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+# Range Clauses
+
+Spec: http://golang.org/doc/go_spec.html#For_statements
+
+## Summary
+
+A range clause provides a way to iterate over a array, slice, string, map, or channel.
+
+## Example
+
+```
+for k, v := range myMap {
+ log.Printf("key=%v, value=%v", k, v)
+}
+
+for v := range myChannel {
+ log.Printf("value=%v", v)
+}
+
+for i, v := range myArray {
+ log.Printf("array value at [%d]=%v", i, v)
+}
+```
+
+## Reference
+
+If only one value is used on the left of a range expression, it is the 1st value in this table.
+
+| Range expression | 1st value | 2nd value (optional) | notes |
+|:-----------------|:----------|:---------------------|:------|
+| array or slice a ` [n]E `, ` *[n]E `, or ` []E ` | index ` i int ` | ` a[i] ` E |
+| string s string type | index ` i int ` | rune ` int ` | range iterates over Unicode code points, not bytes |
+| map m ` map[K]V ` | key ` k K ` | value ` m[k] ` V |
+| channel c chan E | element ` e E ` | _none_ |
+
+## Gotchas
+
+When iterating over a slice or map of values, one might try this:
+
+```
+items := make([]map[int]int, 10)
+for _, item := range items {
+ item = make(map[int]int, 1) // Oops! item is only a copy of the slice element.
+ item[1] = 2 // This 'item' will be lost on the next iteration.
+}
+```
+
+The ` make ` and assignment look like they might work, but the value property of ` range ` (stored here as ` item `) is a _copy_ of the value from ` items `, not a pointer to the value in ` items `. The following will work:
+
+```
+items := make([]map[int]int, 10)
+for i := range items {
+ items[i] = make(map[int]int, 1)
+ items[i][1] = 2
+}
+```
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