Help Needed in completing STL-like list class

I have this code here in the following Gist that implements an STL-like list class: https://gist.github.com/DragonOsman/87a1e9fba06d49cab9b5b556c7dd31eb . I need to know how to complete it.

My list constructor that takes a "count" as the parameter isn't being called, so I need help on that as well. But I also need help on erase and insert functions that take a const_iterator parameter instead of a normal iterator parameter. I saw that the standard library has overloads of the erase and insert functions that take a const_iterator and return an iterator. When I try that on VS, I see "<error_type>" as the return type of the function when I try to call it. So I don't understand what to do for that.
I need to know how to complete it
What do you mean by 'complete'. What is missing?

My list constructor that takes a "count" as the parameter isn't being called
What makes you think so?

I saw that the standard library has overloads of the erase and insert functions that take a const_iterator and return an iterator
Since both iterator type have one member Link<Elem> *curr you may create copy constructor/operator for each other. Normally const shouldn't be removed.
What makes you think so?


I tested the constructor (or at least tried to). list<int> lst(6); and list<int> lst{6}; both just give me list of size one with a Link<int> that has a value of 6. It doesn't give me what I want which is a list of size 6 initialized to 0s. As you can see, I even marked that constructor with the keyword "explicit". But that also doesn't help.

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Since both iterator type have one member Link<Elem> *curr you may create copy constructor/operator for each other. Normally const shouldn't be removed. [/quote]  

How will copying the iterator help with erase and insert?  For reference, this is what I'm talking about: 

[quote][code]iterator insert( iterator pos, const T& value );

(until C++11)
iterator insert( const_iterator pos, const T& value );
(since C++11)
iterator insert( const_iterator pos, T&& value );
(2)
(since C++11)

(3)

void insert( iterator pos, size_type count, const T& value );
(until C++11)
iterator insert( const_iterator pos, size_type count, const T& value );
(since C++11)


(4)

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template< class InputIt >
void insert( iterator pos, InputIt first, InputIt last);

(until C++11)
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template< class InputIt >
iterator insert( const_iterator pos, InputIt first, InputIt last );

(since C++11)
iterator insert( const_iterator pos, std::initializer_list<T> ilist );
(5)
(since C++11)
[/quote]

(Taken from cppreference). Notice how the last two take a const_iterator as the first argument but return a normal iterator? That's the overload I want to try adding to my implementation of the class. There's also something similar for erase:

iterator erase( iterator pos );
(until C++11)
iterator erase( const_iterator pos );
(since C++11)


(2)

iterator erase( iterator first, iterator last );
(until C++11)
iterator erase( const_iterator first, const_iterator last );
(since C++11)


As for completing the class. What am I still missing? I don't have emplace and splice operations, and I also don't have an insert function that takes a double reference. What else?
Notice how the last two take a const_iterator as the first argument but return a normal iterator?
Sure, but it is inconsistent.

It doesn't give me what I want which is a list of size 6 initialized to 0s
Acutally you have three constructors that can take a single parameter (line 172, 177, 181). Which is chosen depends on the compiler. It is the first considered matching which depends on the type of Elem. I suggest that you remove the constructor on line 172 and change the constructor on line 181 to
list(size_type count, const Elem &v);.

I even marked that constructor with the keyword "explicit".
The keyword explicit means that this constructor cannot be use in an implicit conversion.
Okay, so wouldn't it be good to make that constructor on line 181 take a default argument as its second parameter? Although, for that, first I need to know if a default parameter can be initialized to the default value of any type T directly in the parameter list. Is this possible?

And could help me with const_iterator erase and insert functions, too, please? The erase function seems to be fine (is it?) but the insert function will have to modify a const iterator which the compiler won't allow. So what should I do there?
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Okay, so wouldn't it be good to make that constructor on line 181 take a default argument as its second parameter?
While theoretically yes, it may depending on the type of Elem confuse the user of the class about what happens when you pass a single value.

Although, for that, first I need to know if a default parameter can be initialized to the default value of any type T directly in the parameter list. Is this possible?
If it has a default constructor: Yes.


And could help me with const_iterator erase and insert functions, too, please?
As I already said. One way to do this is allowing the implicit conversion from one iterator to the other:
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		iterator(const_iterator it)
			: curr{ it.curr } { }
...

		const_iterator(iterator it)
			: curr{ it.curr } { }
Why would it cause confusion? I thought that providing a default argument like that could be a way to provide the illusion of having different constructors when there's really one constructor with the option of not providing less arguments.

Is it possible to do something like list(size_type count, const Elem &v = {}); without the compiler giving an error?
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