Given a type, a name and a signature, how can I do a member lookup of the member with name name and signature signature using the C# rules of 7.4 (the 7.4 is the chapter number from the C# Language Specification) (or at least part of them... Let's say I can live with an exact match, without conversions/casts) at runtime? I need to get a MethodInfo
/PropertyInfo
/... because then I have to use it with reflection (to be more exact I'm trying to build an Expression.ForEach
builder (a factory able to create an Expression Tree that represent a foreach
statement), and to be pixel-perfect with the C# foreach
I have to be able to do duck-typing and search for a GetEnumerator
method (in the collection), a Current
property and a MoveNext
method (in the enumerator), as written in 8.8.4)
The problem (an example of the problem)
class C1
{
public int Current { get; set; }
public object MoveNext()
{
return null;
}
}
class C2 : C1
{
public new long Current { get; set; }
public new bool MoveNext()
{
return true;
}
}
class C3 : C2
{
}
var m = typeof(C3).GetMethods(); // I get both versions of MoveNext()
var p = typeof(C3).GetProperties(); // I get both versions of Current
Clearly if I try typeof(C3).GetProperty("Current")
I get an AmbiguousMatchException
exception.
A similar but different problem is present with interfaces:
interface I0
{
int Current { get; set; }
}
interface I1 : I0
{
new long Current { get; set; }
}
interface I2 : I1, I0
{
new object Current { get; set; }
}
interface I3 : I2
{
}
Here if I try to do a typeof(I3).GetProperties()
I don't get the Current
property (and this is something known, see for example GetProperties() to return all properties for an interface inheritance hierarchy), but I can't simply flatten the interfaces, because then I wouldn't know who is hiding who.
I know that probably this problem is solved somewhere in the Microsoft.CSharp.RuntimeBinder
namespace (declared in the Microsoft.CSharp
assembly). This because I'm trying to use C# rules and member lookup is necessary when you have dynamic method invocation, but I haven't been able to find anything (and then what I would get would be an Expression
or perhaps a direct invocation).
After some thought it's clear that there is something similar in the Microsoft.VisualBasic
assembly. VB.NET supports late binding. It's in Microsoft.VisualBasic.CompilerServices.NewLateBinding
, but it doesn't expose the late bounded methods.
(note: shadowing = hiding = new in method/property/event definition in C#)
No one responded, so I'll post the code I cooked in the meantime. I hate to post 400 lines of code, but I wanted to be complete. There are two main methods: GetVisibleMethods
and GetVisibleProperties
. They are extension methods of the Type
class. They will return the public visible (non-shadowed/non-overridden) methods/properties of a type. They should even handle VB.NET assemblies (VB.NET normally uses hide-by-name
shadowing instead of hidebysig
as done by C#). They cache their result in two static collections (Methods
and Properties
). The code is for C# 4.0, so I'm using ConcurrentDictionary<T, U>
. If you are using C# 3.5 you can replace it with a Dictionary<T, U>
but you have to protect it with a lock
() { } when you read from it and when you write to it.
How does it works? It works by recursion (I know that recursion is normally bad, but I hope no one will create a 1.000 level inheritance chain).
For "real" types (non-interfaces) it walks upward one level (using recursion, so this one level up could go one level up and so on) and, from the returned list of methods/properties, it removes the methods/properties it's overloading/hiding.
For interfaces it's a little more complex. Type.GetInterfaces()
returns all the interfaces that are inherited, ignoring if they are directly inherited or indirectly inherited. For each of those interfaces a list of declared methods/properties is calculated (through recursion). This list is paired with a list of methods/properties that are hidden by the interface (the HashSet<MethodInfo>
/HashSet<PropertyInfo>
). These methods/properties hidden by one interface or another are removed from all the other methods/properties returned from interfaces (so that if you have I1
with Method1(int)
, I2
inheriting from I1
that redeclares Method1(int)
and in doing so hides I1.Method1
and I3
inheriting from I1
and I2
, the fact that I2
hides I1.Method1
will be applied to the methods returned from exploring I1
, so removing I1.Method1(int)
(this happens because I don't generate an inheritance map for interfaces, I simply look at what hides what)).
