is there any way to invoke a block with nil as a given argument, given that the invokeBlockWithArgs: requires the args to be nil-terminated?
example method definition in a mocked object:
- (void)methodWithCompletion:(void(^)(NSString*, NSError* )) completionBlock;
The given mockObject should call:
completionBlock(#"foo", nil);
however, with invokeBlockWithArgs:
OCMStub([mockObj methodWithCompletion:([OCMArg invokeBlockWithArgs:#"foo", nil, nil])]);
Method fails, with too few arguments; obviously with nil being the termination, it doesn't recognize the second parameter to the block should be nil.
I haven't tested it but theoretically passing [NSNull null] should work.
Adding to the existing answers here, passing [NSNull null] does what you want in this case, which is passing nil as the param there.
I had a case (shown below) where my logic tested the existence of an error object OR my array was empty, and wanted my test to cover both cases and was afraid I'd only be able to test one case
if (error || array.count == 0) {
// fail here
}
Here is my test OCMock code:
NSArray *emptyArray = #[];
OCMStub([requestMock loadListWithCompletion:([OCMArg invokeBlockWithArgs:emptyArray, [NSNull null], nil])]);
...and in the actual invocation of that method, the error param (that I passed [NSNull null] into) was indeed nil, so the logic fell through to the empty array and the error case was still handled.
You can pass [NSNull null]. I just tested, it works.
Related
I'm making an API server using GoLang and I am using Mux as the HTTP router. I have one endpoint in my app, /tasks. When I hit that endpoint, I get back an array of results, which is as expected. Now, I want to build upon that and add an optional query parameter into the URL to only return N results, like so: /tasks?num=5 which would only return 5 results. I have accomplished this using the handler below:
vars := r.URL.Query()
t := task{}
if numOfTasksParam, ok := vars["num"]; ok {
fmt.Printf("%+v", numOfTasksParam[0])
numOfTasks, err := strconv.Atoi(vars.Get("num"))
//return only n number of results
} else {
//return the entire result set
}
I devised this solution because I discovered that URL.Query() returns a map of the query parameters and therefore, I can just check to see if that map contained the key of "num". If so, the client wants N number of results. If not, the client must want the whole result set.
The main issue I have with this approach is that when I go to check if the keys exists, I make a temporary variable called numOfTasksParam which holds the query parameter value, but it holds the value as a string and I need a int. Therefore, I must use the numOfTasksParam somehow and then create another variable to convert that to an integer value.
Is there more succinct or convenient way of checking if a query parameter exists in the request URL?
This is probably the most succinct, and works because Get returns an empty string if the parameter isn't set, which Atoi will fail to parse:
vars := r.URL.Query()
t := task{}
if numOfTasks, err := strconv.Atoi(vars.Get("num")); err == nil {
//return only numOfTasks number of results
} else {
//return the entire result set
}
The price you pay for having less code is that if a user passes an invalid value like ?num=taco, it will be treated as if they passed nothing, rather than telling the user they passed something unusable. This may or may not be what you want. It is also slightly less efficient, because it will run Atoi even if the value is known to be empty.
I'm a Golang newbie but I thought I had got the essentials of pointers and references straight, but apparently not:
I have a method that must return a []github.Repository, which is a type from the Github client in go.
The API call returns the results paginated so I must cycle until there's no more results, and add the result of each call to the allRepos variable, and return that. Here's what I have so far:
func (s *inmemService) GetWatchedRepos(ctx context.Context, username string) ([]github.Repository, error) {
s.mtx.RLock()
defer s.mtx.RUnlock()
opt := &github.ListOptions{PerPage: 20}
var allRepos []github.Repository
for {
// repos is of type *[]github.Repository
repos, resp, err := s.ghClient.Activity.ListWatched(ctx, "", opt)
if err != nil {
return []github.Repository{}, err
}
// ERROR: Cannot use repos (type []*github.Repository) as type github.Repository
// but dereferencing it doesn't work, either
allRepos = append(allRepos, repos...)
if resp.NextPage == 0 {
break
}
opt.Page = resp.NextPage
}
return allRepos, nil
}
My question: how can I append the results of each call and return a result of type []github.Repository?
Also, why doesn't dereferencing work here? I've tried replacing allRepos = append(allRepos, repos...) with allRepos = append(allRepos, *(repos)...) but I get this error message:
Invalid indirect of (repos) (type []*github.Repository)
Well, something is not okay here:
You say in the comment that "repos is of type *[]github.Repository" but the compiler's error message indicates that repos is of type []*Repository". The compiler is never (except when buggy) wrong.
Note that *[]github.Repository and []*Repository are completely different types, especially the second is not a slice of Repositories and you cannot (really, there is no way) dereference these pointers during append(): You have to write a loop and dereference each slice item and append one by one.
