proposal: strings: implement Include function.

[dennypenta]

What version of Go are you using (go version)?

go version go1.10.3 darwin/amd64

Feature request.
Implement strings.Includes([]string, string) bool and same thing for other types.
At least once a week we need to check that slice of strings includes another string.
It's common code that we have to implement in every project and every package.

[mvdan]

A couple of observations:

• This should wait until a decision is made on generics. If the language ends up with generics, this function should work for all element types.
• This is an extra API to avoid a four-line function. I'm not sure if it warrants being in the standard library. In comparison, most other APIs in the strings package are either more complex or fairly optimized.

[networkimprov]

We have this for sorted arrays: https://golang.org/pkg/sort/#SearchStrings
That doesn't mention case-folding: https://golang.org/pkg/strings/#EqualFold
Is that an oversight?

A strings.Includes(slice, str) could use EqualFold() or equivalent. Might be more complex that way ;-)

The proposal could be directed instead to https://godoc.org/golang.org/x/text/search

It appears evident that a decision was already made to implement generics somehow, but it will be a couple years before anything lands!

[rsc]

At least once a week we need to check that slice of strings includes another string.
It's common code that we have to implement in every project and every package.

Can't you write a library and use it from those projects?

Also note that if the slice is large then that's not the best signature - better to use a map[string]bool instead of a []string.

In any event, this should be held for generics. This is an obvious thing we'd write in a 'slices' packages. (It's the canonical example of generic code, dating back to CLU.)