[API proposal] Collection expressions: IOperation support #70631
Description
Background and Motivation
Provide IOperation support for collection expressions.
Proposed API
namespace Microsoft.CodeAnalysis.Operations
{
/// <summary>
/// Represents a collection expression.
/// <para>
/// Current usage:
/// (1) C# collection expression.
/// </para>
/// </summary>
public interface ICollectionExpressionOperation : IOperation
{
/// <summary>
/// Method used to construct the collection.
/// <para>
/// If the collection type is an array, span, array interface, or type parameter, the method is null;
/// if the collection type has a [CollectionBuilder] attribute, the method is the builder method;
/// otherwise, the method is the collection type constructor.
/// </para>
/// </summary>
IMethodSymbol? ConstructMethod { get; }
/// <summary>
/// Collection expression elements.
/// <para>
/// If the element is an expression, the entry is converted to the target element type;
/// otherwise, the entry is an ISpreadOperation.
/// </para>
/// </summary>
ImmutableArray<IOperation> Elements { get; }
}
/// <summary>
/// Represents a collection expression spread element.
/// <para>
/// Current usage:
/// (1) C# spread element.
/// </para>
/// </summary>
public interface ISpreadOperation : IOperation
{
/// <summary>
/// Collection being spread.
/// </summary>
IOperation Operand { get; }
/// <summary>
/// Type of the collection iterator item.
/// </summary>
ITypeSymbol ItemType { get; }
/// <summary>
/// Conversion from the type of the iterator item to the target element type
/// of the containing collection expression.
/// </summary>
CommonConversion ItemConversion { get; }
}
}
namespace Microsoft.CodeAnalysis.CSharp
{
public readonly struct Conversion
{
// ...
public bool IsCollectionExpression { get; }
}
public static class CSharpExtensions
{
// ...
/// <summary>
/// Gets the underlying item <see cref="Conversion"/> information from this <see cref="ISpreadOperation"/>.
/// </summary>
public static Conversion GetSpreadItemConversion(this ISpreadOperation spread);
}
}Usage Examples
Span:
// Span<object> x = [1];
ICollectionExpressionOperation (1 elements, ConstructMethod: null) (OperationKind.CollectionExpression, Type: System.Span<System.Object>) (Syntax: '[1]')
Elements(1):
IConversionOperation (TryCast: False, Unchecked) (OperationKind.Conversion, Type: System.Object, IsImplicit) (Syntax: '1')
Conversion: CommonConversion (Exists: True, IsIdentity: False, IsNumeric: False, IsReference: False, IsUserDefined: False) (MethodSymbol: null)
Operand:
ILiteralOperation (OperationKind.Literal, Type: System.Int32, Constant: 1) (Syntax: '1')
Collection initializer type:
// List<object> x = [1];
ICollectionExpressionOperation (1 elements, ConstructMethod: System.Collections.Generic.List<System.Object>..ctor()) (OperationKind.CollectionExpression, Type: System.Collections.Generic.List<System.Object>) (Syntax: '[1]')
Elements(1):
IConversionOperation (TryCast: False, Unchecked) (OperationKind.Conversion, Type: System.Object, IsImplicit) (Syntax: '1')
Conversion: CommonConversion (Exists: True, IsIdentity: False, IsNumeric: False, IsReference: False, IsUserDefined: False) (MethodSymbol: null)
Operand:
ILiteralOperation (OperationKind.Literal, Type: System.Int32, Constant: 1) (Syntax: '1')
Builder method:
// MyCollection<object> x = [1];
// [CollectionBuilder(typeof(MyCollectionBuilder), "Create")]
// struct MyCollection<T> : IEnumerable<T> { ... }
// class MyCollectionBuilder
// {
// public static MyCollection<T> Create<T>(ReadOnlySpan<T> items) { ... }
// }
ICollectionExpressionOperation (1 elements, ConstructMethod: MyCollection<System.Object> MyCollectionBuilder.Create<System.Object>(System.ReadOnlySpan<System.Object> items)) (OperationKind.CollectionExpression, Type: MyCollection<System.Object>) (Syntax: '[1]')
Elements(1):
IConversionOperation (TryCast: False, Unchecked) (OperationKind.Conversion, Type: System.Object, IsImplicit) (Syntax: '1')
Conversion: CommonConversion (Exists: True, IsIdentity: False, IsNumeric: False, IsReference: False, IsUserDefined: False) (MethodSymbol: null)
Operand:
ILiteralOperation (OperationKind.Literal, Type: System.Int32, Constant: 1) (Syntax: '1')
Spread:
// int[] x = ...;
// object[] y = [..x];
ICollectionExpressionOperation (1 elements, ConstructMethod: null) (OperationKind.CollectionExpression, Type: System.Object[]) (Syntax: '[..x]')
Elements(1):
ISpreadOperation (ItemType: System.Int32) (OperationKind.Spread, Type: null, IsImplicit) (Syntax: '..x')
Operand:
ILocalReferenceOperation: x (OperationKind.LocalReference, Type: System.Int32[]) (Syntax: 'x')
ItemConversion: CommonConversion (Exists: True, IsIdentity: False, IsNumeric: False, IsReference: False, IsUserDefined: False) (MethodSymbol: null)
(Boxing)
Alternative Designs
Risks
Relates to test plan: #66418