ArrayOrArrayReturningMethodFollowedByToArray

Diagnostic Rule Overview

Field	Value
ID	SHIMMER1012
Analyzer title	An array creation expression or array-returning method should not be followed by .ToArray()
Analyzer message	.ToArray() is redundant
Code fix title	Remove redundant .ToArray()
Default severity	Warning
Minimum framework/language version	N/A
Category	ShimmeringUsage
Link to code	ArrayOrArrayReturningMethodFollowedByToArrayAnalyzer.cs
Code fix exists?	Yes

Detailed Explanation

Calling .ToArray() on an existing array is redundant and wastes memory because .ToArray() will always create/allocate a new array.

Examples

Flagged code:

using System.Linq;

namespace Tests;
class Test
{
    void Do()
    {
        var array = "a b".Split(' ').ToArray();
    }
}

Fixed code:

using System.Linq;

namespace Tests;
class Test
{
    void Do()
    {
        var array = "a b".Split(' ');
    }
}

Justification of the Severity

While this is not a bug, this will slow down your code and increase memory usage with no benefits. As a reminder, calling .ToArray() on an existing array is not a no-op but rather creates and allocates a new array, so it has costs but not benefits.

Related Rules

• SHIMMER1010: .ToList().ForEach() causes unnecessary memory allocation
• SHIMMER1011: Unnecessary materialization to array/list in LINQ chain

Inspiration

This was inspired by @Treit's blog post https://mtreit.com/programming,/.net/2024/07/30/ToList.html. The same material was also covered in this YouTube video.