Why is this an issue?

Both the List.TrueForAll method and the IEnumerable.All method can be used to check if all list elements satisfy a given condition in a collection. However, List.TrueForAll can be faster than IEnumerable.All for List objects. The performance difference may be minor for small collections, but for large collections, it can be noticeable.

Applies to

• List
• Array
• ImmutableList
• ImmutableList.Builder

What is the potential impact?

We measured at least 4x improvement both in execution time. For more details see the Benchmarks section from the More info tab.

How to fix it

The TrueForAll method is defined on the collection class, and it has the same signature as the All extension method. The method can be replaced in place.

Code examples

Noncompliant code example

public bool AreAllEven(List<int> data) =>
    data.All(x => x % 2 == 0);

public bool AreAllEven(int[] data) =>
    data.All(x => x % 2 == 0);

Compliant solution

public bool AreAllEven(List<int> data) =>
    data.TrueForAll(x => x % 2 == 0);

public bool AreAllEven(int[] data) =>
    Array.TrueForAll(data, x => x % 2 == 0);

Resources

Documentation

• List<T>.TrueForAll(Predicate<T>)
• Array.TrueForAll<T>(T[], Predicate<T>)
• ImmutableList<T>.TrueForAll(Predicate<T>)
• ImmutableList<T>.Builder.TrueForAll(Predicate<T>)
• Enumerable.All<TSource>

Benchmarks

The results were generated by running the following snippet with BenchmarkDotNet:

private List<int> data;

[Params(10_000)]
public int N { get; set; }

[GlobalSetup]
public void Setup() =>
    data = Enumerable.Range(0, N).Select(x => 42).ToList();

[Benchmark]
public void TrueForAll()
{
    for (var i = 0; i < N; i++)
    {
        _ = data.TrueForAll(x => x == 42);  // List<T>.TrueForAll
    }
}

[Benchmark(Baseline = true)]
public void All()
{
    for (var i = 0; i < N; i++)
    {
        _ = data.All(x => x == 42);         // Enumerable.All<TSource>
    }
}

Hardware configuration:

BenchmarkDotNet=v0.13.5, OS=Windows 10 (10.0.19045.2846/22H2/2022Update)
12th Gen Intel Core i7-12800H, 1 CPU, 20 logical and 14 physical cores
.NET SDK=7.0.203
  [Host]               : .NET 7.0.5 (7.0.523.17405), X64 RyuJIT AVX2
  .NET 7.0             : .NET 7.0.5 (7.0.523.17405), X64 RyuJIT AVX2
  .NET Framework 4.6.2 : .NET Framework 4.8 (4.8.4614.0), X64 RyuJIT VectorSize=256