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Last active March 21, 2018 16:00
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// We often need our programs to perform operations on
// collections of data, like selecting all items that
// satisfy a given predicate or mapping all items to a new
// collection with a custom function.
// In some languages it's idiomatic to use [generic](http://en.wikipedia.org/wiki/Generic_programming)
// data structures and algorithms. Go does not support
// generics; in Go it's common to provide collection
// functions if and when they are specifically needed for
// your program and data types.
// Here are some example collection functions for slices
// of `strings`. You can use these examples to build your
// own functions. Note that in some cases it may be
// clearest to just inline the collection-manipulating
// code directly, instead of creating and calling a
// helper function.
package main
import "strings"
import "fmt"
// Index returns the first index of the target string `t`, or
// -1 if no match is found.
func IndexOf(vs []string, t string) int {
for i, v := range vs {
if v == t {
return i
}
}
return -1
}
// Include returns `true` if the target string t is in the
// slice.
func Include(vs []string, t string) bool {
return IndexOf(vs, t) >= 0
}
// Any returns `true` if one of the strings in the slice
// satisfies the predicate `f`.
func Any(vs []string, f func(string) bool) bool {
for _, v := range vs {
if f(v) {
return true
}
}
return false
}
// All returns `true` if all of the strings in the slice
// satisfy the predicate `f`.
func All(vs []string, f func(string) bool) bool {
for _, v := range vs {
if !f(v) {
return false
}
}
return true
}
// Filter returns a new slice containing all strings in the
// slice that satisfy the predicate `f`.
func Filter(vs []string, f func(string) bool) []string {
vsf := make([]string, 0)
for _, v := range vs {
if f(v) {
vsf = append(vsf, v)
}
}
return vsf
}
// Map returns a new slice containing the results of applying
// the function `f` to each string in the original slice.
func Map(vs []string, f func(string) string) []string {
vsm := make([]string, len(vs))
for i, v := range vs {
vsm[i] = f(v)
}
return vsm
}
func main() {
// Here we try out our various collection functions.
var strs = []string{"peach", "apple", "pear", "plum"}
fmt.Println(IndexOf(strs, "pear"))
fmt.Println(Include(strs, "grape"))
fmt.Println(Any(strs, func(v string) bool {
return strings.HasPrefix(v, "p")
}))
fmt.Println(All(strs, func(v string) bool {
return strings.HasPrefix(v, "p")
}))
fmt.Println(Filter(strs, func(v string) bool {
return strings.Contains(v, "e")
}))
// The above examples all used anonymous functions,
// but you can also use named functions of the correct
// type.
fmt.Println(Map(strs, strings.ToUpper))
}
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