Prefer make(..) for empty maps, and maps populated
programmatically. This makes map initialization visually
distinct from declaration, and it makes it easy to add size
hints later if available.
| Bad | Good |
|---|---|
var (
// m1 is safe to read and write;
// m2 will panic on writes.
m1 = map[T1]T2{}
m2 map[T1]T2
) |
var (
// m1 is safe to read and write;
// m2 will panic on writes.
m1 = make(map[T1]T2)
m2 map[T1]T2
) |
|
Declaration and initialization are visually similar. |
Declaration and initialization are visually distinct. |
Where possible, provide capacity hints when initializing
maps with make(). See
Specifying Map Capacity Hints
for more information.
On the other hand, if the map holds a fixed list of elements, use map literals to initialize the map.
| Bad | Good |
|---|---|
m := make(map[T1]T2, 3)
m[k1] = v1
m[k2] = v2
m[k3] = v3 |
m := map[T1]T2{
k1: v1,
k2: v2,
k3: v3,
} |
The basic rule of thumb is to use map literals when adding a fixed set of
elements at initialization time, otherwise use make (and specify a size hint
if available).