Go Maps: `make` vs. Map Literal – When Should I Use Which?

Clarifying the Differences Between Map Initialization with and without "make"

When working with Go maps, there are two primary ways to initialize them: using a map literal or invoking the "make" function. Understanding the subtle nuances between these methods is crucial for optimizing code performance.

Map Literals vs. "make"

The second approach, using "make(map[string]int)", consistently creates an empty map. However, the first method, "var m = map[string]int{}", represents a map literal. This technique is reserved for initializing maps with non-empty values.

Example:

m := map[bool]string{false: "FALSE", true: "TRUE"}

Map Literals Without Initial Values

Generalizing your example, "m := map[T]U{}", produces a map literal with no initial key-value pairs. This is functionally identical to "m := make(map[T]U)".

Performance Considerations

When initializing an empty map, there is virtually no performance difference between using a map literal or "make". Both approaches generate an empty map and occupy the same amount of memory.

Specifying Initial Capacity

The true advantage of using "make" lies in its ability to specify an initial capacity for a map. By default, maps are initialized with a growth factor that doubles their size each time their capacity is exceeded. However, using "make" allows you to predetermine the map's size.

Example:

m := make(map[T]U, 50)

The above code creates a map with sufficient space to accommodate up to 50 elements. This approach can help minimize future memory allocations if you anticipate the map's size increasing significantly.

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