Is there a foreach loop in Go?

Is there a foreach construct in the Go language? Can I iterate over a slice or array using a for ?

---

http://golang.org/doc/go_spec.html#For_statements

A "for" statement with a "range" clause iterates through all entries of an array, slice, string or map, or values received on a channel. For each entry it assigns iteration values to corresponding iteration variables and then executes the block.

As an example:

for index, element := range someSlice {
    // index is the index where we are
    // element is the element from someSlice for where we are
}

If you don't care about the index, you can use _ :

for _, element := range someSlice {
    // element is the element from someSlice for where we are
}

The underscore, _ , is the blank identifier, an anonymous placeholder.

---

Iterate over array or slice :

// index and value
for i, v := range slice {}

// index only
for i := range slice {}

// value only
for _, v := range slice {}

Iterate over a map :

// key and value
for key, value := range theMap {}

// key only
for key := range theMap {}

// value only
for _, value := range theMap {}

Iterate over a channel :

for v := range theChan {}

Iterating over a channel is equivalent to receiving from a channel until it is closed:

for {
    v, ok := <-theChan
    if !ok {
        break
    }
}

---

The following example shows how to use the range operator in a for loop to implement a foreach loop.

func PrintXml (out io.Writer, value interface{}) error {
    var data []byte
    var err error

    for _, action := range []func() {
        func () { data, err = xml.MarshalIndent(value, "", "  ") },
        func () { _, err = out.Write([]byte(xml.Header)) },
        func () { _, err = out.Write(data) },
        func () { _, err = out.Write([]byte("n")) }} {
        action();
        if err != nil {
            return err
        }
    }
    return nil;
}

The example iterates over an array of functions to unify the error handling for the functions. A complete example is at Google´s playground.

PS: it shows also that hanging braces are a bad idea for the readability of code. Hint: the for condition ends just before the action() call. Obvious, isn't it?

链接地址: http://www.djcxy.com/p/59142.html

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