How can I determine if an implicit cast exists in C#?

Question

I have two types, T and U, and I want to know whether an implicit cast operator is defined from T to U.

I\'m aware of the existence of IsAssignableFrom, and this is not

Answer 1

Here's a solution I found. The major code shown as bellow (after some simple translation):

public static bool IsImplicitFrom(this Type type, Type fromType) {
    if (type == null || fromType == null) {
        return false;
    }

    // support for reference type
    if (type.IsByRef) { type = type.GetElementType(); }
    if (fromType.IsByRef) { fromType = type.GetElementType(); }

    // could always be convert to object
    if (type.Equals(typeof(object))) {
        return true;
    }

    // check if it could be convert using standard implicit cast
    if (IsStandardImplicitFrom(type, fromType)) {
        return true;
    }

    // determine implicit convert operator
    Type nonNullalbeType, nonNullableFromType;
    if (IsNullableType(type, out nonNullalbeType) && 
        IsNullableType(fromType, out nonNullableFromType)) {
        type = nonNullalbeType;
        fromType = nonNullableFromType;
    }

    return ConversionCache.GetImplicitConversion(fromType, type) != null;
}

internal static bool IsStandardImplicitFrom(this Type type, Type fromType) {
    // support for Nullable
    if (!type.IsValueType || IsNullableType(ref type)) {
        fromType = GetNonNullableType(fromType);
    }

    // determine implicit value type convert
    HashSet typeSet;
    if (!type.IsEnum && 
        ImplicitNumericConversions.TryGetValue(Type.GetTypeCode(type), out typeSet)) {
        if (!fromType.IsEnum && typeSet.Contains(Type.GetTypeCode(fromType))) {
            return true;
        }
    }

    // determine implicit reference type convert and boxing convert
    return type.IsAssignableFrom(fromType);
}

Update: Here's the whole file.