[SR-9918] FileHandle should conform to TextOutputStream

[sindresorhus]

Previous ID	SR-9918
Radar	rdar://problem/48032239
Original Reporter	@sindresorhus
Type	New Feature

Additional Detail from JIRA

Votes	0
Component/s	Foundation
Labels	New Feature
Assignee	None
Priority	Medium

md5: 1fba25807ce87df0c8054a24e5f11a3f

Issue Description:

That would make it easier to work with stdout, stderr, and other file handles. For example, using stderr with `print()` [1].

Currently, every project has to include this extension:

extension FileHandle: TextOutputStream {
    public func write(_ string: String) {
        write(string.data(using: .utf8)!)
    }
}

And then it can be used like this:

var standardError = FileHandle.standardError
print("foo", to: &standardError)

Relevant Stack Overflow question: https://stackoverflow.com/questions/24041554/how-can-i-output-to-stderr-with-swift

[1]: https://forums.swift.org/t/rework-print-by-adding-observable-standardoutput-and-standarderror-streams-to-standard-library/7775/3

[belkadan]

cc @millenomi, @milseman

[millenomi]

I like it, and I'll see what timeframe can have this if we do it. But as with all requests that add API surface, we can take feedback, but promise nothing.

[milseman]

SGTM. Also, it seems kinda weird that there's no way to access stderr in the standard library, and no way to name stdout/stderr.