From the returned collections of methods/properties one can use Linq to find the looked for method/property. Note that with interfaces you could find more than one method/property with a given signature. An example:
interface I1
{
void Method1();
}
interface I2
{
void Method1();
}
interface I3 : I1, I2
{
}
I3
will return two Method1()
.
The code:
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
public static class TypeEx
{
/// <summary>
/// Type, Tuple<Methods of type, (for interfaces)methods of base interfaces shadowed>
/// </summary>
public static readonly ConcurrentDictionary<Type, Tuple<MethodInfo[], HashSet<MethodInfo>>> Methods = new ConcurrentDictionary<Type, Tuple<MethodInfo[], HashSet<MethodInfo>>>();
/// <summary>
/// Type, Tuple<Properties of type, (for interfaces)properties of base interfaces shadowed>
/// </summary>
public static readonly ConcurrentDictionary<Type, Tuple<PropertyInfo[], HashSet<PropertyInfo>>> Properties = new ConcurrentDictionary<Type, Tuple<PropertyInfo[], HashSet<PropertyInfo>>>();
public static MethodInfo[] GetVisibleMethods(this Type type)
{
if (type.IsInterface)
{
return (MethodInfo[])type.GetVisibleMethodsInterfaceImpl().Item1.Clone();
}
return (MethodInfo[])type.GetVisibleMethodsImpl().Clone();
}
public static PropertyInfo[] GetVisibleProperties(this Type type)
{
if (type.IsInterface)
{
return (PropertyInfo[])type.GetVisiblePropertiesInterfaceImpl().Item1.Clone();
}
return (PropertyInfo[])type.GetVisiblePropertiesImpl().Clone();
}
private static MethodInfo[] GetVisibleMethodsImpl(this Type type)
{
Tuple<MethodInfo[], HashSet<MethodInfo>> tuple;
if (Methods.TryGetValue(type, out tuple))
{
return tuple.Item1;
}
var methods = type.GetMethods(BindingFlags.DeclaredOnly | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public);
if (type.BaseType == null)
{
Methods.TryAdd(type, Tuple.Create(methods, (HashSet<MethodInfo>)null));
return methods;
}
var baseMethods = type.BaseType.GetVisibleMethodsImpl().ToList();
foreach (var method in methods)
{
if (method.IsHideByName())
{
baseMethods.RemoveAll(p => p.Name == method.Name);
}
else
{
int numGenericArguments = method.GetGenericArguments().Length;
var parameters = method.GetParameters();
baseMethods.RemoveAll(p =>
{
if (!method.EqualSignature(numGenericArguments, parameters, p))
{
return false;
}
return true;
});
}
}
if (baseMethods.Count == 0)
{
Methods.TryAdd(type, Tuple.Create(methods, (HashSet<MethodInfo>)null));
return methods;
}
var methods3 = new MethodInfo[methods.Length + baseMethods.Count];
Array.Copy(methods, 0, methods3, 0, methods.Length);
baseMethods.CopyTo(methods3, methods.Length);
Methods.TryAdd(type, Tuple.Create(methods3, (HashSet<MethodInfo>)null));
return methods3;
}
private static Tuple<MethodInfo[], HashSet<MethodInfo>> GetVisibleMethodsInterfaceImpl(this Type type)
{
Tuple<MethodInfo[], HashSet<MethodInfo>> tuple;
if (Methods.TryGetValue(type, out tuple))
{
return tuple;
}
var methods = type.GetMethods(BindingFlags.DeclaredOnly | BindingFlags.Instance | BindingFlags.Public);
var baseInterfaces = type.GetInterfaces();
if (baseInterfaces.Length == 0)
{
tuple = Tuple.Create(methods, new HashSet<MethodInfo>());
Methods.TryAdd(type, tuple);
return tuple;
}
var baseMethods = new List<MethodInfo>();
