Use collection expression for Create()
(IDE0303)
Property | Value |
---|---|
Rule ID | IDE0303 |
Title | Use collection expression for Create |
Category | Style |
Subcategory | Language rules (expression-level preferences) |
Applicable languages | C# 12+ |
Options | dotnet_style_prefer_collection_expression |
Overview
This rule flags places where a Create()
method or a similar method that's designated as the collection construction method (using the CollectionBuilderAttribute attribute) is used to initialize a collection and offers to replace it with a collection expression ([...]
).
Create()
methods are common for the immutable collections, for example, ImmutableArray.Create(1, 2, 3)
.
Note
This rule requires more recent versions of the immutable APIs (for example, System.Collections.Immutable), which opt into the collection-expression pattern.
Options
Options specify the behavior that you want the rule to enforce. For information about configuring options, see Option format.
dotnet_style_prefer_collection_expression
Property | Value | Description |
---|---|---|
Option name | dotnet_style_prefer_collection_expression | |
Option values | true | when_types_exactly_match |
Prefer to use collection expressions only when types match exactly, for example, ImmutableArray<int> i = ImmutableArray.Create(1, 2, 3); . |
when_types_loosely_match (.NET 9 and later versions)* |
Prefer to use collection expressions even when types match loosely, for example, IEnumerable<int> i = ImmutableArray.Create(1, 2, 3); . The targeted type must match the type on the right-hand side or be one of the following types: IEnumerable<T>, ICollection<T>, IList<T>, IReadOnlyCollection<T>, IReadOnlyList<T>. |
|
false | never |
Disables the rule. | |
Default option value | true in .NET 8when_types_loosely_match in .NET 9 and later versions |
*The code fix when this option is used might change the semantics of your code.
Example
// Code with violations.
ImmutableArray<int> i = ImmutableArray.Create(1, 2, 3);
IEnumerable<int> j = ImmutableArray.Create(1, 2, 3);
// Fixed code.
ImmutableArray<int> i = [1, 2, 3];
IEnumerable<int> j = [1, 2, 3];
The following code snippet shows an example with a custom type that's annotated with CollectionBuilderAttribute.
public class Program
{
public static void Main()
{
// IDE0303 violation.
MyCollection<int> c = MyCollection.Create(1, 2, 3);
// IDE0303 fixed code.
MyCollection<int> c = [1, 2, 3];
}
}
static partial class MyCollection
{
public static MyCollection<T> Create<T>(System.ReadOnlySpan<T> values) => default;
public static MyCollection<T> Create<T>(T t1, T t2, T t3) => default;
}
[CollectionBuilder(typeof(MyCollection), "Create")]
class MyCollection<T> : IEnumerable<T>
{
public IEnumerator<T> GetEnumerator() => default;
IEnumerator IEnumerable.GetEnumerator() => default;
}
Suppress a warning
If you want to suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.
#pragma warning disable IDE0303
// The code that's violating the rule is on this line.
#pragma warning restore IDE0303
To disable the rule for a file, folder, or project, set its severity to none
in the configuration file.
[*.{cs,vb}]
dotnet_diagnostic.IDE0303.severity = none
To disable all of the code-style rules, set the severity for the category Style
to none
in the configuration file.
[*.{cs,vb}]
dotnet_analyzer_diagnostic.category-Style.severity = none
For more information, see How to suppress code analysis warnings.
See also
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