private static bool IsImplicitStylePreferred(
UseVarPreference stylePreferences, bool isBuiltInTypeContext, bool isTypeApparentContext)
{
return(isBuiltInTypeContext
? stylePreferences.HasFlag(UseVarPreference.ForBuiltInTypes)
: isTypeApparentContext
? stylePreferences.HasFlag(UseVarPreference.WhenTypeIsApparent)
: stylePreferences.HasFlag(UseVarPreference.Elsewhere));
}
/// <summary>
/// Analyzes if type information is obvious to the reader by simply looking at the assignment expression.
/// </summary>
/// <remarks>
/// <paramref name="typeInDeclaration"/> accepts null, to be able to cater to codegen features
/// that are about to generate a local declaration and do not have this information to pass in.
/// Things (like analyzers) that do have a local declaration already, should pass this in.
/// </remarks>
public static bool IsTypeApparentInAssignmentExpression(
UseVarPreference stylePreferences,
ExpressionSyntax initializerExpression,
SemanticModel semanticModel,
ITypeSymbol typeInDeclaration,
CancellationToken cancellationToken)
{
// tuple literals
if (initializerExpression.IsKind(SyntaxKind.TupleExpression, out TupleExpressionSyntax tuple))
{
if (typeInDeclaration == null || !typeInDeclaration.IsTupleType)
{
return(false);
}
var tupleType = (INamedTypeSymbol)typeInDeclaration;
if (tupleType.TupleElements.Length != tuple.Arguments.Count)
{
return(false);
}
for (int i = 0, n = tuple.Arguments.Count; i < n; i++)
{
var argument = tuple.Arguments[i];
var tupleElementType = tupleType.TupleElements[i].Type;
if (!IsTypeApparentInAssignmentExpression(
stylePreferences, argument.Expression, semanticModel, tupleElementType, cancellationToken))
{
return(false);
}
}
return(true);
}
// default(type)
if (initializerExpression.IsKind(SyntaxKind.DefaultExpression))
{
return(true);
}
// literals, use var if options allow usage here.
if (initializerExpression.IsAnyLiteralExpression())
{
return(stylePreferences.HasFlag(UseVarPreference.ForBuiltInTypes));
}
// constructor invocations cases:
// = new type();
if (initializerExpression.IsKind(SyntaxKind.ObjectCreationExpression, SyntaxKind.ArrayCreationExpression) &&
!initializerExpression.IsKind(SyntaxKind.AnonymousObjectCreationExpression))
{
return(true);
}
// explicit conversion cases:
// (type)expr, expr is type, expr as type
if (initializerExpression.IsKind(SyntaxKind.CastExpression) ||
initializerExpression.IsKind(SyntaxKind.IsExpression) ||
initializerExpression.IsKind(SyntaxKind.AsExpression))
{
return(true);
}
// other Conversion cases:
// a. conversion with helpers like: int.Parse methods
// b. types that implement IConvertible and then invoking .ToType()
// c. System.Convert.ToType()
var memberName = GetRightmostInvocationExpression(initializerExpression).GetRightmostName();
if (memberName == null)
{
return(false);
}
if (!(semanticModel.GetSymbolInfo(memberName, cancellationToken).Symbol is IMethodSymbol methodSymbol))
{
return(false);
}
if (memberName.IsRightSideOfDot())
{
var containingTypeName = memberName.GetLeftSideOfDot();
return(IsPossibleCreationOrConversionMethod(methodSymbol, typeInDeclaration, semanticModel, containingTypeName, cancellationToken));
}
return(false);
}
