/// <inheritdoc/>
internal override bool IsAssignableFrom(TypeData sourceType, IsAssignableFromContext context)
{
if (base.IsAssignableFrom(sourceType, context))
{
return(true);
}
if (context.OnlyReferenceAndIdentityConversions == false)
{
// See if there are any user-defined implicit conversions from the source type to the target type defined in new types:
// (we want to check in new types because a breaking change in a new version due to a type change can be mitigated by
// defining an implicit conversion in one of the types in the new version).
if (DoesSourceTypeHaveImplicitOperatorOverloadToTarget(sourceType, context))
{
return(true);
}
if (DoesTargetTypeHaveImplicitOperatorOverloadFromSource(sourceType, context))
{
return(true);
}
}
return(false);
}
/// <summary>
/// Gets the value indicating whether a variable of the current type is assignable from the specified source type.
/// </summary>
/// <param name="sourceType">The source type from which to test assignability to this type.</param>
/// <param name="context">Information about the context of the IsAssignableFrom invocation.</param>
/// <returns>True if a value of the source type is assignable to a variable of the current type.</returns>
#endif
internal override bool IsAssignableFrom(TypeData sourceType, IsAssignableFromContext context)
{
if (base.IsAssignableFrom(sourceType, context))
{
return(true);
}
// From C# specification: (The implicit reference conversions are)
// - From an array-type S with an element type Se to an array-type T with an element type Te, provided all of the following are true:
// - S and T differ only in element type. In other words, S and T have the same number of dimensions.
// - Both Se and Te are reference-types.
// - An implicit reference conversion exists from Se to Te.
if (this.ElementType.IsValueType == false)
{
int sourceRank;
TypeData sourceElementType;
if (sourceType.IsArray(out sourceRank, out sourceElementType) &&
sourceElementType.IsValueType == false &&
this.ArrayRank == sourceRank)
{
return(this.ElementType.IsAssignableFrom(sourceElementType, new IsAssignableFromContext(context.NewAssemblyFamily, context.IsSourceTypeOld, onlyReferenceAndIdentityConversions: true)));
}
}
return(false);
}
/// <summary>
/// Indicates whether a variable of the current type is assignable from the specified source type.
/// </summary>
/// <param name="sourceType">The source type from which to test assignability to this type.</param>
/// <param name="context">Information about the context of the IsAssignableFrom invocation.</param>
/// <returns>True if a value of the source type is assignable to a variable of the current type.</returns>
#endif
internal virtual bool IsAssignableFrom(TypeData sourceType, IsAssignableFromContext context)
{
if (this.IsEquivalentTo(sourceType, context.NewAssemblyFamily, context.IsSourceTypeOld))
{
return(true);
}
foreach (var implicitConversionType in sourceType.GetDirectImplicitConversions(context.OnlyReferenceAndIdentityConversions))
{
if (this.IsAssignableFrom(implicitConversionType, context))
{
return(true);
}
}
return(false);
}
/// <summary>
/// Gets the value indicating whether a variable of the current type is assignable from the specified source type.
/// </summary>
/// <param name="sourceType">The source type from which to test assignability to this type.</param>
/// <param name="context">Information about the context of the IsAssignableFrom invocation.</param>
/// <returns>True if a value of the source type is assignable to a variable of the current type.</returns>
#endif
internal override bool IsAssignableFrom(TypeData sourceType, IsAssignableFromContext context)
{
if (base.IsAssignableFrom(sourceType, context))
{
return(true);
}
// Test for covariance and contravariance
if (this.SupportsVariantTypeParameters && sourceType.IsVarianceConvertibleTo(this, context))
{
return(true);
}
// From C# specification: (The implicit reference conversions are)
// - From a single-dimensional array type S[] to System.Collections.Generic.IList<T> and its base interfaces, provided that there is an implicit identity
// or reference conversion from S to T.
TypeData iListElementType;
int arrayRank;
TypeData arrayElementType;
if (this.IsIListGenericType(out iListElementType) &&
sourceType.IsArray(out arrayRank, out arrayElementType) &&
arrayRank == 1)
{
return(iListElementType.IsAssignableFrom(arrayElementType, new IsAssignableFromContext(context.NewAssemblyFamily, context.IsSourceTypeOld, onlyReferenceAndIdentityConversions: true)));
}
if (context.OnlyReferenceAndIdentityConversions == false)
{
TypeData targetUnderlyingType;
if (this.IsNullable(out targetUnderlyingType))
{
// An implicit conversion from S? to T?
