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CA1827: Do not use Count/LongCount when Any can be used

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Value
Rule ID CA1827
Category Performance
Fix is breaking or non-breaking Non-breaking

Cause

The Count or LongCount method was used where the Any method would be more efficient.

Rule description

This rule flags the Count and LongCount LINQ method calls used to check if the collection has at least one element. These method calls require enumerating the entire collection to compute the count. The same check is faster with the Any method as it avoids enumerating the collection.

How to fix violations

To fix a violation, replace the Count or LongCount method call with the Any method. For example, the following two code snippets show a violation of the rule and how to fix it:

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

class C
{
    public string M1(IEnumerable<string> list)
        => list.Count() != 0 ? "Not empty" : "Empty";

    public string M2(IEnumerable<string> list)
        => list.LongCount() > 0 ? "Not empty" : "Empty";
}

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

class C
{
    public string M1(IEnumerable<string> list)
        => list.Any() ? "Not empty" : "Empty";

    public string M2(IEnumerable<string> list)
        => list.Any() ? "Not empty" : "Empty";
}

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 Do not use Count() or LongCount() when Any() can be used from the list of options that's presented.

Code fix for CA1827 - Do not use Count() or LongCount() when Any() can be used

When to suppress warnings

It's safe to suppress a violation of this rule if you're not concerned about the performance impact from unnecessary collection enumeration to compute the count.

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 CA1827
// The code that's violating the rule is on this line.
#pragma warning restore CA1827

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

[*.{cs,vb}]
dotnet_diagnostic.CA1827.severity = none

To disable this entire category of rules, set the severity for the category to none in the configuration file.

[*.{cs,vb}]
dotnet_analyzer_diagnostic.category-Performance.severity = none

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

See also