private static MethodCallCSharpExpression MakeAccess(ConditionalReceiver receiver, MethodInfo method, ReadOnlyCollection <ParameterAssignment> arguments)
{
if (method.IsStatic && method.IsDefined(typeof(ExtensionAttribute)))
{
var thisPar = method.GetParametersCached()[0];
var thisArg = CSharpExpression.Bind(thisPar, receiver);
var newArgs = new ParameterAssignment[arguments.Count + 1];
newArgs[0] = thisArg;
var i = 1;
foreach (var arg in arguments)
{
newArgs[i++] = arg;
}
var newArguments = new TrueReadOnlyCollection <ParameterAssignment>(newArgs);
return(CSharpExpression.Call(null, method, newArguments)); // TODO: call ctor directly
}
else
{
return(CSharpExpression.Call(receiver, method, arguments)); // TODO: call ctor directly
}
}
protected internal override Expression VisitConditionalReceiver(ConditionalReceiver node)
{
var id = _parent.MakeInstanceId(node);
var res = new XElement(nameof(ConditionalReceiver), new XAttribute("Id", id), new XAttribute(nameof(node.Type), node.Type));
_nodes.Push(res);
return(node);
}
protected internal override Expression VisitConditionalReceiver(ConditionalReceiver node)
{
// TODO: We could check that we find the receiver exactly once.
if (node == _receiver)
{
return(_nonNull);
}
return(base.VisitConditionalReceiver(node));
}
internal static void CheckConditionalAccess(Expression receiver, ConditionalReceiver nonNullReceiver, Expression whenNotNull)
{
RequiresCanRead(receiver, nameof(receiver));
RequiresNotNull(nonNullReceiver, nameof(nonNullReceiver));
RequiresCanRead(whenNotNull, nameof(whenNotNull));
var receiverType = receiver.Type;
if (receiverType == typeof(void) || receiverType.IsByRef || (receiverType.IsValueType && !receiverType.IsNullableType()))
{
throw Error.InvalidConditionalReceiverExpressionType(receiverType);
}
var nonNullReceiverType = receiverType.GetNonNullReceiverType();
if (nonNullReceiverType != nonNullReceiver.Type)
{
throw Error.ConditionalReceiverTypeMismatch(receiverType, nonNullReceiverType);
}
}
internal override ConditionalAccessCSharpExpression <Expression> Rewrite(Expression receiver, ConditionalReceiver nonNullReceiver, Expression whenNotNull) => new ConditionalAccessCSharpExpression(receiver, nonNullReceiver, whenNotNull);
public SubstituteConditionalReceiver(ConditionalReceiver receiver, Expression nonNull)
{
_receiver = receiver;
_nonNull = nonNull;
}
internal override ConditionalAccessCSharpExpression <MemberExpression> Rewrite(Expression receiver, ConditionalReceiver nonNullReceiver, MemberExpression whenNotNull)
{
return(new ConditionalMemberCSharpExpression(receiver, nonNullReceiver, whenNotNull));
}
private ConditionalMemberCSharpExpression(Expression expression, ConditionalReceiver receiver, MemberExpression access)
: base(expression, receiver, access)
{
}
internal override ConditionalAccessCSharpExpression <IndexCSharpExpression> Rewrite(Expression receiver, ConditionalReceiver nonNullReceiver, IndexCSharpExpression whenNotNull)
{
return(new MethodBased(receiver, nonNullReceiver, whenNotNull));
}
private MethodBased(Expression @object, ConditionalReceiver receiver, IndexCSharpExpression access)
: base(@object, receiver, access)
{
}
private ConditionalArrayIndexCSharpExpression(Expression array, ConditionalReceiver receiver, IndexExpression access)
: base(array, receiver, access)
{
}
private ConditionalArrayIndexCSharpExpression(Expression array, ConditionalReceiver receiver, ReadOnlyCollection <Expression> indexes)
: this(array, receiver, MakeAccess(receiver, indexes))
{
}
private XNode Visit(ConditionalReceiver node)
{
VisitConditionalReceiver(node);
return(_nodes.Pop());
}
public ConditionalReceiverProxy(ConditionalReceiver node)
{
_node = node;
}
protected internal virtual Expression VisitConditionalReceiver(ConditionalReceiver node)
{
return(node);
}
private ConditionalMethodCallCSharpExpression(Expression expression, ConditionalReceiver receiver, MethodInfo method, ReadOnlyCollection <ParameterAssignment> arguments)
: this(expression, receiver, MakeAccess(receiver, method, arguments))