TypeData sourceUnderlyingType;
if (sourceType.IsNullable(out sourceUnderlyingType))
{
return(targetUnderlyingType.IsAssignableFrom(sourceUnderlyingType, context));
}
// An implicit conversion from S to T?
return(targetUnderlyingType.IsAssignableFrom(sourceType, context));
}
}
return(false);
}
/// <inheritdoc/>
internal override bool IsAssignableFrom(TypeData sourceType, IsAssignableFromContext context)
{
if (base.IsAssignableFrom(sourceType, context))
{
return(true);
}
// Test for covariance and contravariance
if (SupportsVariantTypeParameters && sourceType.IsVarianceConvertibleTo(this, context))
{
return(true);
}
if (IsIListGenericType(out TypeData iListElementType) &&
sourceType.IsArray(out int arrayRank, out TypeData arrayElementType) &&
arrayRank == 1)
{
return(iListElementType.IsAssignableFrom(arrayElementType, new IsAssignableFromContext(context.NewAssemblyFamily, context.IsSourceTypeOld, onlyReferenceAndIdentityConversions: true)));
}
if (context.OnlyReferenceAndIdentityConversions == false)
{
if (IsNullable(out TypeData targetUnderlyingType))
{
// An implicit conversion from S? to T?
if (sourceType.IsNullable(out TypeData sourceUnderlyingType))
{
return(targetUnderlyingType.IsAssignableFrom(sourceUnderlyingType, context));
}
// An implicit conversion from S to T?
return(targetUnderlyingType.IsAssignableFrom(sourceType, context));
}
}
return(false);
}
/// <inheritdoc/>
internal override bool IsVarianceConvertibleTo(ConstructedGenericTypeData target, IsAssignableFromContext context)
{
if (target.TypeKind == TypeKind &&
target.GenericTypeDefinition == GenericTypeDefinition &&
target.GenericArguments.Count == GenericArguments.Count)
{
Debug.Assert(
target.GenericArguments.Count == GenericArguments.Count,
"Two constructed generic types from the same generic type definition should have the same number of generic arguments.");
var genericParameters = target.GenericTypeDefinition.GenericParameters;
for (int i = 0, count = genericParameters.Count; i < count; i++)
{
if (genericParameters[i].IsGenericTypeArgumentVariant(target.GenericArguments[i], GenericArguments[i], context) == false)
{
return(false);
}
}
return(true);
}
return(false);
}
private bool DoesTargetTypeHaveImplicitOperatorOverloadFromSource(TypeData sourceType, IsAssignableFromContext context)
{
var newTargetType = context.IsTargetTypeOld
? GetEquivalentNewType(context.NewAssemblyFamily) as DeclaringTypeData
: this;
if (newTargetType == null)
{
return(false);
}
var implicitOperators = newTargetType.GetMembers(OperatorData.ImplicitCastOperatorName)
.OfType <OperatorData>()
.Where(o => o.Type == newTargetType);
foreach (var op in implicitOperators)
{
if (context.IsSourceTypeOld)
{
if (op.Parameters[0].Type.IsEquivalentToOld(sourceType, context.NewAssemblyFamily))
{
return(true);
}
}
else
{
if (op.Parameters[0].Type == sourceType)
{
return(true);
}
}
}
return(false);
}
/// <summary>
/// Determines whether the variance of the type parameter allows the source type in the parameter's position to vary to the target type when the declaring
/// generic of one construction is trying to be converted to a another construction.
/// </summary>
/// <param name="targetArgument">The type in this parameter's position in the target constructed generic type.</param>
/// <param name="sourceArgument">The type in this parameter's position in the source constructed generic type.</param>
/// <param name="context">Information about the context of the IsAssignableFrom invocation.</param>
internal bool IsGenericTypeArgumentVariant(TypeData targetArgument, TypeData sourceArgument, IsAssignableFromContext context)
{
var variance = GenericParameterAttributes & GenericParameterAttributes.VarianceMask;
switch (variance)
{
case GenericParameterAttributes.None:
return(targetArgument.IsEquivalentTo(sourceArgument, context.NewAssemblyFamily, context.IsSourceTypeOld));
case GenericParameterAttributes.Contravariant:
return(sourceArgument.IsAssignableFrom(targetArgument, new IsAssignableFromContext(context.NewAssemblyFamily, context.IsSourceTypeOld, onlyReferenceAndIdentityConversions: true)));
case GenericParameterAttributes.Covariant:
return(targetArgument.IsAssignableFrom(sourceArgument, new IsAssignableFromContext(context.NewAssemblyFamily, context.IsSourceTypeOld, onlyReferenceAndIdentityConversions: true)));
default:
Debug.Fail("Unknown variance: " + variance);
return(false);
}
}
/// <summary>
/// Indicates whether the type can convert to the specified target type using type parameter variance.
/// </summary>
/// <param name="target">The target type to which this type might convert.</param>
/// <param name="context">Information about the context of the IsAssignableFrom invocation.</param>
/// <returns>True is the type is variance convertible to the target; False otherwise.</returns>
#endif
internal virtual bool IsVarianceConvertibleTo(ConstructedGenericTypeData target, IsAssignableFromContext context)
{
return(false);
}