How to run non const methods on nested objects in Composition /Aggregation pattern in C++?
I came to from the C# world and, thanks to the "Properties", I can run a setter method on a nested object without leaking any internals like this:
objectA.objectB.objectC.SetSomething();
So far, I found that the best analog in C++ is to use getters and get nested object by value or const reference than use setters to set them by value. But this would result in the following code:
auto b = objectA().getObjectB();
auto c = b.getObjectC();
c.SetSomething();
b.setObjectC(c);
objectA.setObjectB(b);
Not only this is 5 lines instead of one, but it involves multiple copies of the nested objects in b.setObjectC(c); and objectA.setObjectB(b);
I can let the getters to return a non-const reference of a nested object (or use public variables) and will be able to write in C++:
objectA.objectB.objectC.SetSomething();
But, instantly I get the ability to set objectB without objectA knowledge like this:
objectA.objectB = b {};
And this is unacceptable in aggregation pattern where a parent object initializes the nested object.
Other two approaches I read about:
Instead of aggregation, use multiple protected inheritances and
translate needed methods with "using". However, I also read in
"Google C++ Style Guide" to never use protected inheritance..Rewrite all required methods in the parent class manually. But this
would require for me to write SetSomething() method in both ObjectB
an objectA which, in my opinion, violates "Don't repeat
yourself".
What am I missing? How can this be done? Could anyone please shed some light.
Thanks in advance.
c++11
asked yesterday
dazipe
12
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dazipe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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add a comment |
I came to from the C# world and, thanks to the "Properties", I can run a setter method on a nested object without leaking any internals like this:
objectA.objectB.objectC.SetSomething();
So far, I found that the best analog in C++ is to use getters and get nested object by value or const reference than use setters to set them by value. But this would result in the following code:
auto b = objectA().getObjectB();
auto c = b.getObjectC();
c.SetSomething();
b.setObjectC(c);
objectA.setObjectB(b);
Not only this is 5 lines instead of one, but it involves multiple copies of the nested objects in b.setObjectC(c); and objectA.setObjectB(b);
I can let the getters to return a non-const reference of a nested object (or use public variables) and will be able to write in C++:
objectA.objectB.objectC.SetSomething();
But, instantly I get the ability to set objectB without objectA knowledge like this:
objectA.objectB = b {};
And this is unacceptable in aggregation pattern where a parent object initializes the nested object.
Other two approaches I read about:
Instead of aggregation, use multiple protected inheritances and
translate needed methods with "using". However, I also read in
"Google C++ Style Guide" to never use protected inheritance..Rewrite all required methods in the parent class manually. But this
would require for me to write SetSomething() method in both ObjectB
an objectA which, in my opinion, violates "Don't repeat
yourself".
What am I missing? How can this be done? Could anyone please shed some light.
Thanks in advance.
c++11
asked yesterday
dazipe
12
New contributor
dazipe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
provide bothconstand non-constgetters? Or, if you happen to use particular nested method quite often, simply provide it in your most-outer class and implement it by calling the inner-object version?
– Fureeish
yesterday
Just write getters that return non-const references. It's not uncommon to end up writing 2 getters for some members, one returning a const reference (which should be the default) and one returning a non-const reference (sometimes people suffix the namegetFooNC()to differentiate the two)
– JMAA
yesterday
This is whole point... Providing non const getter provides full access to the object. Not only can I call non const methods but I can also replace the object itself. Ex objectA.objectB = new b {}; In aggregation pattern where parent object initializes nested object with some special properties this should not be allowed.
– dazipe
22 hours ago
IfgetObjectB()returns a non-constb&reference, thenobjectA.getObjectB() = new b {}won't compile. You would, however, be able to writeobjectA.getObjectB().getObjectC().SetSomething(), Is this not what you want?
– Igor Tandetnik
19 hours ago
SinceobjectA.getObjectB()reterns a reference to an object it is an lvalue. TheobjectA.getObjectB() = b {};(without new) compiles just fine. It is equivalent tob& tempB = objectA.getObjectB() ; tempB = b {};. And in the end I'm able to replace the ObjectB inside ObjectA skipping any type of internal logic.
