On Wed, 11 Apr 2018, Ian Lance Taylor wrote:
> On Wed, Apr 11, 2018 at 6:11 AM, Robert P. J. Day <[email protected]>
> wrote:
> >
> > total beginner question here, but the docs seem vague or
> > inconsistent on what should be a simple question -- what does it mean
> > to import a name that is a single .a file versus importing a directory
> > name from under GOROOT (in my case, on fedora, /usr/lib/golang).
> >
> > first, running on fedora 28 beta, go version 1.10.1, and i see the
> > directory structure /usr/lib/golang and, under that, the further
> > directory layout pkg/linux_amd64, which i assume is where go will
> > begin its search for packages i specify to import -- that directory
> > contains, at its top level:
> >
> > $ ls -F
> > archive/ debug/ html/ math/ plugin.a sync.a
> > bufio.a encoding/ html.a math.a reflect.a syscall.a
> > bytes.a encoding.a image/ mime/ regexp/ testing/
> > cmd/ errors.a image.a mime.a regexp.a testing.a
> > compress/ expvar.a index/ net/ runtime/ text/
> > container/ flag.a internal/ net.a runtime.a time.a
> > context.a fmt.a io/ os/ sort.a unicode/
> > crypto/ go/ io.a os.a strconv.a unicode.a
> > crypto.a hash/ log/ path/ strings.a vendor/
> > database/ hash.a log.a path.a sync/
> > $
> >
> > so far, so good.
> >
> > now, when i, for example:
> >
> > import "fmt"
> >
> > i assume that what is being imported is the package represented by
> > that single archive file, fmt.a, correct? that seems simple enough, as
> > there is no fmt/ directory, so my initial understanding is that an
> > import is meant to import the contents of a single ".a" go package
> > file.
> >
> > consider, next, an example where there is both an archive file and a
> > corresponding subdirectory, say "hash.a" and "hash/". if i simply did
> > this:
> >
> > import "hash"
> >
> > i'm *assuming* that would import the package corresponding to only the
> > archive file "hash.a", correct? if i wanted to import a hash
> > "subpackage" (say, hash/crc32.a), then the import would look like:
> >
> > import "hash/crc32"
> >
> > which would import *only* that hash-related package. (i realize this
> > all sounds trivial, it would just be nice if the docs came right out
> > and said it.)
> >
> > finally, what if there is no top-level .a file, and *only* a
> > subdirectory, such as for container/:
> >
> > $ tree container
> > container
> > ├── heap.a
> > ├── list.a
> > └── ring.a
> > $
> >
> > given that there is no top-level container.a file, would it even
> > make any sense to say:
> >
> > import "container"
> >
> > i realize this is all trivially trivial, but it would be nice if,
> > early in the docs, this was spelled out clearly and directly (unless,
> > of course, it is and i just haven't got to that section yet).
>
> The .a files under $GOROOT/pkg are most usefully thought of a cache
> of compiled code.
ah, that clarifies bunches.
> When you import "fmt", you are importing the package named "fmt" in
> $GOROOT/src. For any general non-relative import "a/b/c" the go
> tool will look in $GOROOT/src then in the src directory of each
> entry in $GOPATH. The package in one of those src directories is
> always what is being imported. The go tool may then decide to save
> some time by using the cached precompiled .a file in $GOROOT/pkg or
> $GOPATH/pkg. In future releases of Go, it is quite possible that
> $GOPATH/pkg, and maybe even $GOROOT/pkg, will go away entirely, to
> be replaced by $GOCACHE.
ah, it's all (i think) clear now. so, based on what i see under
${GOROOT}/src/hash, i could do any or all of the following:
import "hash"
import "hash/adler32"
import "hash/crc32"
import "hash/crc64"
import "hash/fnv"
which all represent distinct imports. however, it would make no sense
to:
import "container"
as there is no .go file immediately under that directory; rather, my
only options would be:
import "container/heap"
import "container/list"
import "container/ring"
as long as i'm getting that right, it all seems so simple now, once
it's explained. :-)
i might have a related question shortly after i read more. thank you
kindly.
rday
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