var baseMethodsTemp = new MethodInfo[baseInterfaces.Length][];
var shadowedMethods = new HashSet<MethodInfo>();
for (int i = 0; i < baseInterfaces.Length; i++)
{
var tuple2 = baseInterfaces[i].GetVisibleMethodsInterfaceImpl();
baseMethodsTemp[i] = tuple2.Item1;
shadowedMethods.UnionWith(tuple2.Item2);
}
for (int i = 0; i < baseInterfaces.Length; i++)
{
baseMethods.AddRange(baseMethodsTemp[i].Where(p => !shadowedMethods.Contains(p)));
}
foreach (var method in methods)
{
if (method.IsHideByName())
{
baseMethods.RemoveAll(p =>
{
if (p.Name == method.Name)
{
shadowedMethods.Add(p);
return true;
}
return false;
});
}
else
{
int numGenericArguments = method.GetGenericArguments().Length;
var parameters = method.GetParameters();
baseMethods.RemoveAll(p =>
{
if (!method.EqualSignature(numGenericArguments, parameters, p))
{
return false;
}
shadowedMethods.Add(p);
return true;
});
}
}
if (baseMethods.Count == 0)
{
tuple = Tuple.Create(methods, shadowedMethods);
Methods.TryAdd(type, tuple);
return tuple;
}
var methods3 = new MethodInfo[methods.Length + baseMethods.Count];
Array.Copy(methods, 0, methods3, 0, methods.Length);
baseMethods.CopyTo(methods3, methods.Length);
tuple = Tuple.Create(methods3, shadowedMethods);
Methods.TryAdd(type, tuple);
return tuple;
}
private static PropertyInfo[] GetVisiblePropertiesImpl(this Type type)
{
Tuple<PropertyInfo[], HashSet<PropertyInfo>> tuple;
if (Properties.TryGetValue(type, out tuple))
{
return tuple.Item1;
}
var properties = type.GetProperties(BindingFlags.DeclaredOnly | BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public);
if (type.BaseType == null)
{
Properties.TryAdd(type, Tuple.Create(properties, (HashSet<PropertyInfo>)null));
return properties;
}
var baseProperties = type.BaseType.GetVisiblePropertiesImpl().ToList();
foreach (var property in properties)
{
if (property.IsHideByName())
{
baseProperties.RemoveAll(p => p.Name == property.Name);
}
else
{
var indexers = property.GetIndexParameters();
baseProperties.RemoveAll(p =>
{
if (!property.EqualSignature(indexers, p))
{
return false;
}
return true;
});
}
}
if (baseProperties.Count == 0)
{
Properties.TryAdd(type, Tuple.Create(properties, (HashSet<PropertyInfo>)null));
return properties;
}
var properties3 = new PropertyInfo[properties.Length + baseProperties.Count];
Array.Copy(properties, 0, properties3, 0, properties.Length);
baseProperties.CopyTo(properties3, properties.Length);
Properties.TryAdd(type, Tuple.Create(properties3, (HashSet<PropertyInfo>)null));
return properties3;
}
private static Tuple<PropertyInfo[], HashSet<PropertyInfo>> GetVisiblePropertiesInterfaceImpl(this Type type)
{
Tuple<PropertyInfo[], HashSet<PropertyInfo>> tuple;
if (Properties.TryGetValue(type, out tuple))
{
return tuple;
}
var properties = type.GetProperties(BindingFlags.DeclaredOnly | BindingFlags.Instance | BindingFlags.Public);
var baseInterfaces = type.GetInterfaces();
if (baseInterfaces.Length == 0)
{
tuple = Tuple.Create(properties, new HashSet<PropertyInfo>());
Properties.TryAdd(type, tuple);
return tuple;
}
var baseProperties = new List<PropertyInfo>();
var basePropertiesTemp = new PropertyInfo[baseInterfaces.Length][];
var shadowedProperties = new HashSet<PropertyInfo>();
for (int i = 0; i < baseInterfaces.Length; i++)
{
