An Introduction to Programming in Go/

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Tips on Maps & Errors

Tips on Maps & Errors

Useful tips and tricks for programming in Go.

We'll cover the following...

Sets

You might want to find a way to extract unique value from a collection. In other languages, you often have a set data structure not allowing duplicates. Go doesn’t have that built in, however it’s not too hard to implement (due to a lack of generics, you do need to do that for most types, which can be cumbersome).

Go (1.6.2)
// UniqStr returns a copy if the passed slice with only unique string results.
func UniqStr(col []string) []string {
	m := map[string]struct{}{}
	for _, v := range col {
		if _, ok := m[v]; !ok {
			m[v] = struct{}{}
		}
	}
	list := make([]string, len(m))
	i := 0
	for v := range m {
		list[i] = v
		i++
	}
	return list
}

I used a few interesting tricks that are interesting to know. First, the map of empty structs:

Go (1.6.2)
  m := map[string]struct{}{}

We create a map with the keys being the values we want to be unique, the associated value doesn’t really matter much so it could be anything. For instance:

Go (1.6.2)
  m := map[string]bool{}

However I chose an empty structure because it will be as fast as a boolean but doesn’t allocate as much memory.

The second trick can been seen a bit further:

Go (1.6.2)
if _, ok := m[v]; !ok {
  m[v] = struct{}{}
}

What we are doing here, is simply check if ...