The only alternatives that I see would each introduce an extra call to Add,
like the below. I'm not sure if this is much less "clunky", but it at least
avoids the reassignment to s.
func collectStringsetMap(m map[string]*stringset.Set, key string, value
...string) *stringset.Set {
if s, ok := m[key]; ok {
s.Add(value...)
return s
}
newset := stringset.New()
m[key] = &newset
newset.Add(value...)
return &newset
}
> Why can't I just use &(stringset.New()) ?
I'm unsure, but it might have something to do with Go being explicit and
the language designers wanting to make the stack allocation and transfer to
the heap explicit... or it might make Go's escape analysis feasible.
That said, you wouldn't have to worry about it if the library authors chose
to return a pointer, but in that case the caller would be forced to accept
a heap allocation on every stringset.New(). Returning a value has its
merits here.
On Tue, Sep 13, 2022, 4:44 PM 'Aaron Spangler' via golang-nuts <
golang-nuts@googlegroups.com> wrote:
> I seem to be regularly working with maps of stringsets and I have
> found myself writing the same pattern over and over and I ended up
> having my own utility function. More importantly the syntax seems
> clunky when a key doesn't exist in the map. Is there a better way (go
> idiomatically way) to write this?
>
> import "google3/third_party/golang/stringset/stringset"
>
> var urlMap = make(map[string]*stringset.Set)
>
> func collectStringsetMap(m map[string]*stringset.Set, key string,
> value ...string) *stringset.Set {
> s, ok := m[key]
> if !ok {
> newset := stringset.New() // Why can't I just use &(stringset.New()) ?
> s = &newset
> m[key] = s
> }
> s.Add(value...)
> return s
> }
>
> If there is a way to clean up the code, let me know.
>
> Also why can map's just take a default function to construct items
> that are not yet present?
> Something like:
>
> var urlMap = make(map[string]*stringset.Set, ...func =
> defaultStringsetConstructor...)
>
> func defaultStringsetConstructor(key string) *stringset.Set {
> n := stringset.New()
> return &n
> }
>
> Or perhaps some trickery in the map lookup?
>
> s, ok := m[key, defaultStringsetConstructor]
>
> At the end of the day you want the map to save any new items that were
> not already in the map, but I don't see any less clunky ways of doing
> this. (What am I missing?)
>
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> .
>
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