{
}
private MethodBased(Expression @object, ConditionalReceiver receiver, MethodInfo method, ReadOnlyCollection <ParameterAssignment> arguments)
: this(@object, receiver, MakeAccess(receiver, method, arguments))
{
_method = method;
}
private static IndexExpression MakeAccess(ConditionalReceiver receiver, ReadOnlyCollection <Expression> indexes)
{
return(Expression.ArrayAccess(receiver, indexes)); // TODO: call ctor directly
}
private static IndexCSharpExpression MakeAccess(ConditionalReceiver receiver, MethodInfo method, ReadOnlyCollection <ParameterAssignment> arguments)
{
return(CSharpExpression.Index(receiver, method, arguments)); // TODO: call ctor directly
}
private ConditionalInvocationCSharpExpression(Expression expression, ConditionalReceiver receiver, ReadOnlyCollection <ParameterAssignment> arguments)
: this(expression, receiver, MakeAccess(receiver, arguments))
{
}
private ConditionalMemberCSharpExpression(Expression expression, ConditionalReceiver receiver, MemberInfo member)
: this(expression, receiver, MakeAccess(receiver, member))
{
}
private ConditionalInvocationCSharpExpression(Expression expression, ConditionalReceiver receiver, InvocationCSharpExpression access)
: base(expression, receiver, access)
{
}
private static MemberExpression MakeAccess(ConditionalReceiver receiver, MemberInfo member)
{
return(Expression.MakeMemberAccess(receiver, member)); // TODO: call ctor directly
}
private static InvocationCSharpExpression MakeAccess(ConditionalReceiver receiver, ReadOnlyCollection <ParameterAssignment> arguments)
{
return(CSharpExpression.Invoke(receiver, arguments)); // TODO: call ctor directly
}
internal ConditionalAccessCSharpExpression(Expression receiver, ConditionalReceiver nonNullReceiver, Expression whenNotNull)
: base(receiver, nonNullReceiver, whenNotNull)
{
}
internal override ConditionalAccessCSharpExpression <InvocationCSharpExpression> Rewrite(Expression receiver, ConditionalReceiver nonNullReceiver, InvocationCSharpExpression whenNotNull)
{
return(new ConditionalInvocationCSharpExpression(receiver, nonNullReceiver, whenNotNull));
}
public ConditionalReceiverProxy(ConditionalReceiver node)
{
_node = node;
}
private PropertyBased(Expression @object, ConditionalReceiver receiver, PropertyInfo indexer, ReadOnlyCollection <ParameterAssignment> arguments)
: this(@object, receiver, MakeAccess(receiver, indexer, arguments))
{
}
/// <summary>
/// Creates a <see cref="ConditionalAccessCSharpExpression"/> representing a null-conditional access operation.
/// </summary>
/// <param name="receiver">The receiver to access conditionally.</param>
/// <param name="nonNullReceiver">The non-null receiver used in the <paramref name="whenNotNull"/> expression.</param>
/// <param name="whenNotNull">The operation to apply to the receiver when it's non-null.</param>
/// <returns>A <see cref="Microsoft.CSharp.Expressions.ConditionalReceiver"/> that has the <see cref="CSharpNodeType" /> property equal to <see cref="CSharpExpressionType.ConditionalReceiver" /> and the <see cref="Expression.Type" /> property equal to the specified type.</returns>
public static ConditionalAccessCSharpExpression ConditionalAccess(Expression receiver, ConditionalReceiver nonNullReceiver, Expression whenNotNull)
{
CheckConditionalAccess(receiver, nonNullReceiver, whenNotNull);
// TODO: More elaborate checking of `whenNotNull` would be possible, in particular to check the following:
//
// - only supported operations can occur in the access expression
// - the conditional receiver is used in an input position
// - the conditional receiver is used exactly once
//
// The only drawback is that those checks will involve a visit to the access expression, which doesn't have a
// constant cost. When those nodes are deeply nested, we'd be going over the same tree many times, unless we
// relax the check for the conditional receiver usage count to be at least once. This would also happen during
// a rewrite of the tree by means of a visitor, which causes factory invocations.
