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POIdiomatic way to implement generic functions in Go
 

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    <p>Let's say I want to write a function to check whether a predicate is matched for an element in a slice:</p> <pre><code>func IsIn(array []T, pred func(elt T) bool) bool { for _, obj := range array { if pred(obj) { return true;} } return false; } </code></pre> <p>Obviously, the previous code won't compile, since <code>T</code> does not exist. I can replace it with some <code>interface{}</code> like this:</p> <pre><code>func IsIn(array[]interface{}, pred func(elt interface{}) bool) bool { ... } </code></pre> <p>As I am happy to let the predicate perform the casting:</p> <pre><code>IsIn([]interface{}{1,2,3,4}, func(o interface{}) {return o.(int) == 3; }); </code></pre> <p>But then, the function won't accept any array which is not of type <code>[]interface{}</code>:</p> <pre><code>IsIn([]int{1,2,3,4}, func(o interface{}) { return o.(int) == 3; }) // DO NOT COMPILE </code></pre> <p>And similarly:</p> <pre><code>func IsIn(arr interface, pred func(o interface{}) bool) bool { for _, o := range arr.([]interface{}) { ... } } IsIn([]int{1,2,3,4}, func(o interface{}) { return o.(int) == 3; }) // PANICS AT RUNTIME (cannot cast []int to []interface) </code></pre> <p>The other alternative is to have typed functions for each array type:</p> <pre><code>IsInInt(arr []int, pred func(i int) bool) { ... } IsInStr(arr []string, pred func(s string) bool) { ... } ... </code></pre> <p>But it seems like a LOT of code duplication.</p> <p>Has anyone come up with an nice way to deal with such situations ?</p> <p><strong>EDIT</strong></p> <p>Thanks to <a href="https://stackoverflow.com/users/1065241/jnml">jnml</a>'s fantastic tips on Go reflection, I think I have found a nice way to express these patterns, by converting every 'iterable' to a channel:</p> <pre><code>func iter(obj interface{}) chan interface{} { c := make(chan interface{}) v := reflect.ValueOf(obj) if (v.Kind() == reflect.Array || v.Kind() == reflect.Slice) { go func() { for i := 0; i &lt; v.Len(); i++ { c&lt;-v.Index(i).Interface() } close(c) }() } else if v.Kind() == reflect.Chan { go func() { x, ok := v.Recv() for ok { c&lt;-x.Interface() x,ok = v.Recv() } close(c) }() } else if (... whatever iteration protocol you have ...) { } else { panic("Cannot iterate !") } return c; } </code></pre> <p>With my initial example rewritten using it <a href="http://play.golang.org/p/lRmXX19tb9" rel="nofollow noreferrer">on the playground</a>.</p> <p>Thanks a lot to <a href="https://stackoverflow.com/users/1065241/jnml">jnml</a> and <a href="https://stackoverflow.com/users/694331/anisus">ANisus</a> for helping out !</p>
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