CA1826: Use property instead of Linq Enumerable method

Property	Value
Rule ID	CA1826
Title	Use property instead of Linq Enumerable method
Category	Performance
Fix is breaking or non-breaking	Non-breaking
Enabled by default in .NET 8	As suggestion

Cause

The Enumerable LINQ method was used on a type that supports an equivalent, more efficient property.

Rule description

This rule flags the Enumerable LINQ method calls on collections of types that have equivalent but more efficient properties to fetch the same data.

This rule analyzes collection types that implement IReadOnlyList<T> but not IList<T>.

This rule flags calls to the following methods on these collection types:

• System.Linq.Enumerable.Count
• System.Linq.Enumerable.First
• System.Linq.Enumerable.FirstOrDefault
• System.Linq.Enumerable.Last
• System.Linq.Enumerable.LastOrDefault

The analyzed collection types and methods may be extended in the future to cover more cases.

How to fix violations

To fix a violation, replace the Enumerable method call with property access. For example, the following two code snippets show a violation of the rule and how to fix it:

using System;
using System.Collections.Generic;
using System.Linq;

class C
{
    public void M(IReadOnlyList<string> list)
    {
        Console.Write(list.First());
        Console.Write(list.Last());
        Console.Write(list.Count());
    }
}

using System;
using System.Collections.Generic;

class C
{
    public void M(IReadOnlyList<string> list)
    {
        Console.Write(list[0]);
        Console.Write(list[list.Count - 1]);
        Console.Write(list.Count);
    }
}

Tip

A code fix is available for this rule in Visual Studio. To use it, position the cursor on the violation and press Ctrl+. (period). Choose Use indexer from the list of options that's presented.

When to suppress warnings

It's safe to suppress a violation of this rule if you're not concerned about the performance impact from specific Enumerable method calls.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA1826
// The code that's violating the rule is on this line.
#pragma warning restore CA1826

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA1826.severity = none

For more information, see How to suppress code analysis warnings.

Configure code to analyze

Use the following option to configure which parts of your codebase to run this rule on.

• Exclude FirstOrDefault and LastOrDefault methods

Exclude FirstOrDefault and LastOrDefault methods

You can configure this rule to exclude the Enumerable.FirstOrDefault and Enumerable.LastOrDefault methods from analysis. You might consider excluding these methods if readability is a concern, since the code you'd write to replace them is not easily readable. To exclude these methods, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CA1826.exclude_ordefault_methods = true

Related rules

• CA1827: Do not use Count/LongCount when Any can be used
• CA1828: Do not use CountAsync/LongCountAsync when AnyAsync can be used
• CA1829: Use Length/Count property instead of Enumerable.Count method

See also

• Performance rules