Faulty prealloc

[cbndr]

I currently work in a team and we had a code issue a few times that made it beyond code review.
It is pre-allocating a slice with size instead of cap, then use append on it. Example

ar := make([]int, 10)
for i:=0; i<10; i++ {
  ar = append(ar, i)
  }

The correct pre-alloc would be ar := make([]int, 0, 10). Because of the missing 0,, the faulty code produces an array of size 20.

Would it be possible to add a check for this into your linter? I could not find any linter that has this check.

[alexkohler]

Hi, thanks for reaching out. At first glance, it looks like it might be possible to add some sort of check for these types of errors. I'll try to take a closer look when I get a moment.

[cbndr]

Thank you very much. I believe this mistake is quite common, especially due to the confusing pre-allocation of arrays vs maps in Golang. In arrays, the extra ,0 is needed to specify capacity, but not in maps.

[bunyk]

I recently found out that there is a linter for that: https://github.com/ashanbrown/makezero

That also has "Consider whether this should be part of prealloc itself." in TODO.