=?UTF-8?Q?Re=3A_Is_a_string_literal_an_lvalue=EF=BC=9F?=
On Oct 8, 4:22 pm, Stanley Rice wrote:
On Oct 8, 7:13 pm, SG wrote:
GLvalues versus PRvalues:
-------------------------
GLvalues refer to objects that have an identity (region of storage)
PRvalues refer to plain values or temporary objects
3.10.----------------------
An rvalue is an xvalue, a temporary object or subobject thereof, or a
value that is not associated with an object.
A prvalue is an rvalue that is not an xvalue.
------------------------------
so, should prvalue includes subobject? But I don't understand what a
subobject here means.
Non-static data members and the base-class portions of class-type
objects as well as elements of an array are considered subobjects.
[GLvalue <-> PRvalue]
This "axis" affects things like polymorphism, ability to take the
address of an object. GLvalues can have an abstract or incomplete
static type. [...]
Here what do you mean by 'abstract type'? I referred to the SO, but
found nothing.
In the context of C++, I use "abstract type" to mean a polymorphic
type that cannot be directly instantiated because it has at least one
*pure* virtual function. A polymorphic type is a type that has at
least one virtual member function or destructor.
[...]
Examples:
string source();
int main() {
source(); // PRvalue
string x = "yay";
x; // Lvalue
move(x) // Xvalue (still refers to the same object b=
ut
// the expression has a different va=
lue category)
I cannot under the statement above. why the 'x' here is xvalue?
It is not. The whole expression -- std::move(x) -- is an Xvalue. The
subexpression x will always be an Lvalue in that scope.
[...]
Actually, I could not understand the whole paragraph of the standard,
for I just began to read standard for a several days.
[...]
All in all, greatly thanks for your detail explanation. The standard
is new to me, and there are lots of new terms that I haven't heard
before. Any suggestions to how to read it?
Sorry, no. It requires some iterations, back & forth and time to get
the hang of it. If you're interested in learning basic C++ there are
much better books than that. If you're interested in learning about
the new features, try to look for articles explaining these features
written by knowledgable people. Books have yet to be written. The
lvalue/rvalue/move semantics topic is covered in a couple of articles
as well as talks that have been recorded and are publicly available.
Authors and speakers include Dave Abrahams, Howard Hinnant, Scott
Meyers, Stephan T. Lavavej.
Cheers!
SG