CODEWITHSUNDEEP
c++c++11
IceFire
IceFire

Reputation: 4137

Range-based for over pair list

Say, I want to iterate a number of pairs defined inline. Is there a shorter way to write:

for(auto pair : std::initializer_list<std::pair<int,int>>{{1,2}, {3,4}})
    // ...

?

Upvotes: 9

Views: 3732

Answers (2)

StoryTeller - Unslander Monica
StoryTeller - Unslander Monica

Reputation: 170163

Just specify the first element is a pair. The rest will be deduced automatically:

for(auto& pair : {std::pair<int,int>{1,2}, {3,4}})
  ;

The braced enclosed initializer is deduced to be std::initalizer_list, and the first element being named a pair will require all elements to be an initalizer for a pair.

You tagged C++11, but for completeness, it can be even shorter in C++17:

for(auto& pair : {std::pair{1,2}, {3,4}})
  ;

Due to class template argument deduction. If you don't have that, than std::make_pair will do if you want to maintain the benefits of template argument deduction:

for(auto& pair : {std::make_pair(1,2), {3,4}})
  ;

Though ostensibly, it isn't as useful for code golfing as the C++17 version.

Upvotes: 15

Galik
Galik

Reputation: 48635

The good ol' type alias:

using pairlist = std::initializer_list<std::pair<int,int>>;

for(auto pair : pairlist{{1,2}, {3,4}})
{
    // stuff happens here
}

Upvotes: 3

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