//
// Note that the expression compiler can still catch such violations during reduction by only reducing one
// occurrence of each conditional receiver, therefore leaving any other occurrences unbound, which on its turn
// causes a reduction error for the unbound conditional receiver (which is not a reducible node).
//
// What are the implications of not performing those checks? Nothing unsafe will happen but the node type will
// effectively capture a superset of the possibilities provided by the C# language for the construct. E.g.
// you could construct a null-conditional call where the conditional receiver is used for a parameter that's
// different from the receiving instance (or the `this` parameter for an extension method):
//
// ConditionalAccess(bar, receiver, Call(foo, qux, { receiver })) == foo.qux(bar) iff bar != null
// ^^^ ~~~~~~~~
// instance argument
//
// We could decide the cost of checking doesn't yield enough benefits given that it only applies to hand-
// crafted expressions (i.e. the compiler will never emit a non-standard form). We'd still have to support
// this behavior in future versions and consider it to have well-defined behavior, or document it as having
// undefined behavior (with little predecents) from the get-go.
//
// Finally, note that we could do away with this problem by modeling the nodes differently without relying on
// a node for the conditional receiver. To do so, we'd have to introduce expressions for argument lists that
// don't include the receiver, which duplicates a lot of existing LINQ nodes. In such a design, the receiver
// would be implicit and always correspond to the "left-most source" in the access expression. It comes at
// the cost of not being able to reuse existing LINQ nodes which always have a bound receiver, but we could
// piggyback on the work to introduce C#-specific nodes for e.g. ParameterAssignment to create nodes for e.g.
// argument lists. Old LINQ nodes could be considered applications of more primitive partial nodes:
//
// Call(o, m, args) == Access(o, Call(m, args)) == o.m(args)
// Member(o, p) == Access(o, Member(p)) == o.p
// Index(o, i, args) == Access(o, Index(i, args)) == o.i[args]
// Invoke(f, args) == Access(f, Invoke(args)) == o(args)
//
// In this setting, we could still allow further composition of the access expressions by passing a list of
// access operations in lieu of the second operand to `Access`, e.g.
//
// Access(o, { Member(p), Call(m, args2) }) == o.p.m(args2)
//
// Substituting `Access` for `ConditionalAccess` would mean the following:
//
// ConditionalAccess(o, { Member(p), Call(m, args2) }) == o?.p.m(args2)
//
// Note that it makes for a much stranger tree representation (though arguably the current form is weird too)
// with new partially applied `Member`, `Call`, `Index`, and `Invoke` constructs. Instead, we could nest them
// as well, by only having one (inner-most, left-most) access-unbound node in the access expression:
//
// ConditionalAccess(o, Call(Member( p), m, args2))
// ^^
// hole
//
// With this form, the check is still expensive, because we need to check for exactly one unbound form in the
// source chain of the access expression.
// DESIGN: We could make instances of type ConditionalAccessCSharpExpression<TExpression> and/or specialized subtypes
// if we decide to keep those. However, it may look strange if `whenNotNull` is not just a single access but
// consists of a 'chain' of operations. Right now, the idea is to have the specialized subtypes merely as a
// convenience when using factories by hand, but we could scrap it all and just stick with the primitive node.
return(new ConditionalAccessCSharpExpression(receiver, nonNullReceiver, whenNotNull));
}
internal ConditionalIndexCSharpExpression(Expression expression, ConditionalReceiver receiver, IndexCSharpExpression access)
: base(expression, receiver, access)
{
}
protected internal virtual Expression VisitConditionalReceiver(ConditionalReceiver node)
{
return node;
}
internal override ConditionalAccessCSharpExpression <IndexCSharpExpression> Rewrite(Expression receiver, ConditionalReceiver nonNullReceiver, IndexCSharpExpression whenNotNull) => new PropertyBased(receiver, nonNullReceiver, whenNotNull);
