---
title: Use append to concatenate slices
description: Datadog, the leading service for cloud-scale monitoring.
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  Docs > Datadog Security > Code Security > Static Code Analysis (SAST) > SAST
  Rules > Use append to concatenate slices
---

# Use append to concatenate slices

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## Metadata{% #metadata %}

**ID:** `go-best-practices/concatenate-slices`

**Language:** Go

**Severity:** Info

**Category:** Best Practices

## Description{% #description %}

Programmers should avoid writing `for i := range y { x = append(x, y[i]) }` and use `x = append(x, y...)` instead.

Here are a few reasons why:

1. **Simplicity and readability**: The `x = append(x, y...)` expression is more concise and clearer in its intent. It directly appends all elements of `y` to `x` without the need for an explicit loop with index access. It is easier to read and understand for other developers.
1. **Performance**: Using the `x = append(x, y...)` syntax is generally faster and more efficient than iterating over each element of `y` using a `for` loop. The implicit use of variadic arguments in `append` reduces memory allocations and improves performance.
1. **Avoiding index access**: By using `x = append(x, y...)`, you eliminate the need for manual index access `y[i]` and let the built-in `append` function handle the internal implementation efficiently.
1. **Consistency**: Using `x = append(x, y...)` for concatenation is consistent with other idiomatic Go code. It is a widely accepted practice and is commonly used in the Go community.

By adopting the `x = append(x, y...)` approach, programmers can simplify their code, improve performance, and adhere to Go's idiomatic style. It enhances code readability, reduces the chance of typographical errors, and promotes efficient slicing and concatenation.

## Non-Compliant Code Examples{% #non-compliant-code-examples %}

```go
func main() {
    for i := range y {
        x = append(x, y[i])
    }
}
```

## Compliant Code Examples{% #compliant-code-examples %}

```go
func main() {
    x = append(x, y...)

    for _, e := range y {
        x = append(x, e)
    }
}
```
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