What characteristic properties should keys in a map data structure have?

In Go, keys in a map must be of a comparable type, meaning they can be used with comparison operators == and !=. This is necessary for the map to efficiently search and compare keys.

Types that can be used as keys:

• Basic types: strings, numbers, boolean values.
• Pointers.
• Structs, if all their fields are comparable.

Types that cannot be used as keys:

• Slices, maps, functions, as they are not comparable.

Example:

m := make(map[string]int)
m["key"] = 42

Here, the key is a string, which is valid.