How to use range to modify elements in arrays/slices/maps and channels

When using golang programming, we often use the range keyword, which is used to traverse data structures such as arrays, slices, maps, and channels. However, during the traversal process, if we want to modify the traversed elements, we will encounter some problems. This article will explain how to use range to modify elements in arrays, slices, maps, and channels.

1. Modify array and slice elements

When traversing arrays and slices, the range keyword returns a copy of the element, not the element itself. Therefore, if we want to modify an element, we need to use the element's pointer. The following is a code example for modifying array and slice elements:

arr := [3]int{1, 2, 3}
for i := range arr {
  temp := &arr[i]
  *temp = *temp*2
}

slice := []int{1, 2, 3}
for i := range slice {
  temp := &slice[i]
  *temp = *temp*2
}

The temporary variable temp is used in the code to save the pointer of the element and modify the value of the element through the pointer.

2. Modify map elements

When traversing the map, the range keyword returns a copy of the key-value pair, not the element itself. So, if we want to modify an element, we need to use the key to access the element and modify its value. The following is a code example for modifying map elements:

oldMap := map[string]int{"a": 1, "b": 2, "c": 3}
newMap := make(map[string]int)
for k, v := range oldMap {
  newMap[k] = v*2
}

In the code, when traversing the map, keys are used to access elements and modify their values. Note that you do not need to use pointers when modifying the values ​​of elements in the map.

3. Modify the elements in the channel

When traversing the channel, the range keyword returns a copy of the element, not the element itself. Therefore, if we want to modify the elements in the channel, we need to use the channel's send operation to modify the value in the channel. The following is a code example for modifying elements in the channel:

ch := make(chan int, 3)
ch <- 1
ch <- 2
ch <- 3

for i := range ch {
  ch <- i*2
}

In the code, the send operation of the channel is used to modify the value of the element to twice its original value. It should be noted that when modifying elements in a channel, the send operation of the channel must be used to send the modified value to the channel.

Summary:

When using the range keyword to traverse arrays, slices, maps and channels, if we want to modify the traversed elements, we need to use the pointer of the element (array and slice), use key to access an element (map), or use a channel's send operation to modify an element's value (channel). It should be noted that when using range to modify elements, you must be careful not to cause problems such as infinite loops or race conditions in the loop.

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