Hi, ----- Original Message ----- From: "Gennadiy Rozental" <rogeeff@gmail.com> To: <boost@lists.boost.org> Sent: Wednesday, October 21, 2009 10:50 PM Subject: Re: [boost] [property] interest in C# like properties for C++?
A.X() = B.X() = 5 isn't horrible, but A.X = B.X = 5 is what one expects when one thinks of "properties."
Sorry, if I jump in in the middle of the discussion.
Boost.Test uses properties with syntax like this:
int i = a.p_X;
a.p_X.value = 1;
This syntax IMO has couple advantages:
1. From encapsulation standpoint this is as good as having explicit setter and getter.
2. I do not like to allow a.p_X = 1. ".value" syntax allows me to grep easily for all the encounters of property modification. This is especially useful in situations where there are myriads of read-only access and only couple mutating ones.
3. Single line definition:
readwrite_property<int> p_X;
Instead of 3 lines required by data member, getter and setter.
4. I also have readonly_property, which can restrict mutating access to the property value for all classes (in which case property initialized in a constructor once and never changes). Or I can have readonly property with fixed list of classes allowed mutating access.
I would name your class readwrite_data<> and read_only_data<> as there is no possibility to provide accessors, or are there? The main aim of a Property is exactly that, ability to provide read/write accessors to some property. I don't like too much your use of the .value to repere assignements, as the user can also use it to get the value. If you want to repare assignation to a data you should use a explicit function. I see one advantage to wrap some data type in a readwrite<T> or readonly<T> is that these classes can provide several styles: * Behave like builtin types (transparent): use assignement and conversion operators a.p_X = 1; i = a.p_X * Function like syntax for both setters and getters: use operator() to get reference or value a.p_X()=1; i = a.p_X(); * Different setter/getter methods names a.p_X.set_value(1); i = a.p_X.get_value(); Whether a single class should provide all the styles or only a particular need to be analysed, as each style has its own advantage and liabilities. Note for example that, set_value is reperable and can not be used to get the value and get_value is not ambiguous. Another way to repare the assignements is to use a free function assign_to, like we use swap, but this is out of the scope of this thread, so I will start a new one. Best, Vicente