Warp escribió:
> Nicolas Alvarez <nic### [at] gmailisthebestcom> wrote:
>> Ahh, then I can say I did figure out both.
> 
>   Ok, if you want a harder puzzle, here's a curious quirk about C++ (not
> related to memory leaks, though):
> 
> //------------------------------------------------------------------------
> #include <map>
> 
> struct A { int i; };
> 
> struct Comp
> { bool operator()(const A& a1, const A& a2) const { return a1.i < a2.i; }
> };
> 
> int main()
> {
>     std::map<A, int, Comp> theMap(Comp());
>     A a = { 1 };
>     theMap[a] = 5;
> }

Hrm, I never used map myself. I think I'll go search documentation on 
what the template parameters are.

> a) This doesn't compile. Without using a compiler, can you tell where
>    is the problem and what is the exact reason why it doesn't compile?
 >
> b) If you can't see it, try it with a compiler. I bet you still can't see
>    the problem... :P
> 
> c) In the erroneous line, can you tell me exactly what that line means?
> 
> d) What is the easiest way (smallest amount of extra code) to make it
>    compile and work as expected?

Oh I think I know. I took a while without noticing anything wrong, but 
now I remember having read about it in C++ FAQ Lite. theMap(Comp()) 
*declares a function* instead of instantiating an object. Good to know 
all the time I wast^H^H^H^H spent reading that website was actually useful.

Okay, *after* remembering that and writing that paragraph, I went and 
searched for what I remembered having read. Maybe that counts as 
cheating... I wouldn't have searched if I had read question D before, so 
I could try figuring out the solution myself :)

http://www.parashift.com/c++-faq-lite/ctors.html#faq-10.2

The solution is:
std::map<A, int, Comp> theMap = Comp();

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