## Why is this an issue?

Most developers expect property access to be as efficient as field access. However, if a property returns a copy of an array or collection, it will be much slower than a simple field access, contrary to the caller’s likely expectations. Therefore, such properties should be refactored into methods so that callers are not surprised by the unexpectedly poor performance.

This rule tracks calls to the following methods inside properties:

- Enumerable.ToList
- Enumerable.ToArray
- Array.Clone

## How to fix it

### Code examples

#### Noncompliant code example

    private List<string> foo = new List<string> { "a", "b", "c" };
    private string[] bar = new string[] { "a", "b", "c" };

    public IEnumerable<string> Foo => foo.ToList(); // Noncompliant: collection foo is copied

    public IEnumerable<string> Bar => (string[])bar.Clone(); // Noncompliant: array bar is copied

#### Compliant solution

    private List<string> foo = new List<string> { "a", "b", "c" };
    private string[] bar = new string[] { "a", "b", "c" };

    public IEnumerable<string> GetFoo() => foo.ToList();

    public IEnumerable<string> GetBar() => (string[])bar.Clone();

## Resources

### Documentation

- Properties (C# Programming Guide)
- Fields (C# Programming Guide)
- Collections (C#)
- Enumerable.ToList
- Enumerable.ToArray
- Array.Clone