Map in Go

Master Go maps: creation, access, mutation, traversal, comparison, and cloning (shallow, JSON deep, recursive deep).

Introduction to Maps

Maps are Go’s key-value collections. They store key-value pairs and support lookup, add, update, and delete by key.

1. What is a Map?

Key-value data structure.

Creating Maps

Create maps with a composite literal or with make(). An uninitialized map is nil and cannot be written to.

1. Map Literal

Most common and readable.

2. make() for Maps

Create an empty map, then add keys.

Accessing & Updating

Access by key with m[key]. Use the two-value form to check whether the key exists. Update by assigning to m[key].

1. Access by Key

Use m[key]. Check presence with second value.

2. Dynamic Key (Variable)

Keys are expressions; use a variable for runtime keys.

3. Updating Values

Assign to m[key] to change the value.

Adding & Deleting Keys

Add a key by assigning to m[key]. Remove a key with delete(m, key).

1. Adding Keys

Assign to a new key.

2. Deleting Keys

Use delete(m, key).

Traversing Maps

Use for range over the map. Iteration order is not guaranteed. Range over keys only, or keys and values together.

1. Range over Keys

for k := range m.

2. Range over Key-Value Pairs

for k, v := range m.

Comparing Maps

Maps are compared by reference. To compare by contents, use reflect.DeepEqual or a custom loop.

1. Reference Comparison

a == b is invalid in Go; if it were allowed, it would be false even when contents are the same.

2. Value Comparison with reflect.DeepEqual

Deep equality of key-value pairs.

Cloning Maps

Shallow clone: copy key-value pairs into a new map. Deep clone: use JSON marshal/unmarshal or a recursive function that copies nested maps and slices.

1. Shallow Clone

Copy keys and values into a new map.

2. Deep Clone (JSON)

Using JSON marshal/unmarshal.

3. Deep Clone (Recursive Function)

Flexible deep clone: primitives copied by value; maps and slices recursively cloned at every nested level.