Are Maps Passed By Reference Golang

Go Programming

In Go, maps are passed by reference. This means that when you pass a map as an argument to a function or method, you are actually passing a reference to the original map rather than making a copy of the map. This behavior can have important implications in terms of how changes to the map are handled within the context of the function or method.

As a developer who has worked extensively with Go, I have found the concept of passing maps by reference to be both powerful and at times challenging to work with. Let’s delve deeper into this topic and explore the implications of passing maps by reference in Go.

Understanding Pass by Reference

When a map is passed by reference in Go, any modifications made to the map within the function or method will directly affect the original map outside the function or method. This can be advantageous when working with large data sets, as it avoids the overhead of copying the entire map. However, it also requires careful consideration of potential side effects and concurrent access to the map.

For example, consider the following function:

func modifyMap(m map[string]int) {
m["newKey"] = 100

If we were to call this function with a map, the original map would be modified:

myMap := make(map[string]int)

After calling modifyMap, the original myMap would now have the key “newKey” with the value 100. This illustrates the concept of passing maps by reference in Go.

Implications and Considerations

While the ability to pass maps by reference can be efficient, it also introduces potential complexities. Concurrent access to the same map from multiple goroutines, for example, requires careful synchronization to avoid data races and inconsistent state. Additionally, developers must be mindful of unintended modifications to the original map outside the scope of the function or method.

Consider the following scenario:

func modifyMapConcurrently(m map[string]int) {
// perform concurrent modifications to the map

When working with concurrent modifications to a map passed by reference, it is crucial to coordinate access using Go’s built-in synchronization primitives such as channels or the sync package to prevent data corruption and ensure consistency.

Best Practices and Recommendations

When dealing with maps in Go, it is important to establish clear guidelines for handling map references, especially in the context of concurrent access. Carefully document any functions or methods that modify a map passed by reference, and consider utilizing Go’s concurrency patterns to maintain data integrity.

Additionally, consider leveraging immutable data structures or using copy-on-write techniques when the original map should not be modified. Immutable maps can provide a level of safety and predictability in concurrent scenarios.


Passing maps by reference in Go offers performance benefits and can streamline the manipulation of map data within functions and methods. However, it also introduces considerations for concurrent access and potential side effects. By understanding the implications of passing maps by reference and following best practices for managing map references, developers can harness the power of Go’s map behavior while mitigating potential pitfalls.