switch.cs

    [Pure, ContractAnnotation("null => null")]
    public static ICSharpTreeNode GetCodeBody([CanBeNull] this ICSharpDeclaration declaration)
    {
      if (declaration == null) return null;

      var functionDeclaration = declaration as ICSharpFunctionDeclaration;
      if (functionDeclaration != null && functionDeclaration.Body != null)
      {
        return functionDeclaration.Body;
      }

      var localFunctionDeclaration = declaration as ILocalFunctionDeclaration;
      if (localFunctionDeclaration != null)
      {
        var body = localFunctionDeclaration.Body;
        if (body != null) return body;
      }

      var expressionBodyOwner = declaration as IExpressionBodyOwnerDeclaration;
      if (expressionBodyOwner != null)
      {
        var clause = expressionBodyOwner.ArrowExpression;
        if (clause != null) return clause.Expression;
      }

      var lambdaExpression = declaration as ILambdaExpression;
      if (lambdaExpression != null)
      {
        return lambdaExpression.BodyExpression
            ?? lambdaExpression.BodyBlock as ICSharpTreeNode;
      }

      var anonymousMethodExpression = declaration as IAnonymousMethodExpression;
      if (anonymousMethodExpression != null)
      {
        return anonymousMethodExpression.Body;
      }

      return null;
    }

switch2.cs

    [Pure, ContractAnnotation("null => null")]
    public static ICSharpTreeNode GetCodeBody([CanBeNull] this ICSharpDeclaration declaration)
    {
      switch (declaration)
      {
        case ICSharpFunctionDeclaration functionDeclaration when functionDeclaration.Body != null:
          return functionDeclaration.Body;
          
        case ILocalFunctionDeclaration localFunctionDeclaration when localFunctionDeclaration.Body != null:
          return localFunctionDeclaration.Body;
          
        case IExpressionBodyOwnerDeclaration expressionBodyOwner when expressionBodyOwner.ArrowExpression != null:
          return localFunctionDeclaration.ArrowExpression.Expression;
        
        case ILambdaExpression lambdaExpression:
          return lambdaExpression.BodyExpression ?? lambdaExpression.BodyBlock as ICSharpTreeNode;
          
        case IAnonymousMethodExpression anonymousMethodExpression:
          return anonymousMethodExpression.Body;
          
        default:
          return null;
      }
    }

switch3.cs

    [Pure, ContractAnnotation("null => null")]
    public static ICSharpTreeNode GetCodeBody([CanBeNull] this ICSharpDeclaration declaration)
    {
      switch (declaration)
      {
        case ICSharpFunctionDeclaration { Body is var! bodyBlock }:
          return bodyBlock;

        case ILocalFunctionDeclaration { Body is var! bodyBlock }:
          return bodyBlock;
          
        case IExpressionBodyOwnerDeclaration { ArrowExpression is { Expression is var bodyExpression } }:
          return bodyExpression;
        
        case ILambdaExpression lambdaExpression:
          return lambdaExpression.BodyExpression ?? lambdaExpression.BodyBlock as ICSharpTreeNode;
          
        case IAnonymousMethodExpression anonymousMethodExpression:
          return anonymousMethodExpression.Body;
          
        default:
          return null;
      }
    }