I've implemented IDynamicObject in C# 4, return a custom MetaObject subclass that does simple property getter/setter dispatch to a Dictionary. Not rocket science.
If I do this:
dynamic foo = new DynamicFoo();
foo.Name = "Joe";
foo.Name = "Fred";
Console.WriteLine(foo.Name);
Then 'Joe' is printed to the console... the second call to the 'Name' setter is never invoked (never steps into my custom dispatcher code at all).
I know the DLR does callsite caching, but I assumed that wouldn't apply here. Anyone know what's going on?
Whatever MetaObject you're returning from (Bind)SetMember will be cached and re-used in this case. You have 2 dynamic sites doing sets. The 1st call will cache the result in an L2 cache which the 2nd site will pick up before asking you to produce a new rule.
So whatever MetaObject you're returning needs to include an expression tree that will update the value. For example it should do something like:
return new MetaObject(
Expression.AssignProperty(this.Expression, value.Expression),
Restrictions.TypeRestriction(this.Expression, this.Value.GetType());
Related
The asp-items Razor "TagHelper" will add an <option> to a <select> for each value in the SelectList. I want to modify each of those children.
Specifically I want to disable some of them (i.e. add disabled="disabled").
Even more specifically I want to dynamically disable some of them; I'm using angular so I could ng-disabled="{dynamic_boolean_which_determines_disabled}". This means the option could be disabled at first, but after user makes a change, the option could be disabled (without page reload). Angular should take care of this; I think Angular and TagHelpers should work together in theory...
I expected:
I could somehow access an IEnumerable of the children <option> tags that would be created (i.e. one for each item in the SelectList), iterate the children tags, and SetAttribute("disabled") or SetAttribute("ng-disabled")...
I tried:
Creating my own TagHelper which targets the select[asp-items], and tries to GetChildContentAsync() and/or SetContent to reach an IEnumerable <option> tags and iterate them and process each, but I think this will only let me modify the entire InnerHtml as a string; feels hacky to do a String.replace, but I could do it if that's my only option? i.e. ChildrenContent.Replace("<option", "<option disabled=\"...\"")
Creating my own TagHelper which targets the option elements that are children of the select[asp-items], so I can individually process each. This works, but not on the dynamically-added <option> created by asp-items, it only works on "literal" <option> tags that I actually put into my cshtml markup.
I think this'll work but not ideal:
As I said above, I think I can get the result of TagHelper's dynamic asp-items <option></option> <option></option>, as a string, and do a string replace, but I prefer not to work with strings directly...
I suspect (I haven't tried it) that I could just do the work of asp-items myself; i.e. custom-items. But then I'm recreating the wheel by re-doing the work which asp-items could've done for me?
So I hadn't yet read the "AutoLinkHttpTagHelper" in the example which uses string replacement (specifically RegEx replace) to replace every occurrence of a URL, with an <a> pointed at that URL. The cases are slightly different*, but...
Anyway, here's my solution once I learned to stop worrying and love the string modification:
[HtmlTargetElement("select", Attributes = "asp-items")]
public class AspItemsNgDisabledTagHelper : SelectTagHelper
{
//Need it to process *after* the SelectTagHelper
public override int Order { get; } = int.MaxValue;
//https://learn.microsoft.com/en-us/aspnet/core/mvc/views/tag-helpers/authoring#ProcessAsync
public AspItemsNgDisabledTagHelper(IHtmlGenerator gen) : base(gen) {}
public override void Process(TagHelperContext context, TagHelperOutput output)
{
//Notice I'm getting the PostContent;
//SelectTagHelper leaves its literal content (i.e. in your CSHTML, if there is any) alone ; that's Content
//it only **appends** new options specified; that's PostContent
//Makes sense, but I still wasn't expecting it
var generated_options = output.PostContent.GetContent();
//Note you do NOT need to extend SelectTagHelper as I've done here
//I only did it to take advantage of the asp-for property, to get its Name, so I could pass that to the angular function
var select_for = this.For.Name;
//The heart of the processing is a Regex.Replace, just like
//their example https://learn.microsoft.com/en-us/aspnet/core/mvc/views/tag-helpers/authoring#inspecting-and-retrieving-child-content
var ng_disabled_generated_options = Regex.Replace(
generated_options,
"<option value=\"(\\w+)\">",
$"<option value=\"$1\" ng-disabled=\"is_disabled('{select_for}', '$1')\">");
//Finally, you Set your modified Content
output.PostContent.SetHtmlContent(ng_disabled_generated_options);
}
}
Few learning opportunities:
Was thinking I'd find AspForTagHelper and AspItemsTagHelper, (angular background suggested that the corresponding attributes; asp-for and asp-items, would be separate "directives" aka TagHelper).