– dazipe
17 hours ago
add a comment |
I came to from the C# world and, thanks to the "Properties", I can run a setter method on a nested object without leaking any internals like this:
objectA.objectB.objectC.SetSomething();
So far, I found that the best analog in C++ is to use getters and get nested object by value or const reference than use setters to set them by value. But this would result in the following code:
auto b = objectA().getObjectB();
auto c = b.getObjectC();
c.SetSomething();
b.setObjectC(c);
objectA.setObjectB(b);
Not only this is 5 lines instead of one, but it involves multiple copies of the nested objects in b.setObjectC(c); and objectA.setObjectB(b);
I can let the getters to return a non-const reference of a nested object (or use public variables) and will be able to write in C++:
objectA.objectB.objectC.SetSomething();
But, instantly I get the ability to set objectB without objectA knowledge like this:
objectA.objectB = b {};
And this is unacceptable in aggregation pattern where a parent object initializes the nested object.
Other two approaches I read about:
Instead of aggregation, use multiple protected inheritances and
translate needed methods with "using". However, I also read in
"Google C++ Style Guide" to never use protected inheritance..Rewrite all required methods in the parent class manually. But this
would require for me to write SetSomething() method in both ObjectB
an objectA which, in my opinion, violates "Don't repeat
yourself".
What am I missing? How can this be done? Could anyone please shed some light.
Thanks in advance.
c++11
asked yesterday
dazipe
12
New contributor
dazipe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I came to from the C# world and, thanks to the "Properties", I can run a setter method on a nested object without leaking any internals like this:
objectA.objectB.objectC.SetSomething();
So far, I found that the best analog in C++ is to use getters and get nested object by value or const reference than use setters to set them by value. But this would result in the following code:
auto b = objectA().getObjectB();
auto c = b.getObjectC();
c.SetSomething();
b.setObjectC(c);
objectA.setObjectB(b);
Not only this is 5 lines instead of one, but it involves multiple copies of the nested objects in b.setObjectC(c); and objectA.setObjectB(b);
I can let the getters to return a non-const reference of a nested object (or use public variables) and will be able to write in C++:
objectA.objectB.objectC.SetSomething();
But, instantly I get the ability to set objectB without objectA knowledge like this:
objectA.objectB = b {};
And this is unacceptable in aggregation pattern where a parent object initializes the nested object.
Other two approaches I read about:
Instead of aggregation, use multiple protected inheritances and
translate needed methods with "using". However, I also read in
"Google C++ Style Guide" to never use protected inheritance..Rewrite all required methods in the parent class manually. But this
would require for me to write SetSomething() method in both ObjectB
an objectA which, in my opinion, violates "Don't repeat
yourself".
What am I missing? How can this be done? Could anyone please shed some light.
Thanks in advance.
c++11
c++11
asked yesterday
dazipe
12
New contributor
dazipe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked yesterday
dazipe
12
New contributor
dazipe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
edited 4 hours ago
asked yesterday
dazipe
12
New contributor
dazipe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked yesterday
dazipe
12
asked yesterday
dazipe
12
12
New contributor
dazipe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
dazipe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
dazipe is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
provide bothconstand non-constgetters? Or, if you happen to use particular nested method quite often, simply provide it in your most-outer class and implement it by calling the inner-object version?
– Fureeish
yesterday
Just write getters that return non-const references. It's not uncommon to end up writing 2 getters for some members, one returning a const reference (which should be the default) and one returning a non-const reference (sometimes people suffix the namegetFooNC()to differentiate the two)
– JMAA
yesterday
This is whole point... Providing non const getter provides full access to the object. Not only can I call non const methods but I can also replace the object itself. Ex objectA.objectB = new b {}; In aggregation pattern where parent object initializes nested object with some special properties this should not be allowed.
– dazipe
22 hours ago
IfgetObjectB()returns a non-constb&reference, thenobjectA.getObjectB() = new b {}won't compile. You would, however, be able to writeobjectA.getObjectB().getObjectC().SetSomething(), Is this not what you want?
– Igor Tandetnik
19 hours ago
SinceobjectA.getObjectB()reterns a reference to an object it is an lvalue. TheobjectA.getObjectB() = b {};(without new) compiles just fine. It is equivalent tob& tempB = objectA.getObjectB() ; tempB = b {};. And in the end I'm able to replace the ObjectB inside ObjectA skipping any type of internal logic.
– dazipe
17 hours ago
add a comment |
provide bothconstand non-constgetters? Or, if you happen to use particular nested method quite often, simply provide it in your most-outer class and implement it by calling the inner-object version?
– Fureeish
yesterday
Just write getters that return non-const references. It's not uncommon to end up writing 2 getters for some members, one returning a const reference (which should be the default) and one returning a non-const reference (sometimes people suffix the namegetFooNC()to differentiate the two)
– JMAA
yesterday
This is whole point... Providing non const getter provides full access to the object. Not only can I call non const methods but I can also replace the object itself. Ex objectA.objectB = new b {}; In aggregation pattern where parent object initializes nested object with some special properties this should not be allowed.
