Thread: Providing my own simple iterators

Originally Posted by MutantJohn

Gratned, std::move()'s semantics are entirely over my head. I miss the days when l- and r-value references really were just left and right lol.

It's not that difficult. Well, the basics anyway. You can think of it as all temporaries are r-values and everything else is l-values. R-value references are also l-values.
You can make an l-value into an r-value with std::move. This can be used with local variables, for example.
R-values sort of says "I'm going to be disposed shortly, so you may steal my state." For vectors, this is easy since you can copy over the pointer and size and set the temporary vector's pointer to null.
But consider a coordinate struct. What state do you need to have in the new struct? Everything. So you must copy over all bytes. Hence, in this case, moving doesn't really help.
For advances uses, you can refer to perfect forwarding, which utilizes "universal references."

Returning a local variable is an implicit move in C++11, so you don't need to do it.

O_o

This is true, but there is even more to the situation.

Most C++ compilers, even C++98, implement "RVO" which will, somehow, eliminate the copy.

With C++11, compilers will default to move semantics if available, but may even eliminate the call to the move constructor.

Code:

/* semantically */
void make_point(float x, float y, float z, point * hidden_rvo_this) {
    point::point(hidden_rvo_this, x, y, z);
}

[Edit]

Code:

/* extending the original example */
int main()
{
    point s(make_point(0.0f, 0.0f, 0.0f));
}

Code:

/* may result in something more like this with rvo */
iint main()
{
    char s_hidden[sizeof(point)];
    make_point(0.0f, 0.0f, 0.0f, s);
    point & s(s_hidden);
}

[/Edit]

The example, mutated for explanation from post #27, shows the sort of thing a compiler may do instead of an actual "return" value.

Most compilers will very likely eliminate the copy if you don't specify `std::move' so don't use it for such cases; you may even force a constructor call using `std::move' in such a case depending on the compiler.

Soma

The Point can have as many coordinates as the user wants. Thanks for the all the answers, but I accomplished what I was asked too.

Originally Posted by std10093

The Point can have as many coordinates as the user wants.

Then it's not a point anymore. Unless you are talking about being able to specify the dimension the point exists in.

Originally Posted by Elysia

Then it's not a point anymore. Unless you are talking about being able to specify the dimension the point exists in.

The dimension is an argument of the constructor.

:O
I know saw Soma's post. Where did I say I am good in C++? I am learning.

What? Did I act like knowing better? :P Moreover, it's not for homework. Anyway, these kind of discussions destroy the archive concept.

Originally Posted by MutantJohn

I think it's more your attitude than anything. And how you always make these topics that are secretly homework assignments and then never give enough relevant details. And then when people probe for more information or point out a logical fallacy, you act like you know better and that what you want to do is right even though you directly asked for help. It's exactly that, asking for help and then dismissing it.

Eh, I'm siding with std10093 here. I see no harm. I see it as a member, std10093, who is not super proficient in C++ coming seeking help from other members here.
We all have our flaws. We may not always go about asking for help the right way (hey, it happens, right?), but I haven't seen any attitude that says that std is trying to act superior or ignore advice on purpose.

I think it's more your attitude than anything. And how you always make these topics that are secretly homework assignments and then never give enough relevant details. And then when people probe for more information or point out a logical fallacy, you act like you know better and that what you want to do is right even though you directly asked for help. It's exactly that, asking for help and then dismissing it.

O_o

Could not agree more with the sentiment; third time I've been a participant in his crap.

Eh, I'm siding with std10093 here. I see no harm.

Really? You see no harm?

Code:

std10093: I need help with 'x'.
community: Here is an example of 'x'.
std10093: That will not work.
community: Why?
std10093: Example where 'x' doesn't work.
community: That isn't 'x'; that is 'y'. What are you really doing?
std10093: Let me give you some faulty logic why my example is 'x'; I'm going to do this because I want to ignore your questions.
community: You are wrong. Let me provide many reasons that 'x' is actually 'y'. Now, what are you really doing?
std10093: Okay. Fine, let's us pretend that is 'y'. How do I 'y'?
community: Here is how you 'y'. What are you really doing?
std10093: I can't use 'y'; I didn't tell you that sooner because I didn't think it was relevant.

You see that last bit?

Time and time again in these threads he has been told to provide more information yet does not provide the requested information.

Soma

Originally Posted by phantomotap

Really? You see no harm?

I still see no harm. Perhaps because I am lenient that others. Perhaps because I don't often look inter-posts and quickly forget who posted what. No peeking in history, so to speak.