proposal: io: SeekStart, SeekCurrent, SeekEnd should have explicit types

[rsc]

The os package defines

const (
	SEEK_SET int = 0 // seek relative to the origin of the file
	SEEK_CUR int = 1 // seek relative to the current offset
	SEEK_END int = 2 // seek relative to the end
)

For #6885, these were deprecated and recreated in package io. This change does make sense, since io defines the Seeker interface. However, the recreation in package io in golang.org/cl/19862 (acefcb7) is less safe to use than the original in package os, because the explicit int types were dropped:

// Seek whence values.
const (
	SeekStart   = 0 // seek relative to the origin of the file
	SeekCurrent = 1 // seek relative to the current offset
	SeekEnd     = 2 // seek relative to the end
)

This is a mistake and does not compile:

f.Seek(os.SEEK_END, 0)

This is a mistake but DOES compile:

f.Seek(io.SeekEnd, 0)

(It seeks to byte 2 of the file.)

It would be nice if we can fix this at some point by making those constants have type int. Maybe Go 2.

[bradfitz]

I'd prefer to delete all these constants for Go 2. io.Seeker is three interfaces in one, with a C interface. I've seen so many fake & lying implementations of Seeker that only implement 1 or sometimes 2 of the methods, and sometimes partially.

[ianlancetaylor]

@griesemer and I think that @bradfitz has a good point: if we change things for Go 2, let's consider changing the Seek method to not take a whence argument at all.

[ianlancetaylor]

Moved @bradfitz 's suggestion to new issue #25854.

[ianlancetaylor]

Closing in favor of #25854.