What is strange too: github.Repository and Repository seem to be two different types one from package github, the other from the current package. Again, you'll have to get that straight too.
Note that there are no references in Go. Stop thinking about these immediately: This is a concept from other languages which is not helpful (as inexistent) in Go.
In your example the dereferencing is not correct. You should make it like this:
allRepos = append(allRepos, *repos...)
Here a simple example with dereferencing a pointer to a slice of string. https://play.golang.org/p/UDzaG5z8Pf
I am trying to download something from 3 servers. My idea is if the first server is closed,it will use the second server. I noticed,if the first server has been closed, it will created a run time error.I want to know how to use this error,what i need is like this:
if run time err!=nil{do something}
i am new to golang,hope someone can help me
thank you
To elaborate on what FUZxxl explained, go makes a distinction between an error (something which could go wrong indeed went wrong) and an exception (something which could not possibly go wrong actually went wrong).
The distinction can sometimes be subtle (as it relies on what is 'unexpected'), but it can also be clearer than the 'everything is an exception' that you see in other languages.
For instance, consider integers which might overflow. One possibility is to consider it a 'normal' behaviour, which should be handled appropriately:
func safe_add(x, y uint32) (uint32, error) {
z := x + y
if z < x || z < y {
return 0, fmt.Errorf("Integer overflow")
}
return z, nil
}
Another is to consider it 'never happens' and have the runtime panic in the unlikely case when it happens against all odds:
func panic_add(x, y uint32) uint32 {
z, err := safe_add(x, y)
if err != nil {
panic(err)
}
return z
}
(Note that I use my own 'safe_add' here, but you don't have to of course)
The main difference is in the way you handle the error afterwards. Adding a number to itself until it overflows with errors gives:
func safeloop(u uint32) {
var err error
for {
if u, err = safe_add(u, u); err != nil {
fmt.Println(err)
return
} else {
fmt.Println(u)
}
}
}
While handling panics uses the recover built-in function:
func panicloop(u uint32) {
defer func() {
if err := recover(); err != nil {
fmt.Println(err)
}
}()
for {
u = panic_add(u, u)
fmt.Println(u)
}
}
(full examples on the playground)
Note that the panic version has a much simpler loop, as you basically never expect anything to go wrong and never check for errors. The counterpart for this is that the way to handle panics is quite cumbersome, even for a very simple example like this. You defer a function which will call recover and capture the error when it arises and breaks out of the function. When your code becomes more complex, tracking exactly where/how the panic arose and acting on it accordingly can become much more complex than checking for errors in places where they could arise, with the result, err := func_which_may_fail(...) pattern.
You can even alternate between panics, recover which return errors, errors converted to panics, ... but this is (understandably) considered poor design.
There are some good resources on error handling and panics on the go blog. The specs is a good read to.
In your case, as you expect 'the server is closed' to be a pretty frequent behaviour, you should definitely go the error way, as FUZxxl suggested, but I hope this might be useful to you (or others) to understand how error handling works in Go.
When you do something which could go wrong, you get an error object.
bytes, err = stream.Read(buffer)
To check whether what you tried actually went wrong, compare the error object against nil. nil signalizes that no error has happened. In the case the error is not nil, you can do something about it.
if err != nil {
// insert error handling here
}
Correction:
Link #1 http://play.golang.org/p/CKRNyWYF8X
Link #2 http://play.golang.org/p/oT2yKzFwep
From the first link,
I am sure that the panic error comes from this
func (A *DoublyLinkedList) AddHead(input_value interface{}) {
temp_node := &Node{value: input_value, prev: nil, next: A.head}
original_head_node := A.head
original_head_node.prev = temp_node
A.length++
}
But when I use this for doubly linked list, it panics little later. And still fails because this one below does not connect the original head with previous pointer.
func (A *DoublyLinkedList) AddHead(input_value interface{}) {
A.head = NewNode(input_value, nil, A.head)
A.length++
}
This is the one. This one has the similar problem.
cannot assign to target_node.GetPrevNode().GetNextNode()
Does go not support pointer reference this way? I did fix this just assigning a new variable every time I need to get the pointer. But my first question on the top still does not compile.
In short, how do I connect the doubly linked list when adding a new element in Go?
You need to initialize the properties inside the DoublyLinkedList. It seems to me, you are currently creating a reference to it in NewDoublyLinkedList() with 2 nil properties.
type DoublyLinkedList struct {
head *Node // nil
tail *Node // nil
length int
}
And when doing this
original_head_node := A.head // A.head == nil
original_head_node.prev = temp_node // You are trying to access a property in nil
I'm currently getting desperate over the behaviour of golangs reflect package, which to me doesn't seem consistent at all.
1) As far as I understand it, a reflect.Value seems to carry a pointer to the underlying value.