In fact, TagHelper "matching" focuses on the element name (unlike angular which can match element name... attribute... class... CSS selector)
Therefore I found what I was looking for in SelectTagHelper, which has For and Items as properties. Makes sense.
As I said above, I extend SelectTagHelper, but that's not necessary to answer my original question. It's only necessary if you want access to the this.For.Name as I've done, but there may even be a way around that (i.e. re-bind its own For property here?)
I got on a distraction thinking I would need to override the SelectTagHelper's behavior to achieve my goals; i.e. Object-Oriented Thinking. In fact, even if I did extend SelectTagHelper, that doesn't stop a separate instance of the base SelectTagHelper from matching and processing the element. In other words, element processing happens in a pipeline.
This explains why extending and calling base.Process(), will result in Select doing its job twice; once when your instance matches, and again when the base instance matched.
(I suppose could've prevented SelectTagHelper from matching by creating a new element name like <asp-items-select>? But, not necessary... I just avoid calling base.Process(). So unless that's a bad practice...)
*Different in this way:
They want to create a tag where none exists, whereas I want to add an attribute a tag which is already there; i.e. the <option>
Though the <option> "tag" is generated by the SelectTagHelper in its PostContent (was expecting to find it in Content), and I don't think tags-generated-in-strings-by-content-mods can be matched with their corresponding TagHelper -- so maybe we really are the same in that we're just dealing with plain old strings
Their "data" aka "model" is implied in the text itself; they find a URL and that URL string becomes a unit of meaning they use. In my case, there is an explicit class for Modeling; the SelectList (<select>) which consists of some SelectListItem (<option>) -- but that class doesn't help me either.
That class only gives me attributes like public bool Disabled (remember, this isn't sufficient for me because the value of disabled could change to true or false within browser; i.e. client-side only), and public SelectListGroup Group -- certainly nothing as nonstandard as ng-disabled, nor a "catch-all" property like Attributes which could let me put arbitrary attributes (ng-disabled or anything else) in there.
I am attempting to use the Roslyn SDK and StackExchange.Precompilation (thank you!) to implement aspect-oriented programming in C#6. My specific problem right now is, starting with an IdentifierNameSyntax instance, I want to find the "member type" (method, property, field, var, etc.) that the identifier refers to. (How) can this be done?
Background:
The first proof-of-concept I am working on is some good old design-by-contract. I have a NonNullAttribute which can be applied to parameters, properties, or method return values. Along with the attribute there is a class implementing the StackExchange.Precompilation.ICompileModule interface, which on compilation will insert null checks on the marked parameters or return values.
This is the same idea as PostSharp's NonNullAttribute, but the transformation is being done on one of Roslyn's syntax trees, not on an already compiled assembly. It is also similar to Code Contracts, but with a declarative attribute approach, and again operating on syntax trees not IL.
For example, this source code:
[return: NonNull]
public string Capitalize([NonNull] string text) {
return text.ToUpper();
}
will be transformed into this during precompilation:
[return: NonNull]
public string Capitalize([NonNull] string text) {
if (Object.Equals(text, null))
throw new ArgumentNullException(nameof(text));
var result = text.ToUpper();
if (Object.Equals(result, null))
throw new PostconditionFailedException("Result cannot be null.");
return result;
}
(PostconditionFailedException is a custom exception I made to compliment ArgumentException for return values. If there is already something like this in the framework please let me know.)
For properties with this attribute, there would be a similar transformation, but with preconditions and postconditions implemented separately in the set and get accessors, respectively.
The specific reason I need to find the "member type" of an identifier here is for an optimization on implementing postconditions. Note in the post-compilation sample above, the value that would have been returned is stored in a local variable, checked, and then the local is returned. This storage is necessary for transforming return statements that evaluate a method or complex expression, but if the returned expression is just a field or local variable reference, creating that temporary storage local is wasteful.
