golang why don t we have a set datastructure

Question

I m trying to solve  The go programming lanaguage  exercise  1 4 which requires me to have a set  I can create a set type but why doesn t the language come with one   go  having come from google  where guava also originated  why didn t the language designers opt for adding support for fundamental data structures   why force your users to create their own implementations for something so basic as a set

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Partly  because Go doesn t have generics  so you would need one set-type for every type  or fall back on reflection  which is rather inefficient    Partly  because if all you need is  add remove individual elements to a set  and  relatively space-efficient   you can get a fair bit of that simply by using a map yourtype bool  and set the value to true for any element in the set  or  for more space efficiency  you can use an empty struct as the value and use    present   the setoid key  to check for presence

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Like Vatine wrote  Since go lacks generics it would have to be part of the language and not the standard library  For that you would then have to pollute the language with keywords set  union  intersection  difference  subset     The other reason is  that it s not clear at all what the  right  implementation of a set is    There is a functional approach   func IsInEvenNumbers n int  bool       if n   2    0           return true          return false      This is a set of all even ints  It has a very efficient lookup and union  intersect  difference and subset can easily be done by functional composition    Or you do a has-like approach like Dali showed    A map does not have that problem  since you store something associated with the value

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Another possibility is to use bit sets  for which there is at least one package or you can use the built-in big package  In this case  basically you need to define a way to convert your object to an index

User · Answer

One reason is that it is easy to create a set from map   s    map int bool 5  true  2  true     ok    s 6     check for existence s 8    true    add element  delete s  2     remove element   Union  s union    map int bool   for k       range s1      s union k    true   for k       range s2      s union k    true     Intersection  s intersection    map int bool   for k      range s1      if s2 k        s intersection k    true         It is not really that hard to implement all other set operations

[data-structures] golang why don't we have a set datastructure

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