assignment to entry in nil map nested map

Example error:

This panic occurs when you fail to initialize a map properly.

Initial Steps Overview

• Check the declaration of the map

Detailed Steps

1) check the declaration of the map.

If necessary, use the error information to locate the map causing the issue, then find where this map is first declared, which may be as below:

The block of code above specifies the kind of map we want ( string: int ), but doesn’t actually create a map for us to use. This will cause a panic when we try to assign values to the map. Instead you should use the make keyword as outlined in Solution A . If you are trying to create a series of nested maps (a map similar to a JSON structure, for example), see Solution B .

Solutions List

A) use ‘make’ to initialize the map.

B) Nested maps

Solutions Detail

Instead, we can use make to initialize a map of the specified type. We’re then free to set and retrieve key:value pairs in the map as usual.

B) Nested Maps

If you are trying to use a map within another map, for example when building JSON-like data, things can become more complicated, but the same principles remain in that make is required to initialize a map.

For a more convenient way to work with this kind of nested structure see Further Step 1 . It may also be worth considering using Go structs or the Go JSON package .

Further Steps

• Use composite literals to create map in-line

1) Use composite literals to create map in-line

Using a composite literal we can skip having to use the make keyword and reduce the required number of lines of code.

Further Information

https://yourbasic.org/golang/gotcha-assignment-entry-nil-map/ https://stackoverflow.com/questions/35379378/go-assignment-to-entry-in-nil-map https://stackoverflow.com/questions/27267900/runtime-error-assignment-to-entry-in-nil-map

Map is apparently nil even though I already assigned to it

Go version: 1.12.2 Error text: panic: assignment to entry in nil map

I’m aware that assigning to just a var myMap map[string]int leads to an issue with assignment to a nil map and that you have to do myMap := make(map[string]int) but I seem to be having the same issue with a map that I’ve already assigned to. Below is the stripped down code. Beware that I’ve added a bunch of superfluous stuff as a means of troubleshooting (though I tried to rip a lot of that out):

I added “tmpRect” in an attempt to make sure that detMap is actually not nil. ImageFrames.Sublimate() is below:

I get the same issue if I just do tmpImg, _, _, _, detMap, sublError := imageFrames.Sublimate(frm) without creating the map beforehand.

Hi @ashinnv Try to send the current value of the frm to the goroutine. Example:

Or replace “input[i]” with the variable “i”. Otherwise maybe you have a concurrency problem.

Which line here is that panic coming from? That should indicate which line has the map access where the map is nil.

Which line?

I tried that but still ended up with the same error. I’ve re-written the function to include the lines from Sublimate(), but I’m still getting the issue. I completely removed the anonymous function, as well, so that this is now just a serial loop with just an input chan and an output chan. The new, unstripped version is below:

This is just weird. I’m sure it’s some stupid little thing I’m completely overlooking, but still, geez.

The issue was coming from creating the “Frame” type. I create them in a completely different process from images taken from the webcam. These are then encoded and transmitted down a pipeline. When I originally created the Frame type, I created a function that spits out a new frame to be used across the whole project for when I want to create frames, but at this time, I didn’t have the map of opencv detections included.

When I added computer vision to the project, I didn’t update the function that creates blank frames, instead only adding the struct element. This meant that following that, all new frames that were created would have a nil element where the detection map should be.

That frame with a nil detection map would be encoded and sent down the pipeline, where it caused problems in this process. Thanks for all the help and suggestions, guys.

Is this nil? You create retMap in the Sublimate function, but then overwrite it with whatever is in inFrm.Detections and then return that.

EDIT : Oops. I missed that you found out already. Never mind!

That came from the thrashing I’d given the source in trying to figure out what was going on. I kept adding and removing stuff in an attempt to get an idea of where the issue was happening. Never considered it wasn’t even in this process at all.

HatchJS.com

Cracking the Shell of Mystery

Panic: Assignment to Entry in Nil Map

Maps are a powerful tool in Golang, but they can also be a source of confusion and frustration. One common error that Golang programmers make is trying to assign a value to an entry in a nil map. This will cause a panic, which is a fatal error that terminates the program.

In this article, we’ll take a look at what a nil map is, why it’s dangerous to assign values to them, and how to avoid this error. We’ll also provide some tips on how to debug panics caused by nil maps.

What is a Nil Map?

A nil map is a map that has not been initialized. This means that it has no entries, and it cannot be used to store or retrieve data.

When you try to access an entry in a nil map, you will get a panic. This is because the compiler cannot guarantee that the map will ever contain any entries, so it cannot safely perform the operation.

Why is it Dangerous to Assign Values to Nil Maps?

