NetFabric.CodeAnalysis 4.2.2

NetFabric.CodeAnalysis

This package extends the API provided by Roslyn. It can be used in the development of Roslyn Analyzers and Source Generators.

Enumerable type checking

To find if a type is enumerable, it's not enough to check if it implements IEnumerable, IEnumerable<> or IAsyncEnumerable<>. The foreach and await foreach statements support several other cases.

NOTE: Check the article "Efficient Data Processing: Leveraging C#'s foreach Loop" to understand all the possible cases supported by the foreach statement.

This package provides extension methods for the interface ITypeSymbol that can correctly validate if the type it represents can be used as the source in foreach or await foreach statements.

IsEnumerable and IsEnumerator

public static bool IsEnumerable(this ITypeSymbol typeSymbol,
    Compilation compilation,
    [NotNullWhen(true)] out EnumerableSymbols? enumerableSymbols,
    out Errors errors);

public static bool IsEnumerator(this ITypeSymbol typeSymbol,
    Compilation compilation,
    out Errors errors);

The methods return true if the type represented by ITypeSymbol can be used in a foreach statement; otherwise false. It supports all the cases including when GetEnumerator() is defined as an extension method.

IsEnumerable() calls IsEnumerator() internally to validate the type returned by GetEnumerator(). The method IsEnumerable() only returns true if both the enumerable and the enumerator are valid.

If the method IsEnumerable() returns true, the enumerableSymbols output parameter contains all the IMethodInfo and IPropertySymbol for the methods and properties that are going to be actually used by the foreach statement. The GetEnumerator() of the enumerable, the property Current and the method MoveNext() of the enumerator. It may also contain info for methods Reset() and Dispose() of the enumerator, if defined.

Is the methods return false, the errors output parameter indicates why the type is not considered an enumerable. It can be a combination of Error.MissingGetEnumerator, Error.MissingCurrent and Error.MissingMoveNext.

The output parameter also includes a ForEachUsesIndexer boolean property that indicates that, although the collection provides an enumerator, foreach will use the indexer instead. That's the case for arrays and spans.

You can use these info values to further validate the enumerable and its respective enumerator. For example, use the following to find if the Current property of the enumerator returns by reference:

enumerableSymbols.EnumeratorSymbols.Current.ReturnsByRef;

IsAsyncEnumerable and IsAsyncEnumerator

public static bool IsAsyncEnumerable(this ITypeSymbol typeSymbol,
    Compilation compilation,
    [NotNullWhen(true)] out AsyncEnumerableSymbols? enumerableSymbols,
    out Errors errors);

public static bool IsAsyncEnumerator(this ITypeSymbol typeSymbol,
    Compilation compilation,
    out Errors errors);

The methods return true if the type represented by ITypeSymbol can be used in an await foreach statement; otherwise false. It supports all the cases including when GetAsyncEnumerator() is defined as an extension method.

IsAsyncEnumerable() calls IsAsyncEnumerator() internally to validate the type returned by GetAsyncEnumerator(). The method IsAsyncEnumerable() only returns true if both the enumerable and the enumerator are valid.

If the method IsAsyncEnumerable() returns true, the enumerableSymbols output parameter contains all the IMethodInfo and IPropertySymbol for the methods and properties that are going to be actually used by the await foreach statement. The GetAsyncEnumerator() of the enumerable, the property Current and the method MoveNextAsync() of the enumerator. It may also contain info for method DisposeAsync() of the enumerator, if defined.

Is the methods return false, the errors output parameter indicates why the type is not considered an enumerable. It can be a combination of Error.MissingGetEnumerator, Error.MissingCurrent and Error.MissingMoveNext.

You can use these info values to further validate the async enumerable or its respective enumerator.