proposal: strings: add new functions to deprecate strings.{Trim/TrimRight/TrimLeft} to avoid mistakes

[hitzhangjie]

Hi, could we add new methods to solve the problem of cutset type in Strings.{Trim/TrimRight/TrimLeft}.

Apparently, many gohpers misunderstood the this cutset type, and it cauese some bugs. And, there're several proposals for solving the cutset type problem:

• cmd/vet: report strings.Trim/TrimLeft/TrimRight with duplicate runes in cutset #46533
• proposal: cmd/vet warns when the cutset of strings.{Trim,TrimLeft,TrimRight} is not in order #47822

I read through this proposals and see the conclusion is no change will be made.

This cutset problem affects many developers:

• if we have known the problem already, we may not make the same mistake again.
• but if we doesn't know it in advance, we may likely make the mistake.

In python, str.{strip/rstrip/lstrip}('cutset') method works the same as in go strings.{Trim/TrimRight/TrimLeft}(s, "cutset"). Maybe this signature is ok.

If we:

• add new methods strings.{TrimCutset\TrimRightCutset\TrimLeftCutset}, and add //Deprecated and go:linkname on strings.{Trim/TrimRight/TrimLeft}, we may make this clearer
• or add new methods strings.{TrimCutset\TrimRightCutset\TrimLeftCutset}, and declare the cutset as []rune, and use this methods to reimplement strings.{Trim/TrimRight/TrimLeft}

[martisch]

I dont see how using []rune will avoid the duplicate characters in cutset issues as the user now may as well define duplicate elements in []rune. In addition []rune has the downside of not being a 1 to 1 replacement of the old function signature and has larger storage requirements and is not constant.

I dont think Strip conveys a meaning that it is a cutset more or less then Trim so I dont think just advising to use Strip instead of Trim makes developers more or less likely to mistake the function as not using a cutset.

[hitzhangjie]

@martisch I edit the issue again to focus on 1 suggestion. Thanks.

[ianlancetaylor]

Presumably if we do something in the strings package we would also it in the bytes package.