72 lines
1.8 KiB
Go
72 lines
1.8 KiB
Go
// _Maps_ are Go's built-in [associative data type](https://en.wikipedia.org/wiki/Associative_array)
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// (sometimes called _hashes_ or _dicts_ in other languages).
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package main
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import (
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"fmt"
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"maps"
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)
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func main() {
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// To create an empty map, use the builtin `make`:
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// `make(map[key-type]val-type)`.
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m := make(map[string]int)
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// Set key/value pairs using typical `name[key] = val`
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// syntax.
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m["k1"] = 7
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m["k2"] = 13
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// Printing a map with e.g. `fmt.Println` will show all of
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// its key/value pairs.
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fmt.Println("map:", m)
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// Get a value for a key with `name[key]`.
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v1 := m["k1"]
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fmt.Println("v1:", v1)
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// If the key doesn't exist, the
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// [zero value](https://go.dev/ref/spec#The_zero_value) of the
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// value type is returned.
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v3 := m["k3"]
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fmt.Println("v3:", v3)
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// The builtin `len` returns the number of key/value
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// pairs when called on a map.
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fmt.Println("len:", len(m))
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// The builtin `delete` removes key/value pairs from
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// a map.
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delete(m, "k2")
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fmt.Println("map:", m)
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// To remove *all* key/value pairs from a map, use
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// the `clear` builtin.
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clear(m)
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fmt.Println("map:", m)
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// The optional second return value when getting a
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// value from a map indicates if the key was present
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// in the map. This can be used to disambiguate
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// between missing keys and keys with zero values
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// like `0` or `""`. Here we didn't need the value
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// itself, so we ignored it with the _blank identifier_
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// `_`.
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_, prs := m["k2"]
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fmt.Println("prs:", prs)
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// You can also declare and initialize a new map in
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// the same line with this syntax.
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n := map[string]int{"foo": 1, "bar": 2}
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fmt.Println("map:", n)
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// The `maps` package contains a number of useful
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// utility functions for maps.
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n2 := map[string]int{"foo": 1, "bar": 2}
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if maps.Equal(n, n2) {
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fmt.Println("n == n2")
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}
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}
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