– dazipe
22 hours ago
IfgetObjectB()returns a non-constb&reference, thenobjectA.getObjectB() = new b {}won't compile. You would, however, be able to writeobjectA.getObjectB().getObjectC().SetSomething(), Is this not what you want?
– Igor Tandetnik
19 hours ago
SinceobjectA.getObjectB()reterns a reference to an object it is an lvalue. TheobjectA.getObjectB() = b {};(without new) compiles just fine. It is equivalent tob& tempB = objectA.getObjectB() ; tempB = b {};. And in the end I'm able to replace the ObjectB inside ObjectA skipping any type of internal logic.
– dazipe
17 hours ago
provide both
const and non-const getters? Or, if you happen to use particular nested method quite often, simply provide it in your most-outer class and implement it by calling the inner-object version?– Fureeish
yesterday
provide both
const and non-const getters? Or, if you happen to use particular nested method quite often, simply provide it in your most-outer class and implement it by calling the inner-object version?– Fureeish
yesterday
Just write getters that return non-const references. It's not uncommon to end up writing 2 getters for some members, one returning a const reference (which should be the default) and one returning a non-const reference (sometimes people suffix the name
getFooNC() to differentiate the two)– JMAA
yesterday
Just write getters that return non-const references. It's not uncommon to end up writing 2 getters for some members, one returning a const reference (which should be the default) and one returning a non-const reference (sometimes people suffix the name
getFooNC() to differentiate the two)– JMAA
yesterday
This is whole point... Providing non const getter provides full access to the object. Not only can I call non const methods but I can also replace the object itself. Ex objectA.objectB = new b {}; In aggregation pattern where parent object initializes nested object with some special properties this should not be allowed.
– dazipe
22 hours ago
This is whole point... Providing non const getter provides full access to the object. Not only can I call non const methods but I can also replace the object itself. Ex objectA.objectB = new b {}; In aggregation pattern where parent object initializes nested object with some special properties this should not be allowed.
– dazipe
22 hours ago
If
getObjectB() returns a non-const b& reference, then objectA.getObjectB() = new b {} won't compile. You would, however, be able to write objectA.getObjectB().getObjectC().SetSomething(), Is this not what you want?– Igor Tandetnik
19 hours ago
If
getObjectB() returns a non-const b& reference, then objectA.getObjectB() = new b {} won't compile. You would, however, be able to write objectA.getObjectB().getObjectC().SetSomething(), Is this not what you want?– Igor Tandetnik
19 hours ago
Since
objectA.getObjectB() reterns a reference to an object it is an lvalue. The objectA.getObjectB() = b {}; (without new) compiles just fine. It is equivalent to b& tempB = objectA.getObjectB() ; tempB = b {};. And in the end I'm able to replace the ObjectB inside ObjectA skipping any type of internal logic.– dazipe
17 hours ago
Since
objectA.getObjectB() reterns a reference to an object it is an lvalue. The objectA.getObjectB() = b {}; (without new) compiles just fine. It is equivalent to b& tempB = objectA.getObjectB() ; tempB = b {};. And in the end I'm able to replace the ObjectB inside ObjectA skipping any type of internal logic.– dazipe
17 hours ago
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provide both
constand non-constgetters? Or, if you happen to use particular nested method quite often, simply provide it in your most-outer class and implement it by calling the inner-object version?– Fureeish
yesterday
Just write getters that return non-const references. It's not uncommon to end up writing 2 getters for some members, one returning a const reference (which should be the default) and one returning a non-const reference (sometimes people suffix the name
getFooNC()to differentiate the two)– JMAA
yesterday
This is whole point... Providing non const getter provides full access to the object. Not only can I call non const methods but I can also replace the object itself. Ex objectA.objectB = new b {}; In aggregation pattern where parent object initializes nested object with some special properties this should not be allowed.
– dazipe
22 hours ago
If
getObjectB()returns a non-constb&reference, thenobjectA.getObjectB() = new b {}won't compile. You would, however, be able to writeobjectA.getObjectB().getObjectC().SetSomething(), Is this not what you want?– Igor Tandetnik
19 hours ago
Since
objectA.getObjectB()reterns a reference to an object it is an lvalue. TheobjectA.getObjectB() = b {};(without new) compiles just fine. It is equivalent tob& tempB = objectA.getObjectB() ; tempB = b {};. And in the end I'm able to replace the ObjectB inside ObjectA skipping any type of internal logic.– dazipe
17 hours ago