Assigning values to nil maps is dangerous because it can lead to unexpected behavior and errors. For example, if you try to assign a value to a nil map, the compiler will not check to see if the map exists. This means that you could accidentally overwrite a valid map with a nil map, which could corrupt your data.

How to Avoid This Error

There are a few ways to avoid the error of assigning values to nil maps.

• Always check to see if a map is nil before you try to access or modify it. You can do this using the `len()` function. If the length of the map is 0, then it is nil.
• Use the `make()` function to create a new map. This will ensure that the map is initialized and that you can safely assign values to it.
• Use the `delete()` function to remove entries from a map. This will prevent you from accidentally overwriting a valid map with a nil map.

Tips for Debugging Panics Caused by Nil Maps

If you get a panic caused by a nil map, here are a few tips for debugging the problem:

• Check the stack trace. The stack trace will show you the line of code where the panic occurred. This can help you identify the source of the error.
• Use the `print()` function to print the values of your maps. This can help you see if there are any nil maps in your code.
• Use the `debug` package to set breakpoints and inspect your code. This can help you track down the problem and fix it.

Nil maps can be a source of confusion and frustration, but they can also be avoided by following a few simple guidelines. By checking for nil maps before you access or modify them, using the `make()` function to create new maps, and using the `delete()` function to remove entries from maps, you can prevent yourself from getting the panic: assignment to entry in nil map error.

What is a panic?

A panic is a sudden, unexpected crash of a computer program. It can be caused by a variety of errors, such as a divide-by-zero error, an invalid memory access, or a runtime error. When a panic occurs, the program terminates immediately and the operating system displays an error message.

Panics are usually caused by programming errors. However, they can also be caused by hardware problems, such as a faulty memory chip. If you are experiencing frequent panics, it is a good idea to check your hardware for problems.

What is a nil map?

A nil map is a map that has no entries. In other words, it is a map with a size of zero. Nil maps are often used as default values for maps that are not yet initialized.

You can create a nil map using the following code:

map := make(map[string]int)

You can also check if a map is nil using the following code:

if map == nil { // The map is nil. }

Nil maps are not the same as empty maps. An empty map is a map that has been initialized, but does not have any entries. You can create an empty map using the following code:

map := map[string]int{}

You can check if a map is empty using the following code:

if len(map) == 0 { // The map is empty. }

Panics are a common problem in computer programming. They can be caused by a variety of errors, such as programming errors, hardware problems, or operating system problems. Nil maps are a special type of map that has no entries. They are often used as default values for maps that are not yet initialized.

What causes the panic `assignment to entry in nil map`?

The panic `assignment to entry in nil map` occurs when you try to assign a value to a key in a map that does not exist. This can happen when you are using a map literal to initialize a variable, or when you are using the `map.insert()` method to add a new key-value pair to a map.

For example, the following code will cause a panic:

var m map[string]int m[“foo”] = 10

This is because the map `m` is nil, which means that it does not have any key-value pairs. When you try to assign a value to the key `”foo”`, the compiler will panic because there is no entry in the map to assign the value to.

You can avoid this panic by checking to see if the map exists before you try to assign a value to it. You can do this using the `len()` function, which returns the number of key-value pairs in a map. If the map is empty, you can use the `map.default()` method to set a default value for the key.

For example, the following code will not cause a panic:

var m map[string]int if len(m) == 0 { m = make(map[string]int) } m[“foo”] = 10

How to avoid the panic `assignment to entry in nil map`?

There are a few ways to avoid the panic `assignment to entry in nil map`.

• Check to see if the map exists before you try to assign a value to it. You can do this using the `len()` function, which returns the number of key-value pairs in a map. If the map is empty, you can use the `map.default()` method to set a default value for the key.
• Use the `make()` function to create a new map. This will ensure that the map is not nil, and you will not get a panic when you try to assign a value to it.
• Use the `map.delete()` method to remove a key from the map before you try to assign a value to it. This will ensure that the key does not exist in the map, and you will not get a panic when you try to assign a value to it.

Here are some examples of how to avoid the panic `assignment to entry in nil map`:

// Check to see if the map exists before you try to assign a value to it. var m map[string]int if len(m) == 0 { m = make(map[string]int) } m[“foo”] = 10

// Use the `make()` function to create a new map. m := make(map[string]int) m[“foo”] = 10

// Use the `map.delete()` method to remove a key from the map before you try to assign a value to it. m := make(map[string]int) m[“foo”] = 10 delete(m, “foo”) m[“foo”] = 20

By following these tips, you can avoid the panic `assignment to entry in nil map` and ensure that your code is more reliable.

Q: What does the error “panic: assignment to entry in nil map” mean?

