Closed as not planned
Description
Proposal Details
In the following code, is it possible to make generic deduction smarter?
Keys can be applied to most scenarios, but Keys2 can cover the underlying type scenarios. In the test case, Keys2 cannot deduce Slice by itself, so the complete type indication must be written.
// Keys creates an array of the map keys.
func Keys[K comparable, V any, Map ~map[K]V](in ...Map) []k {
size := 0
for i := range in {
size += len(in[i])
}
result := make([]k, 0, size)
for i := range in {
for k := range in[i] {
result = append(result, k)
}
}
return result
}
// Keys2 creates an array of the map keys.
func Keys2[K comparable, V any, Map ~map[K]V, Slice ~[]K](in ...Map) Slice {
size := 0
for i := range in {
size += len(in[i])
}
result := make(Slice, 0, size)
for i := range in {
for k := range in[i] {
result = append(result, k)
}
}
return result
}tests case
func TestKeys(t *testing.T) {
t.Parallel()
is := assert.New(t)
type myMap map[string]int
keys := Keys(myMap{"foo": 1, "bar": 2}, myMap{"baz": 3})
is.Equal(keys, []string{"foo", "bar", "baz"})
}
func TestKeys2(t *testing.T) {
t.Parallel()
is := assert.New(t)
type myMap map[string]int
type myStrings []string
r1 := Keys[string, int, myMap, myStrings](myMap{"foo": 1, "bar": 2})
is.IsType(r1, myStrings{}, "type preserved")
is.Equal(r1, myStrings{"foo", "bar"})
}