So, when the return statement is being scanned, I first check if the statement is of the form ReturnKeyword-IdentifierSyntaxToken-SemicolonToken. If so, I then need to check what that identifier refers to, so I avoid that local variable allocation if the referent is a field or var.
Update
For more context, check out the project this is in reference to on GitHub.
You'll need to use SemanticModel.GetSymbolInfo to determine the symbol an identifier binds to.
Use SemanticModel.GetTypeInfo.Type to obtain the TypeInfo and use it to explore the Type
when I use spring cache with redis, I use it in two app, the one read and write,the other is only read,how can I config?
I try do like this, but it does not work!
#Cacheable(value = "books", key = "#isbn", condition = "false")
Can anyone help ?
You have misunderstood the purpose of the #Cacheable annotation's "condition" attribute. Per the documentation...
If true, the method is cached - if not, it behaves as if the method is
not cached, that is executed every since time no matter what values
are in the cache or what arguments are used.
The condition attribute just determines whether the cache (e.g. Redis) is consulted first, before executing the (potentially expensive) method. If condition evaluates to false, then the method will always be executed and the result subsequently cached.
In the read-only app, I am assuming you want the cache consulted first, if the value is not in the cache, then execute the method, however, DO NOT cache the result. Is this correct?
If so, then you only need specify the unless attribute instead of the condition attribute like so...
#Cacheable(value="books", key="#isbn", unless="true")
void someBookMutatingOperation(String isbn, ...) { .. }
If, however, you want to avoid the cacheable method invocation in the read-only (version of the) app altogether and just consult the cache regardless of whether a value actually exists in the cache or not, then your problem is quite a bit more complex/difficult.
Spring's Cache Abstraction operates on the premise that if a value is not in the cache then it will return null to indicate a cache miss, which is then followed by a subsequent method invocation. Only when a cache returns a value for the specified key(s) will the method invocation be avoided.
Without a custom extension (perhaps using (additional) AOP interceptors) there is no way to avoid the OOTB behavior.
I will not elaborate on this later technique unless your use case requires it.
Hope this helps.
#John Blum
thanks! happy new year.
your answer inspired me, I have read a part of the spring cache source code. the CacheInterceptor class. the CacheAspectSupport class.
private Object execute(CacheOperationInvoker invoker, CacheOperationContexts contexts) {
// Process any early evictions
processCacheEvicts(contexts.get(CacheEvictOperation.class), true, ExpressionEvaluator.NO_RESULT);
// Check if we have a cached item matching the conditions
Cache.ValueWrapper cacheHit = findCachedItem(contexts.get(CacheableOperation.class));
// Collect puts from any #Cacheable miss, if no cached item is found
List<CachePutRequest> cachePutRequests = new LinkedList<CachePutRequest>();
if (cacheHit == null) {
collectPutRequests(contexts.get(CacheableOperation.class), ExpressionEvaluator.NO_RESULT, cachePutRequests);
}
Cache.ValueWrapper result = null;
// If there are no put requests, just use the cache hit
if (cachePutRequests.isEmpty() && !hasCachePut(contexts)) {
result = cacheHit;
}
// Invoke the method if don't have a cache hit
if (result == null) {
result = new SimpleValueWrapper(invokeOperation(invoker));
}
// Collect any explicit #CachePuts
collectPutRequests(contexts.get(CachePutOperation.class), result.get(), cachePutRequests);
// Process any collected put requests, either from #CachePut or a #Cacheable miss
for (CachePutRequest cachePutRequest : cachePutRequests) {
cachePutRequest.apply(result.get());
}
// Process any late evictions
processCacheEvicts(contexts.get(CacheEvictOperation.class), false, result.get());
return result.get();
}
I think should prevent the cachePutRequest execute. if no cache be hit, to invoke the method body of #Cacheable and don't cached the result. use unless will prevent the method invoke. Is this correct?
#Tonney Bing
First of all, my apologies for misguiding you on my previous answer...
If condition evaluates to false, then the method will always be
executed and the result subsequently cached.
The last part is NOT true. In fact, the condition attribute does prevent the #Cacheable method result from being cached. But, neither the condition nor the unless attribute prevent the #Cacheable service method from being invoked.
Also, my code example above was not correct. The unless attribute needs to be set to true to prevent caching of the #Cacheable method result.
After re-reading this section in the Spring Reference Guide, I came to realize my mistake and wrote an example test class to verify Spring's "conditional" caching behavior.
