Renaming first and second of a map iterator

问题:

Is there any way to rename the first and second accessor functions of a map iterator. I understand they have these names because of the underlying pair which represents the key and value, but I'd like the iterators to be a little more readable. I think this might be possible using an iterator adaptor, but I'm not sure how to implement it.

Please note that I can't use boost.

Example of what I mean:

map adjacency_list; for(map::iterator it = adjacency_list.begin();     it != adjacency_list.end();     ++it) {     Vertex v = it->first;     //instead I would like to have it->vertex } 

回答1:

If you're just concerned about readability you could do something like this:

typedef map AdjacencyList; struct adjacency {     adjacency(AdjacencyList::iterator& it)        : vertex(it->first), edge(it->second) {}     Vertex& vertex;     Edge& edge; }; 

And then:

Vertex v = adjacency(it).vertex; 

回答2:

You can't rename the members, but you can have some functions to help.

inline Vertex& vertex(map::iterator& it) {return it->first;} inline Edge& edge(map::iterator& it) {return it->second;} 

Then, instead of it->vertex like you want, you can do vertex(it)

回答3:

Unfortunately, no. What I usually do is this:

typedef map AdjacencyList; typedef AdjacencyList::value_type Vertex_Edge_Pair; 

For readability. Inside your loop you can also say

Vertex& current_vertex = it->first; Edge& current_edge = it->second; 

回答4:

Sure, reimplement or wrap iterator, but is it worth the effort? Wouldn't

Vertex& v = it->first; 

be easier?

回答5:

I wouldn't recommend really using this, but it does seem to work, at least to the minimum degree of the test program doing what I wanted/expected:

#include 

回答6:

I liked KeithB's solution with free functions. However, a more reusable solution might be nice.

What about function objects that access first or second, as you can name the instances anything you like:

#include 

This is the best I could do. I also tried to make those functors accept the iterator directly, but one way or another this means that the signature will contain dependent names which apparently makes template type deduction impossible (I couldn't find a way to overload GetSecond for iterator/const_iterator even with deferred return type of C++0x).

回答7:

I've got an evil solution!

#define vertex first #define edge second 

Although as an evil solution it will doubtless cause great trauma and difficult to diagnose compilation problems when you accidentally use those words elsewhere.

Added for completeness.

Can't believe nobody else has suggested this.

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