Use collection expression for stackalloc (IDE0302)

Article
2025-04-22

Property	Value
Rule ID	IDE0302
Title	Use collection expression for stackalloc
Category	Style
Subcategory	Language rules (expression-level preferences)
Applicable languages	C# 12+
Options	`dotnet_style_prefer_collection_expression`

Overview

This rule is similar to Use collection expression for array (IDE0300) except it looks for stackalloc instead of arrays. Like IDE0300, it offers to convert the code to use a collection expression. For example, stackalloc int[] { ... } and stackalloc [] { ... } are simplified to [...].

Note

This rule is only available in .NET 8 and later versions where the values can be preserved on the stack.

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, `List<int> list = new List<int>() { 1, 2 };`.
	`when_types_loosely_match`*	Prefer to use collection expressions even when types match loosely, for example, `IEnumerable<int> list = new List<int>() { 1, 2 };`. 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	`when_types_loosely_match`*

*When this option is used, the code fix might change the semantics of your code.

The when_types_loosely_match value for does not apply to this rule IDE0302, but is listed here for completeness of the dotnet_style_prefer_collection_expression option (which is shared by multiple rules). The default value is effectively true.

Example

// Code with violations.
ReadOnlySpan<int> x = stackalloc int[] { 1, 2, 3 };

// Fixed code.
ReadOnlySpan<int> x = [1, 2, 3];

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 IDE0302
// The code that's violating the rule is on this line.
#pragma warning restore IDE0302

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

[*.{cs,vb}]
dotnet_diagnostic.IDE0302.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.

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