[golang syntax] be careful with the copy of slices

The properties of slices

stay go In a slice of

When operating on different slices based on the same array , In essence, it operates in the same array space

If we are copying slices

Take the following statement for granted

var nums = []int{1, 2, 3}
copy :=nums

It may lead to bug Appearance

Let's take a look at this example

We had hoped for a copy copy Operate without changing nums Value

For this purpose, we have created a new variable copy

However, the result is

The right thing to do is to use copy function

about copy Use of functions

We need to pay attention to the length of the parameter

If we use this copy

I thought I had finished the copy operation

But in fact

give the result as follows

because co When declared, the default initialization is nil

because copy Characteristics of functions ,copy The operation will not be co Expand capacity

At the completion of the copy After the operation, it will still be nil

So if we think we have finished copy If the operation directly uses the slice, an exception will occur
For example, complete the exchange operation
co[1], co[2] = co[2], co[1]

Will prompt for subscript out of bounds

panic: runtime error: index out of range [1] with length 0

The correct way is to initialize it into slices of equal length

So we can get the right result