thanks a lot! c++ in his best... :)
– 6yry6e
9 hours ago
thanks a lot! c++ in his best... :)
– 6yry6e
9 hours ago
8
8
An important C++ protection: if adding a function to a base class changed the overload set your code could quietly break; with this rule it breaks noisily.
– Pete Becker
8 hours ago
An important C++ protection: if adding a function to a base class changed the overload set your code could quietly break; with this rule it breaks noisily.
– Pete Becker
8 hours ago
add a comment |
The problem is that you don't actually have one unified overload-set, in which the mutable variant would be unambiguously best, but two distinct overload-sets, in A and B, and the compiler will not automatically merge them.
Put
using A::get;
using B::get;
in C to merge the overload-sets and thus resolve the ambiguity.
answered 9 hours ago
DeduplicatorDeduplicator
34.3k64888
add a comment |
The problem is that you don't actually have one unified overload-set, in which the mutable variant would be unambiguously best, but two distinct overload-sets, in A and B, and the compiler will not automatically merge them.
Put
using A::get;
using B::get;
in C to merge the overload-sets and thus resolve the ambiguity.
answered 9 hours ago
DeduplicatorDeduplicator
34.3k64888
add a comment |
The problem is that you don't actually have one unified overload-set, in which the mutable variant would be unambiguously best, but two distinct overload-sets, in A and B, and the compiler will not automatically merge them.
Put
using A::get;
using B::get;
in C to merge the overload-sets and thus resolve the ambiguity.
answered 9 hours ago
DeduplicatorDeduplicator
34.3k64888
The problem is that you don't actually have one unified overload-set, in which the mutable variant would be unambiguously best, but two distinct overload-sets, in A and B, and the compiler will not automatically merge them.
Put
using A::get;
using B::get;
in C to merge the overload-sets and thus resolve the ambiguity.
answered 9 hours ago
DeduplicatorDeduplicator
34.3k64888
answered 9 hours ago
DeduplicatorDeduplicator
34.3k64888
answered 9 hours ago
DeduplicatorDeduplicator
34.3k64888
answered 9 hours ago
DeduplicatorDeduplicator
34.3k64888
34.3k64888
add a comment |
add a comment |
6yry6e is a new contributor. Be nice, and check out our Code of Conduct.
6yry6e is a new contributor. Be nice, and check out our Code of Conduct.
6yry6e is a new contributor. Be nice, and check out our Code of Conduct.
6yry6e is a new contributor. Be nice, and check out our Code of Conduct.
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f54258524%2fwhy-is-inheritance-of-a-const-non-const-function-overload-ambiguous%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
stackoverflow.com/questions/5103543/…
– Jesper Juhl
9 hours ago