Interview Question: What is the difference between new() and make() in Golang?

Key Takeaways

• new() allocates memory and returns a pointer to zeroed memory (e.g., *int, *struct).
• make() initializes slices, maps, or channels and returns a ready-to-use value (not a pointer).
• Use new() for basic types (int, bool) or structs when you need a pointer.
• Use make() for slices, maps, or channels to avoid runtime errors like nil pointers.
• Both functions handle memory automatically—no manual cleanup is required.

Why Understanding new() and make() Matters in Go

In Go, memory management is handled differently compared to languages like C or Java. Misusing new() or make() can lead to runtime errors such as nil pointer dereferences or uninitialized data structures. Knowing the difference between these two functions is a common topic in software engineering interviews.

This guide will explain everything you need to know about new() and make() in Go, including their differences, use cases, and common mistakes to avoid.

What Does new() Do?

The new() function in Go allocates memory for a given type and returns a pointer to it. The allocated memory is initialized to the type’s zero value (e.g., 0 for integers, "" for strings, false for booleans).

Syntax

pointer := new(Type) // Returns *Type

Example

// Allocating a pointer to an int
numPtr := new(int)
fmt.Println(*numPtr) // Output: 0 (zero value of int)

// Allocating a pointer to a struct
type Person struct { Name string; Age int }
personPtr := new(Person)
fmt.Println(personPtr) // Output: &{ 0 }

When to Use new()

• You need a pointer to modify a value across functions.
• Working with basic types (e.g., int, string) or structs.

What Does make() Do?

The make() function in Go is used to initialize slices, maps, and channels so they are ready to use. Unlike new(), make() returns the actual value (not a pointer).

Syntax

slice := make([]Type, length, capacity)  
m := make(map[KeyType]ValueType)  
ch := make(chan Type)

Example

// Slice with length 3
names := make([]string, 3)
names[0] = "Alice" // Works (initialized)
fmt.Println(names) // Output: [Alice  ]

// Map
scores := make(map[string]int)
scores["Bob"] = 85 // No error

When to Use make()

• Creating slices, maps, or channels.
• Avoiding runtime errors like “nil map” or “slice out of bounds”.

new() vs make(): Key Differences

Here’s a table summarizing the key differences between new() and make():

Memory Management

Go simplifies memory management by handling it automatically:

• Both new() and make() allocate memory on the heap.
• Go’s garbage collector automatically frees memory when it’s no longer used.
• You don’t need to manually delete pointers or values.

Conclusion

Understanding the differences between new() and make() is essential for writing effective Go code. Using these functions correctly will help you allocate memory properly, initialize data structures, and create efficient, idiomatic Go programs. With this knowledge, you will be well-prepared for your software engineering interview.