E.g. if I call
var s string
v1 := reflect.ValueOf(&s).Elem()
v2 := v1
v2.SetString("Hello World!")
fmt.Println(s)
It prints me "Hello World!".
However, this doesn't seem to hold true for a reflect.Value obtained by a call to Field().
val := ... //Assign a reflect.Value to it
nextval := val.Field(0) //Make sure that Field exists and is of type map
nextval = reflect.MakeMap(reflect.MapOf(KEY, ELEM))
nextval.SetMapIndex(Some_value_of_type_KEY, Something_of_type_ELEM)
fmt.Println(nextval.MapKeys()
fmt.Println(val.Field(index).MapKeys())
This prints
[Some_value_of_type_KEY]
[]
which is a major annoyance. Anyone knows why this is the case?
===================================================
2) Consider the function
func Test(v interface{}) {
val := reflect.ValueOf(v)
if val.Kind() != reflect.Struct {
fmt.Println("It is a struct")
}
}
If I call it with any struct as an argument it prints "This is a struct".
However, I won't be able to assign new values to stuff inside v by using val,
due to the value not being addressable. Working around by the following:
func Test(v interface{}) {
val := reflect.ValueOf(&v).Elem()
if val.Kind() != reflect.Struct {
fmt.Println("This never get's printed!")
}
}
According to the doc, I would assume, that by taking the '&' I use a pointer to v and by the call of Elem() I get the element it points to, therefore val.Kind() should still return the same thing. It doesn't. val.Kind() now is a reflect.Interface.
Is there a way of not having to go
valForTestingKind := reflect.ValueOf(v)
valForSettingNewValue := reflect.ValueOf(&v).Elem()
as this somehow feels wrong.
Part 1:
By assigning to nextval, you are breaking its association with the original val. Instead, use the Set() method.
nextval.Set(reflect.MakeMap(reflect.MapOf(KEY, ELEM)))
Set() is the equivalent of assignment in the reflection world. Of course, you must make sure it is assignable using reflect.ValueOf(&v).Elem() as you do in your first code example.
Part 2:
The issue here is that you have another level of indirection. v is of type interface{} and has a concrete value whose type is of Kind struct. Just like with every function that accepts an interface typed parameter, when you call reflect.ValueOf, the parameter is automatically converted to that type. However, converting an interface to another interface results in the concrete value being reboxed in the new interface type. The information of the type before it was reboxed is lost. As an example, a function that accepts an io.Writer would not know that the calling function considered it an io.ReaderWriter.
In this context, it means that reflect.ValueOf cannot tell if you passed an os.File (some struct) or a file boxed in an interface{}. It assumes you passed an os.File and shows you the Kind "struct".
However, when you pass a pointer to an interface{}, you are passing an interface{} variable that can be modified. You are not passing the underlying concrete type and that has important consequences. You can .Set() anything, not just what the original concrete type allows. You also can't edit individual fields as anything in an interface{} is not assignable. If the concrete type is in fact a pointer, you can do a fourth dereference (.Elem()) and modify fields from there.
So, what does this mean in terms of code?
//let v = an interface{} with a concrete type of SomeStruct
val := reflect.ValueOf(&v).Elem()
fmt.Println(val.Elem().Kind()) // struct
val.Elem().Field(0).Set(10) // PANIC! Field isn't assignable.
val.Set("a string which is not a SomeStruct")
fmt.Println(val.Elem().Kind()) // string
I made an example here: http://play.golang.org/p/6MULn3KoNh
I want to talk about your second block of code:
val := ... //Assign a reflect.Value to it
nextval := val.Field(0) //Make sure that Field exists and is of type map
nextval = reflect.MakeMap(reflect.MapOf(KEY, ELEM))
nextval.SetMapIndex(Some_value_of_type_KEY, Something_of_type_ELEM)
fmt.Println(nextval.MapKeys()
fmt.Println(val.Field(index).MapKeys())
On the third line, you are reassigning a new, different object to the variable nextval. Shouldn't you call some kind of setting method on nextval instead of reassigning it? In your first example, you called SetString but in this example you are just reassigning the variable and that might be why the behavior is different. After you reassign the variable, nextval will no longer be connected in any way to val.Field(0). Also, what is index?
If this does not explain your problem, please edit the question to contain a short, self-contained, correct, compilable example ( SSCCE ). I want to be able to post it into the text box on the front page of golang.org in order to see the problem. You should always post an SSCCE when possible.
You have not shown a complete and compilable code. Do you pass a pointer to a struct or do you pass the struct by value? In the later case reflection cannot mutate it.
Values stored in a map are not addressable even when not using reflection.
http://play.golang.org/p/wYLeJ3W4R2
http://play.golang.org/p/ttUGBVh1lc
https://groups.google.com/forum/#!topic/golang-nuts/jzjEXoc9FwU
https://groups.google.com/forum/#!topic/golang-nuts/V_5kwzwKJAY