切片如何通过追加放大？ 容量是否总是增加一倍？

Question

When append a slice, the slice may be enlarged if necessary. Because the spec doesn't specify the algorithm, I am curious about it.

I try to find the append implementation in the Go source code, but can't find it.

Could anyone explain the specified algorithm for enlarging slice? Is the capacity always doubled? or Could anyone provide the source code position of append? I can check it myself.

Answer 1

The code responsible for growing slices in append can be found here.

So in the current implementation, the rules are:

1. If appending to the slice will increase its length by more than double, the new capacity is set to the new length.
2. Otherwise, double the capacity if the current length is less than 1024, or by 25% if it is larger. Repeat this step until the new capacity fits the desired length.

Presumably this isn't part of the specification so the heuristics can be changed in future if needed.