On Fri, 20 Jan 2012 04:29:12 -0500, Peter Alexander
<[email protected]> wrote:
On 20/01/12 12:57 AM, Steven Schveighoffer wrote:
On Thu, 19 Jan 2012 18:41:44 -0500, Andrei Alexandrescu
<[email protected]> wrote:
On 1/19/12 4:43 PM, Steven Schveighoffer wrote:
On Thu, 19 Jan 2012 14:06:00 -0500, torhu <[email protected]> wrote:
If the type of byKeys is Range, I would expect to be able to treat it
like one. Not like one, then another, then another, then another...
ad
infinitum.
I don't know what you mean. You can treat it like one.
-Steve
It's the rvalue aspect. byKey does not hold a range inside the
hashtable (as a member variable would do). Each use of byKey gives you
a range that you get to iterate from the beginning.
The point of a property is to allow for read-only access on something
that is logically a property but can only be implemented via a function.
byKeys is such a property. There is no way to specify a field that
behaves the same. This doesn't make properties invalid or useless.
Can you define what "is logically a property means"? (I assume you meant
"field" there)
No, I meant property. A property is a more general term. It's a piece of
data that is associated with an entity. For example, if you have a ball,
you might say that the ball is red, or it's bouncy. Those are
properties. In this context (of programming language properties), a
property can also be a piece of the entity. For example, the valve stem
in the ball.
properties do several things:
1. they allow you to avoid storing logically derived data. For example,
if I have x and y, and I want to get z = sqrt(x*x + y*y), then I could
either store z as a field, and update it every time x and y are changed,
or I can just make a property, which logically acts like a read-only field.
2. they allow encapsulation. This means, I can give you information or
mutable pieces of data from an object without actually exposing the data
to you directly.
3. They allow you to control read/write access to a piece of data,
including using contracts to check for errors.
byKey is an example of the first -- it's not directly stored, but is
generated on request. Since it's not actually stored in the object, the
other 2 features don't apply. Which is why I was confused as to the
nature of the argument above, it's a derived piece of data. The very
nature of calculated properties are that you don't get direct access to
the internal data because it doesn't exist!
-Steve
