Object and Collection Initializers

Microsoft Docs / Object Initializers

Recommendation

Both object and collection initializers should be used, regardless of how many elements are being set.

Use:

Cat cat = new Cat
{
    Age = 10,
    Name = "Fluffy"
};

List<Cat> cats = new List<Cat>
{
    new Cat{ Name = "Sylvester", Age=8 },
    new Cat{ Name = "Whiskers", Age=2 },
    new Cat{ Name = "Sasha", Age=14 }
};

Not

Cat cat = new Cat();
cat.Age = 10;
cat.Name = "Fluffy";

List<Cat> cats = new List<Cat>();
cats.Add(new Cat{ Name = "Sylvester", Age=8 });
cats.Add(new Cat{ Name = "Whiskers", Age=2 };
cats.Add(new Cat{ Name = "Sasha", Age=14 };

Justification

Both the Roslyn and .Net Core runtime teams agree that object and collection initializers should be used.

Arguments

✔ Prevents objects and collections from being accessed before all necessary elements added / set.

✔ Helps to ensure lines aren’t misplaced during refactoring.

✔ Eliminates repetitive identifier usage (e.g. cat. and cats.Add).

❌ 2 Braces-only lines must always be added, even for individual elements.

❌ Introduces indentation for code blocks.

Performance

Identical IL is generated when using either object or collection initializers.

Benchmark code

Benchmark IL

Exceptions

Analyzers

Discussion

GitHub Discussion