var tuple2 = baseInterfaces[i].GetVisiblePropertiesInterfaceImpl();
basePropertiesTemp[i] = tuple2.Item1;
shadowedProperties.UnionWith(tuple2.Item2);
}
for (int i = 0; i < baseInterfaces.Length; i++)
{
baseProperties.AddRange(basePropertiesTemp[i].Where(p => !shadowedProperties.Contains(p)));
}
foreach (var property in properties)
{
if (property.IsHideByName())
{
baseProperties.RemoveAll(p =>
{
if (p.Name == property.Name)
{
shadowedProperties.Add(p);
return true;
}
return false;
});
}
else
{
var indexers = property.GetIndexParameters();
baseProperties.RemoveAll(p =>
{
if (!property.EqualSignature(indexers, p))
{
return false;
}
shadowedProperties.Add(p);
return true;
});
}
}
if (baseProperties.Count == 0)
{
tuple = Tuple.Create(properties, shadowedProperties);
Properties.TryAdd(type, tuple);
return tuple;
}
var properties3 = new PropertyInfo[properties.Length + baseProperties.Count];
Array.Copy(properties, 0, properties3, 0, properties.Length);
baseProperties.CopyTo(properties3, properties.Length);
tuple = Tuple.Create(properties3, shadowedProperties);
Properties.TryAdd(type, tuple);
return tuple;
}
private static bool EqualSignature(this MethodInfo method1, int numGenericArguments1, ParameterInfo[] parameters1, MethodInfo method2)
{
// To shadow by signature a method must have same name, same number of
// generic arguments, same number of parameters and same parameters' type
if (method1.Name != method2.Name)
{
return false;
}
if (numGenericArguments1 != method2.GetGenericArguments().Length)
{
return false;
}
var parameters2 = method2.GetParameters();
if (!parameters1.EqualParameterTypes(parameters2))
{
return false;
}
return true;
}
private static bool EqualSignature(this PropertyInfo property1, ParameterInfo[] indexers1, PropertyInfo property2)
{
// To shadow by signature a property must have same name,
// same number of indexers and same indexers' type
if (property1.Name != property2.Name)
{
return false;
}
var parameters2 = property1.GetIndexParameters();
if (!indexers1.EqualParameterTypes(parameters2))
{
return false;
}
return true;
}
private static bool EqualParameterTypes(this ParameterInfo[] parameters1, ParameterInfo[] parameters2)
{
if (parameters1.Length != parameters2.Length)
{
return false;
}
for (int i = 0; i < parameters1.Length; i++)
{
if (parameters1[i].IsOut != parameters2[i].IsOut)
{
return false;
}
if (parameters1[i].ParameterType.IsGenericParameter)
{
if (!parameters2[i].ParameterType.IsGenericParameter)
{
return false;
}
if (parameters1[i].ParameterType.GenericParameterPosition != parameters2[i].ParameterType.GenericParameterPosition)
{
return false;
}
}
else if (parameters1[i].ParameterType != parameters2[i].ParameterType)
{
return false;
}
}
return true;
}
private static bool IsHideByName(this MethodInfo method)
{
if (!method.Attributes.HasFlag(MethodAttributes.HideBySig) && (!method.Attributes.HasFlag(MethodAttributes.Virtual) || method.Attributes.HasFlag(MethodAttributes.NewSlot)))
{
return true;
}
return false;
}
private static bool IsHideByName(this PropertyInfo property)
{
var get = property.GetGetMethod();
if (get != null && get.IsHideByName())
{
return true;
}
var set = property.GetSetMethod();
if (set != null && set.IsHideByName())
{
return true;
}
return false;
}
}
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