So...
With respect to your business use case, the way I understand it based on your original question and subsequently, your response to my previous answer, you have a #Cacheable service method that needs to be suppressed of invocation in the read-only app regardless of whether the value is in the cache or not! In other words, the value should always be retrieved from the cache and the #Cacheable service method should NOT be invoked in read-only mode.
Now to avoid polluting your application code with Spring infrastructure component references, and specifically, with a Spring CacheManager, this is a good example of a "cross-cutting concern" (since multiple, mutating-based application service operations may exist) and therefore, can be handled appropriately using AOP.
I have coded such an example satisfying your requirements here.
This is a self-contained test class. The key characteristics of this test class include...
The use of external configuration (by way of the app.mode.read-only System property) to determine if the app is in read-only mode.
The use of AOP and a custom Aspect to control whether the subsequent invocation of the Joint Point (i.e. the #Cacheable service method) is allowed (no, in a read-only context). In addition, I appropriately set the order in which the Advice (namely, the #Cacheable based advice along with the handleReadOnlyMode advice in the UseCacheExclusivelyInReadOnlyModeAspect Aspect) should fire based on precedence.
Take note of the #Cacheable annotation on the service method...
#Cacheable(value = "Factorials", unless = "T(java.lang.System).getProperty('app.mode.read-only', 'false')")
public Long factorial(long number) { .. }
You can see the intended behavior with the System.err output statements in the test class.
Hope this helps!
Most sample codes around Reactive Extensions revolves around how you compose logic and operators on the sequence.
The parts around Observable generation focus around "FromEventPatter","FromAsynch" etc.
IObservable<string> observableHotStatus = ??;
foreach (var task in todo)
{
//Process task;
//Post status message into observable; How do I do this?
}
In short, I want an object that I can post into, like an ActionBlock, Action (of T) or something like that.
What's the easiest way to achieve this?
Edit:
Examining your code more closely, I'd recommend using Observable.Create. Even though it only returns a cold observable, you can apply the Publish operator to the generated observable to make it hot.
And if by task you're actually referring to Task<T>, then you can use an overload of Observable.Create that allows you to define an async iterator. For example:
IObservable<string> statuses = Observable.Create<string>(
(observer, cancel) =>
{
foreach (var task in todo)
{
cancel.ThrowIfCancellationRequested();
await task;
observer.OnNext("Status");
}
});
Previous Answer:
You could use one of the following types, but I suggest reading To Use Subject or Not To Use Subject first before making your decision.
Subject<T>: General purpose, "event"-like, hot observable. Calling OnNext is like raising a classic .NET event.
BehaviorSubject<T>: Generally used as the backing field for a property, it represents an observable sequence of change "events". Whenever an observer subscribes, it receives the current value immediately, followed by all changes to the property. You can extract the current value at any time from the Value property; e.g., within your property's getter. Call OnNext within your property's setter and you don't have to keep a duplicate backing field. It's also Rx's version of a continuous function and it's the only FRP-like thing you'll find in Rx, if my understanding of FRP is correct.
ReplaySubject<T>: Generally used as an historical buffer of "events", it represents an observable sequence of values beginning with the values that have been missed by an observer, whenever an observer subscribes. You can control how far back values are buffered; it's like a sliding window over the history of values. You rarely have to use this type. In most cases, the Observable.Replay operator will do.
AsyncSubject<T>: Generally used to capture the results of hot, asynchronous functions like Task<T>. You rarely have to use this type. In most cases, Observable.FromAsyncPattern or Task-conversion operators will do.
I am implementing my own Map in Java, using a custom class I made.
I already implemented the hashCode and equals without any problem.
I just have a question more related into performance and stuff like that.
So I will check many times in my application if a specific value is inside the map, for that, for that I have to create a object and then use the methods containsKey of Map.
My question is...
Is there any other way? without being always creating the object???
I cant have all the objects in my context universe, so that isn't a way...
I know I can just point the object to 'null' after using it, but still, it's not so elegant, creating objects just to check if there is the same object inside =S
Are there any other conventions?
Thank you very much in advance!
EDIT:
Stuff typed = new Stuff(stuff1, stuff2, (char) stuff3);
if(StuffWarehouse.containsKey(typed))
{
//do stuff
}
//after this I won't want to use that object again so...
typed = null;