A: This error occurs when you try to access or modify a value in a map that does not exist. This can happen if you accidentally mistype the key, or if the map has been cleared.

Q: How can I fix the error “panic: assignment to entry in nil map”?

A: There are a few ways to fix this error.

• Make sure the key you are using exists. If you are not sure whether the key exists, you can use the `len()` function to check the length of the map. If the length is 0, then the key does not exist.
• Clear the map before trying to access it. If you know that the key exists, but the map has been cleared, you can clear the map before trying to access it. You can do this by calling the `clear()` method on the map.
• Use the `default()` method to get a default value for the key. If you do not want to check whether the key exists, you can use the `default()` method to get a default value for the key. The `default()` method takes a function as an argument. The function will be called if the key does not exist. The function should return the default value for the key.

Q: What are some common causes of the error “panic: assignment to entry in nil map”?

A: There are a few common causes of this error.

• Mistyping the key. This is the most common cause of the error. Make sure you are typing the key correctly.
• Clearing the map. If you clear the map, all of the keys and values will be removed. This means that any attempts to access or modify a value in the map will result in an error.
• Using the wrong type of key. The keys in a map must be of a type that can be used as an index. This means that they must be a string, a number, or a pointer to a struct. If you try to use a key of a different type, you will get an error.

Q: What can I do to prevent the error “panic: assignment to entry in nil map”?

A: There are a few things you can do to prevent this error.

• Be careful when typing keys. Make sure you are typing the keys correctly.
• Clear the map before trying to access it. If you know that the map has been cleared, clear it before trying to access it.
• Use the `default()` method to get a default value for the key. If you do not want to check whether the key exists, you can use the `default()` method to get a default value for the key.

Q: What are the security implications of the error “panic: assignment to entry in nil map”?

A: This error can have security implications if it is not handled properly. If an attacker can exploit this error, they could gain access to sensitive data or even execute arbitrary code. It is important to make sure that this error is handled properly in order to protect your application from security breaches.

In this blog post, we discussed the error panic: assignment to entry in nil map. We explained what this error means and how it can be avoided. We also provided some tips for debugging this error.

We hope that this blog post has been helpful. If you have any other questions about this error, please feel free to contact us.

Here are some key takeaways from this blog post:

• The panic: assignment to entry in nil map error occurs when you try to access a key in a map that does not exist.
• This error can be avoided by checking to make sure that the map exists before you try to access it.
• You can debug this error by using the following steps:
• Check to make sure that the map exists.
• Check to make sure that the key you are trying to access exists.
• Check to make sure that you are using the correct syntax to access the map.

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Go gotcha: Why can't I add elements to my map?

Why does this code give a run-time error?

You have to initialize the map using the make function before you can add any elements:

Golang Tutorial

Golang reference, beego framework, golang error assignment to entry in nil map.

Map types are reference types, like pointers or slices, and so the value of rect is nil ; it doesn't point to an initialized map. A nil map behaves like an empty map when reading, but attempts to write to a nil map will cause a runtime panic; don't do that.

What do you think will be the output of the following program?

The Zero Value of an uninitialized map is nil. Both len and accessing the value of rect["height"] will work on nil map. len returns 0 and the key of "height" is not found in map and you will get back zero value for int which is 0. Similarly, idx will return 0 and key will return false.

You can also make a map and set its initial value with curly brackets {}.

Most Helpful This Week

Assignment to entry in nil map

Why does this program panic?

You have to initialize the map using the make function (or a map literal) before you can add any elements:

See Maps explained for more about maps.

Nested Maps in Go

I recently had to use a bunch of nested maps in Go and struggled way too long to get them “working”. And obviously there wasn’t a lot of good information to be found via $popular_search_engine. So i thought this might make a good blog post.

What gave me the proper nudge in the correct direction of thinking correctly was a Google Groups posting from 2012: https://groups.google.com/g/golang-nuts/c/PoRkoN84KKU/m/7330L9NulHQJ

You need to actually initialize every inner map seperatly if you want to use it! For more details you should read the rest ;-)

A simple example and the attempt of an explaination

Lets create a simple example to demonstrate the issue at hand:

Now open nested_maps.go in your favorite editor and paste in the following piece of code:

What we try to do here:

is to put a JSON array, where each array element contains three key-value pairs that define a group name, the persons name and their age, into a nested map. The intention for this might be that we think processing the data via a nested map is nice. Or whatever.

While this compiles perfectly fine, running the created binary will result in this runtime error:

My n00bish reaction at first was “WTF? I created the map with make() . It’s not nil!” But obviously i was terribly wrong.

