What is the difference between := and =?

Question

Accepted Answer

**:=** — short variable declaration: creates and assigns. **=** — assignment: updates existing.

Short declarations are the idiomatic way to introduce variables in Go functions. Type is inferred. At least one new variable required.

```go
func main() {
    x := 42       // declares x
    y, z := 1, 2  // declares y, z
    x, w := 3, 4  // OK: w is new
}
```

Assignment updates existing variables.

```go
var a, b int
a, b = 1, 2  // assignment
a, b = b, a  // swap
```

**When to use:**
- **:=** — introducing new variables.
- **=** — updating existing.

**Common mistakes:**
- Shadowing in nested blocks.
- `:=` when all variables exist.
- `:=` at package level.
- Shadowing in `for` loops.

Go: What is the difference between := and =?