What happens here is that Go creates the outer map but nothing else. And this makes perfect sense since it can’t possibly know how many inner maps we might want later on. It’s our job to take care of that.

A solution for that is extending our for loop like this:

The comments hopefully speak for themselves, but anyways: What we added is a simple check if the inner map to which we want write data already exists. This is done with a simple map lookup, which in Go returns not only the potential value but also a boolean value on which we can do a simple check with if . So if we get a false back, we just create the inner map with a make() and all is good.

Here is the full example which executes without a runtime error:

Hope this helps somebody else at some point in the future :-)

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`panic: assignment to entry in nil map` at nested maps

this code giving err panic: assignment to entry in nil map

is anything wrong in implementing the maps? i want to create a map key like 1,2,3.... like this, so imeplemented [string(rune(id+1))] now it giving error atfter implementing this one.

i want to create a map to convert it into json like this:

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Panic: assignment to entry in nil map

When doing docker login in the command prompt / powershell, I the error posted below. Though when doing this, docker desktop gets logged in just fine.

login Authenticating with existing credentials… panic: assignment to entry in nil map

goroutine 1 [running]: github.com/docker/cli/cli/config/credentials.(*fileStore).Store (0xc0004d32c0, {{0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}, {0x149b9b7, …}, …})

Although powershell is available for Linux and macOS as well, I assume you installed Docker Desktop on Windows, right?

I thing so because I have the same problem and I certainly installed on Windows… Do you have a solution? QVQ

I believe I’m experiencing the same issue - new laptop, new docker desktop for windows install. can’t login via command line:

goroutine 1 [running]: github.com/docker/cli/cli/config/credentials.(*fileStore).Store (0xc0004d4600, {{0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}, {0x0, 0x0}, {0xc00003c420, …}, …}) /go/src/github.com/docker/cli/cli/config/credentials/file_store.go:55 +0x49

I’m experiencing the same issue with my new windows laptop with fresh installation of docker.

Sorry, shortly after posting, I came to think about this very important info. You are of course absolutely correct. This is on a freshly installed Windows 11, latest docker-desktop.

I could try, if wanted. To do a fresh install on a Linux box and see if I experience the same issue there?

I have the same issue, works for me when I use WT and ubuntu, but not from cmd, git bash or powershell

If it is not a problem for you, that coud help to find out if it is only a Windows issue, but since so many of you had the same issue on the same day, it is very likely to be a bug. Can you share this issue on GitHub?

I tried it on my Windows even though I don’t use Docker Desktop on Windows only when I try to help someone, and it worked for me but it doesn’t mean that it’s not a bug.

If you report the bug on GitHub and share the link here, everyone can join the conversation there too.

In the meantime everyone could try to rename the .docker folder in the \Users\USERNAME folder and try the docke rlogin command again. If the error was something in that folder, that can fix it, but even if it is the case, it shouldn’t have happened.

you cloud try to run docker logout and then docker login ,it works for me .

That’s a good idea too.

I can verify that this did help on my PC too. I have created en issue here:

Hi all, a fix for this will be tracked on the docker/cli issue tracker: Nil pointer dereference on loading the config file · Issue #4414 · docker/cli · GitHub

I was using “az acr login” to do an azure registry docker login and getting this error, but I followed your advice and did a “docker logout” and that cleaned up my issue.

worked for my on my box (latest docker - Docker version 24.0.2, build cb74dfc) on W11. thx for solution.

its work for me. Recommend!

This solution works for me

“docker logout” works for me. Thank you!

Logout worked here too!

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assignment to entry in nil map

I am trying to assign values to a map that is initialized in the init func.

But panic occurs: assignment to entry in nil map

https://play.golang.org/p/yOwXzDkWIo

• instantiation

2 Answers 2

The function takes Test as value, so it gets its own copy of it. All changes to test Test will be gone when the function returns. Take Test by pointer instead:

Note though, the struct Test is exported, the method init is not, therefore a user of your library could potentially create a Test but not init it properly. It seems like the go community has established the convention of a freestanding NewType method:

This ensures a user can only obtain a test by calling NewTest and it will be initialized as intended.

• Makes total sense, i can't believe I didnt realize this myself. Thanks for the answer and the extra pair of eyes. –  TjeerdJan Commented Aug 21, 2016 at 12:39

You should use a pointer receiver for the init method:

Without a pointer, you are initializing a map for a copy of the test object. The actual test object never gets an initialized map.

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不要向nil map写入(panic: assignment to entry in nil map) #7

kevinyan815 commented Aug 4, 2019 • edited Loading

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fanyingjie11 commented Apr 25, 2022

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kevinyan815 commented Apr 29, 2022

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