TL;DR map[]struct{} is 5% faster in time and 10% less memory consumption comparing to map[]bool when it comes to a big Set.. How to return dictionary keys as a list in Python? Why are all android web browsers unable to display PDF documents? For example, you might store some extra per-request data in a web server in a map[*http.Request]string or something. Here the sample is a map that has a string as key and int type as the value. rev2022.11.22.43050. But, what would you do? Teaching the difference between "you" and "me". (^o^). First: We create 3 structs and add them all as keys in the "storage" map. type UserID int userIDs := make(map[string]UserID) Requirements change and it must now use a combination of two strings as the key. type A struct { a1 int a2 string } type B struct { b1 int b2 string } type C struct { c1 int c2 string } there are 3 structs, I want put the names into a map as key, and process func as map value (instead of type-switch) input arg is a interface, use for loop to judge what struct this interface is. TQFP and VQFN on same footprint: good idea or bad? input arg is a interface, use for loop to judge what struct this interface is. Go Play: Run it yourself here This will not yield the expected behavior. It is a reference to a hash table. Why can't I drive a 12'' screw into 6x6 landscape timber? how to handle pointer to struct as key? Why didn't the US and allies supply Ukraine with air defense systems before the October strikes? Use map to implement Set means that the value of the map is not important, we only need to focus on the existence of the key. Output $ go run main.go Field: FirstName Value: John Field: Lastname Value: Doe Field: Email Value: johndoe@gmail.com Field: Phone Value: 1234567 Using golang for loop with Maps. E.g. However these are assumptions. Examples of those are out of scope for this post. Why are there no snow chains for bicycles? Print the map. If you do create a benchmark, please post results here, I'd like to see them. This is my first benchmark test therefore can be incorrect, please let me know if my test is leading incorrect result. The "structs" key in the struct's field tag value is the key name. make (map [type of key]type of value) employeeSalary := make(map[string]int) The above line of code creates a map named employeeSalary which has string keys and int values. Add global no traverse type to the list or use notraverse option in the struct field. There are valid cases where use of pointers as map keys is desirable and A named struct is any struct whose name has been declared before. IMHO using a struct is more elegant, and you'll get that performance back if you ever need to access the two field in the key. License Not the answer you're looking for? Should I pick a time if a professor asks me to? 1. type Food struct {} // Food is the name. package main import ( "encoding/json" "fmt" ) type MyStruct struct { Name string Score . Took a shot at benchmarking (This would be a good fit for a benchmark with sub-benchmarks). Find centralized, trusted content and collaborate around the technologies you use most. Back then, I always use a map with bool key. Does the speed bonus from the monk feature Unarmored Movement stack with the bonus from the barbarian feature Fast Movement? The map does not recognize this numeric value so it will return the This form can be used with other packages that operate on such data structures and also directly with the standard json package. The Go structure can be arbitrarily complex, containing slices, other structs, etc. If you want to be sure, why not implement both and benchmark them. The second &Name{..} expression has a different memory address. . This is true for use of sync.Map as well. A field in this struct is supposed to be a map also and this seems to go against the documentation provided here which says that only structs that have fields that can be compared with == and != can be in the fields of structs that are used as keys in maps. We will see how we create and use them. Edit; also, who knows what the complier+hardware is doing to the sting concat that's reused over and over. You can access the key:value pair of a Map using key. I was looking into using structs as keys in golang maps. Key in a Map acts like an index in an Array. I however went ahead to try the following: Is an atomic nucleus dense enough to cause significant bending of the spacetime? By accepting all cookies, you agree to our use of cookies to deliver and maintain our services and site, improve the quality of Reddit, personalize Reddit content and advertising, and measure the effectiveness of advertising. When the migration is complete, you will access your Teams at stackoverflowteams.com, and they will no longer appear in the left sidebar on stackoverflow.com. type Employee . I however went ahead to try the following: This seems to go against the documentation as a field in the struct used as a key is a map. However, my article could be a light topic and just come in short. What is the significance of the intersection in the analemma? Can a 14 AWG pigtail be used with a smart switch with a 20 amp breaker? This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. Might be optimised in a way real data wouldn't be. To review, open the file in an editor that reveals hidden Unicode characters. Is it safe to start using seasoned cast iron grill/griddle after 7 years? Employee. Press question mark to learn the rest of the keyboard shortcuts. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Not the answer you're looking for? Golang Maps. IMO if someone wanted to do a valid benchmark comparison they'd need to compare against something that worked in all the same cases, e.g. strings and using that as the key. Create struct instance. Outside the technical definition, what is the term "Pharisee" synomynous with inside Christian Teachings? package fixed_ttl_map import ("sync" "time") type TTLMap struct {ttl time.Duration // time-to-live interval time.Duration // intervals between each checks for expiry // internal variables m sync.Map c chan expireEvent} type wrappedValue struct {value interface{} expiry time.Time} func NewTTLMap() *TTLMap {m := &TTLMap{ttl: 1 * time.Minute, Instantly share code, notes, and snippets. And process this arg by process func in map value. zero-value of UserID. Golang Maps is a collection of unordered pairs of key-value. Create and initialize the map with struct as keys e.g. Not only will hashing a struct be faster than computing an md5 and hashing that, the storage space per key will be smaller as well. Go Map In Go, Map is a collection of unordered key:value pairs. 2. Stack Overflow for Teams is moving to its own domain! Pointers can be compared for equality even when the items they point to can't be compared. Get or Set by individual field name on struct. Making statements based on opinion; back them up with references or personal experience. The value for each is "true." How to increment a value in a function in Powershell? Golang React JS. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Sun light takes 1,000/30,000/100,000/170,000/1,000,000 years bouncing around inside to then reach the Earth. // Notice: We are using value of `A`, not `*A`, // Notice: We are using pointer of `*A`, not `A`. I can think of only 2 options, and currently, I chose to go with struct. Example. only comparable type can be used as a key (== ,!=). struct (not a pointer) is comparable in case it contains only comparable types. It is widely used because it provides fast lookups and values that can retrieve, update or delete with the help of keys. For example, this map of maps could be used to tally web page hits by country: hits := make(map[string]map[string]int) This is map of string to (map of string to . neither simple concatenation nor naive concatenation hashing will have the correct semantics for arbitrary input). We begin with a map of string keys and string valuesit contains some common vocabulary words. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Ask questions and post articles about the Go programming language and related tools, events etc. How do medical SMPS achieve lower Earth leakage compared to "regular" AC-DC SMPS? Go maps are one of the useful data structures and in computer science at large. For example, consider a map originally keyed on strings. Range Hood Galvanized Pipe - Installation Code. The problem here was unintentional use of pointers as map keys. Thanks for contributing an answer to Stack Overflow! Either insert keys when initializing or use index syntax to initialize. To build a golang map of struct, follow the below steps: Create a structure e.g. Keeping TCP Connections Alive in Golang . I want to share my experience and opinion about using empty struct in Golang. what about Edge{"from,foo", "to"} and Edge{"from", "foo,to"}. In Go language, a map is a powerful, ingenious, and versatile data structure. Connect and share knowledge within a single location that is structured and easy to search. Reddit and its partners use cookies and similar technologies to provide you with a better experience. Note: Per recommendation, I ran some test. Hashing and concatenating the two parts would not be easier or faster, since the Go runtime will hash the key anyway. Use the struct, because it's the simplest and most intuitive way to model your domain. The map uses pointers to struct values for its keys. Get struct field reflect.Kind by field name. mapkey-valuemapsetvalue. We can get values associated with keys from a map using index notation as shown below. The map uses pointers for its keys. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Get all reflect.StructField for given struct instance. Did Jean-Baptiste Mouron serve 100 years of jail time - and lived to be free again? To match on the values of the fields of the Name struct, use the Declaration To declare a Map, we may use map keyword along with the datatypes of key and value. Using reflect, how do you set the value of a struct field? Charity say that donation is matched: how does this work? The created struct should implement the golang sort . Example: How do medical SMPS achieve lower Earth leakage compared to "regular" AC-DC SMPS? https://blog.golang.org/go-maps-in-action, and check out the Key types section. Will use struct. A mistake that is easy to make with Go maps is unintentional use of pointers as map keys. Learn more about bidirectional Unicode characters. Short Story About a Woman Saving up to Buy a Gift? Keys: We get the keys from the map by using "range" and appending to an empty slice with append(). Please not that the square brackets are mandatory around the key . These structs should be compared with each other. How to print struct variables in console? rev2022.11.22.43050. return out. A struct can be used as the key of a map. question, would there be cases where its plausible to have a map's key to be pointer of x type? Maps are unordered collections, and there's no way to predict the order in which the key/value pairs will be returned. This method uses the "comma ok" pattern to determine if the map has a key named name.If it does, the ok value will be true; if not, the ok value will be false.This pattern makes our code safe . In maps, most of the data types can be used as a key like int, string, float64, rune, etc. You signed in with another tab or window. The below code snippet declares a struct type MyStruct with fields Name and Score. I expect that the struct is indeed faster. struct {}struct . The best approach is to create a struct of key and value properties. intentional. When the migration is complete, you will access your Teams at stackoverflowteams.com, and they will no longer appear in the left sidebar on stackoverflow.com. golang struct. This is commonly accomplished by introducing a struct that holds . Stack Overflow for Teams is moving to its own domain! https://blog.golang.org/go-maps-in-action. Golang: Using structs as key for Maps Raw struct_as_map_key.go This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. setmapset. Should I pick a time if a professor asks me to? I was looking into using structs as keys in golang maps. Short Story About a Woman Saving up to Buy a Gift? Structs with Maps. and the decoder will properly decode nested maps and so on into the proper structures . Clone with Git or checkout with SVN using the repositorys web address. If your program is too slow, profile it to see if map access is a bottleneck. A key works like an index, pointing to the value you associate with that key. Range Hood Galvanized Pipe - Installation Code. A wrong answer really, really fast is still wrong. By rejecting non-essential cookies, Reddit may still use certain cookies to ensure the proper functionality of our platform. 286. struct type name underlying-type. Do restaurants in Japan provide knife and fork? What is the purpose of defining a preprocessor macro like __BASH_H__ that is only used before it's set? Get all the struct field tags ( reflect.StructTag) or selectively by field name. In the last tutorial, we have talked about How to create a map & other basic things related to it in Golang.. So, it can be initialized using its name. It's obvious that strings, ints, and other basic types should be available as map keys, but perhaps unexpected are struct keys. Sorting by value is a little more complicated. Asking for help, clarification, or responding to other answers. 2. what can instead be used to access the keys in maps can be. 508), Why writing by hand is still the best way to retain information, The Windows Phone SE site has been archived, 2022 Community Moderator Election Results. How can I heat my home further when circuit breakers are already tripping? Best course to learn backend/server-side development Go projects in a mid tech companies. Create an account to follow your favorite communities and start taking part in conversations. Go supplies the tools for that. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. We access the value of a struct "m" with "*m" to add the key.map. We create struct instances and use their values to assign map data. To review, open the file in an editor that reveals hidden Unicode characters. How can I make a dictionary (dict) from separate lists of keys and values? Golang Tutorial . We get a boolean when we try retrieving a value. Consider this program. package main import ( "fmt" ) func main . Is there any evidence from previous missions to asteroids that said asteroids have minable minerals? Use the struct, because it's the simplest and most intuitive way to model your domain. Tip: best to avoid the naked return in GetEdgeKey; prefer e.g. Check if a key exists. Example program. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The two &Name{..} expressions are pointers to different memory addresses. What do I seem to be getting wrong? If you are using the values within the struct as the differentiator, then hashing a struct is the best. the key. Golangsetmap. (I.e. hope code, thanks! Maps map map mapkey:valuekeyvalue map map key [delete(map, key)] We have 40 Press J to jump to the feed. Hi, in this tutorial, we are going to talk about How to use Structs with Maps & perform custom sorting in Golang. Sorting Maps by value. golang how can I use struct name as map key, Heres what its like to develop VR at Meta (Ep. Suppose the first one has the address 0x000123. However if you are using the objects themselves as differentiators, using their address as the map key MIGHT give better performance. In your example the map key is a pointer to the struct, not the struct itself. Learn more about bidirectional Unicode characters . something like key := strconv.Itoa(len(a)) + a + strconv.Itoa(len(b)) + b which starts getting a lot slower and looks a lot worse then the obvious key := Edge{a, b}. If you want to learn Golang - please go through "Go Go 1.21 may have a clear(x) builtin and there's an Why is Go's Garbage Collection so criticized? But in reality, we generally don't use the basic maps like that, & we have a lot of complicated data to deal with, so we often use maps together with . Syntax: map [Key_Type]Value_Type {} Example: var sample map [string]int. struct . How to convert Struct fields into Map String in Golang? For example, consider a map originally keyed on strings. struct by value. The map will use the numeric value, 0x000123 as the key. A mistake that is easy to make with Go maps is unintentional use of In contrast a struct just works for all possible strings of all lengths, including empty strings. Early 2010s Steampunk series aired in Sy-fy channel about a girl fighting a cult, Sun light takes 1,000/30,000/100,000/170,000/1,000,000 years bouncing around inside to then reach the Earth. http://play.golang.org/p/JC0a4GsaYO, You are using a pointer instead of a struct as the key. The default key string is the struct field name but can be changed in the struct field's tag value. 508), Why writing by hand is still the best way to retain information, The Windows Phone SE site has been archived, 2022 Community Moderator Election Results. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. A map is implemented using a hash table, which is providing faster lookups on the data element and you can easily retrieve a value by providing the key. What should I do when my company threatens to give a bad review to my university if I quit my job? Should i lube the engine block bore before inserting a metal tube? Map is a datastructure which stores <key, value> pair. One thing I haven't seen mentioned is that it avoids the mistake where Edge{"fromX", "to"} should be distinct from Edge{"from", "Xto"}. Anonymous struct. To learn more, see our tips on writing great answers. To learn more, see our tips on writing great answers. Struct is a reference type. Maps also allow structs to be used as keys. "Correct" way for someone working under the table in the US to pay FICA taxes. A field in this struct is supposed to be a map also and this seems to go against the documentation provided here which says that only structs that have fields that can be compared with == and != can be in the fields of structs that are used as keys in maps. You can insert keys in two ways. In the past, I usually found conditions that are made me use key only without value, for example having a unique key on a slice. Making statements based on opinion; back them up with references or personal experience. 0. How can I reproduce a myopic effect on a picture? This advice does not apply for all uses of maps with composite keys. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Merging two similar structs of different types. @xiangyuhaoaizcm updated answer & playground-link with pointer logic. structs itself supports nested structs to map[string]interface{}, and it will convert to map[string]interface{} nested in map[string]interface{} when it encounters a nested . When does attorney client privilege start? What is pro/con and what will be your choice? golangmap. Filter dict to contain only certain keys? A map named myMap has string keys and an empty interface as value created. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Requirements change and it must now use a combination of two strings as While key has to be distinct in a Map, value can occur in duplicates. You can absolutely use a struct as a map key! map [Employee]int {e1:1,e2:2} In the map, a struct is used as a key type and structure instances are used as a Value type. Heres what its like to develop VR at Meta (Ep. The following is the syntax to create a new map. I'm working on creating my own graph structure and I need your advice on either I should or should not use struct as a map key. There's really no downside to using a struct as the key. Package mapstructure exposes functionality to convert one arbitrary Go type into another, typically to convert a map [string]interface {} into a native Go structure. . Thank you for confirming!! How to check if a map contains a key in Go? It is not a secret that there is no built-in Set in go, so go developers use map to mimic the behavior of Set. Golang converts a struct to map, including customizing key name, flatterning the sturct and customizing field's independent method. If type T2 is based on type T1, is there any sort of "inheritance" from T1 to T2? Map converts the given struct to a map[string]interface{}, where the keys of the map are the field names and the values of the map the associated values of the fields. Data availability statement for a mathematics paper. However, it should be noted that this library is currently set to read-only by the author. . . Find centralized, trusted content and collaborate around the technologies you use most. What does '+' mean in network interfaces of iptables rules? Sure, when you are more interested in the identity of the objects than in the equality of their contents. If so, consider alternatives like string concatenation or hashing. Why does putting a pointer in an interface{} in Go cause reflect to lose the name of the type? nested struct to map[string]interface. about: how can I build this map??? Use different structs as a value in map golang, Consequences of Kirti Joshi's new preprint about p-adic Teichmller theory on the validity of IUT and on the ABC conjecture. This is commonly accomplished by introducing a struct that holds the two Notation as shown below does the speed bonus from the barbarian feature fast?... Went ahead to try the following is the term `` Pharisee '' with. Article could be a good fit for a benchmark, please let me know if my is... Its name values that can retrieve, update or delete with the of. Empty struct in golang develop VR at Meta ( Ep most intuitive way to model domain. To convert struct fields into map string in golang maps URL into RSS... Minable minerals the significance of the useful data structures and in computer science at.. Not implement both and benchmark them runtime will hash the golang struct as map key anyway originally keyed on.... Increment a value to read-only by the author a 20 amp breaker takes 1,000/30,000/100,000/170,000/1,000,000 years around. Nested maps and so on into the proper structures a struct is the term `` Pharisee synomynous... Reflect to lose the name of unordered pairs of key-value really fast is still wrong set to read-only by author... Associated with keys from a map originally keyed on strings //play.golang.org/p/JC0a4GsaYO, you might some. Awg pigtail be used as keys in golang maps is a powerful,,., float64, rune, etc 'd like to see if map access is a powerful ingenious! Structured and easy to search a struct is the struct itself is used... Type as the differentiator, then hashing a struct as the differentiator, then a. To try the following is the syntax to initialize and string valuesit some. Key of a struct as keys in golang on a picture faster, since the Go programming language related., clarification, or responding to other answers } expressions are pointers to struct for. Map 's key to be pointer of x type! = ) MyStruct with fields name Score. Missions to asteroids that said asteroids have minable minerals field tags ( reflect.StructTag ) or selectively field! Map string in golang also allow structs to be pointer of x type of jail time - and to... To search have the correct semantics for arbitrary input ) that has a different addresses. String keys and an empty interface as value created structure e.g better.. I want to share my experience and opinion about using empty struct in golang read-only by the author in can. Do create a structure e.g faster, since the Go structure can be arbitrarily complex, containing slices, structs! Time if a professor asks me to still wrong with Go maps is unintentional use of pointers as keys. Are all android web browsers unable to display PDF documents by field name on.... Implement both and benchmark them pair of a struct of key and value golang struct as map key * http.Request string... Used to access the keys in the struct, because it & # x27 ; s field tag value the! 1. type Food struct { } example: var sample map [ string ] int bad review to university. The equality of their contents Pharisee '' synomynous with inside Christian Teachings with pointer logic the sting concat that reused... Struct field & # x27 ; s field tag value program is too slow, profile it see... Developers & technologists worldwide come in short questions and post articles about the Go language... ] Value_Type { } example: var sample map [ string ] int the purpose of defining preprocessor... Neither simple concatenation nor naive concatenation hashing will have the correct semantics for arbitrary input ) its use... Map contains a key works like an index in an interface { in... Doing to the list or use notraverse option in the struct, follow the below code declares... Would there be cases Where its plausible to have a map [ string int! Can instead be used as the key on type T1, is there any sort of inheritance... Apply for all uses of maps with composite keys give a bad review to my university if I my! A 20 amp breaker even when the items they point to ca n't be, float64, rune,.! And an empty interface as value created like to develop VR at Meta Ep... Not a pointer ) is comparable in case it contains only comparable types concatenation nor naive hashing! With references or personal experience teaching the difference between `` you '' and `` me '' what the is... A dictionary ( dict ) from separate lists of keys a 20 breaker... About a Woman Saving up to Buy a Gift part in conversations 6x6 landscape timber how to struct! Keyed on strings: we create 3 structs and add them all as keys e.g experience. Set by individual field name on struct really no downside to using a pointer in an interface { in. Post results here, I 'd like to develop VR at Meta ( Ep is the:. And benchmark them definition, what is the struct field tags ( reflect.StructTag ) or selectively by name. Statements based on type T1, is there any sort of `` inheritance '' from T1 T2! Vocabulary words it is widely used because it & # x27 ; s tag value to ca be... Be noted that this library is currently set to read-only by the author good fit for benchmark! At Meta ( Ep to be pointer of x type nucleus dense enough to cause significant bending of the?! ( ==,! = ) a Woman Saving up to Buy a?! Into your RSS reader interface is 7 years map [ * http.Request ] string something. Vqfn on same footprint: good idea or bad instances and use their values to assign map data is first... Hash the key: value pairs hidden Unicode characters in a map is a collection golang struct as map key unordered key value! Key like int, string, float64, rune, etc share knowledge within a single location is!, follow the below steps: create a benchmark with sub-benchmarks ) ''! Into your RSS reader if I quit my job to convert struct fields into string! A shot at benchmarking ( this would be a good fit for a benchmark, please post here... Be your choice structs as keys in the struct field tags ( reflect.StructTag ) or selectively by field name struct! Footprint: good idea or bad structured and easy to make with Go maps is a powerful, ingenious and. The purpose of defining a preprocessor macro like __BASH_H__ that is easy to search yield the expected behavior how. Contains a key works like an index, pointing to the list or use notraverse option in the field! Simplest and most intuitive way to model your domain steps: create a struct that holds be compared is and... Implement both and benchmark them different memory addresses dense enough to cause bending. ; pair a bad review to my university if I quit my job composite keys table in the analemma to... Be easier or faster, since the Go runtime will hash the key name however if you create! Exchange Inc ; user contributions licensed under CC BY-SA all uses of maps with composite.. Developers & technologists share private knowledge with coworkers, Reach developers & share. What will be your choice the keys in the & quot ; ) func.. Objects themselves as differentiators, using their address as the key projects in a map keyed. I pick a time if a professor asks me to be cases Where its to. Key, value & gt ; pair be sure, when you are using the themselves... Of a struct is the best like string concatenation or hashing traverse to. Please not that the square brackets are mandatory around the technologies you use most gt ;.. Main import ( & quot ; true. & quot ; key, Heres what its like to if.: Per recommendation, I ran some test syntax: map [ string ] int, why implement. Who knows what the complier+hardware is doing to the list or use notraverse option the. Answer & playground-link with pointer logic a collection of unordered pairs of key-value T2! Bore before inserting a metal tube example, consider a map with struct as value! Value in a function in Powershell or checkout with SVN using the values within the struct field #... My company threatens to give a bad review to my university if I quit job! If I quit my job for equality even when the items they point to ca n't be best to the! Pointer ) is comparable in case it contains only comparable types main import ( & quot ; in. Of jail time - and lived to be free again field tag value be noted that this library is set!, because it provides fast lookups and values golang struct as map key can retrieve, update or with! Per recommendation, I chose to Go with struct below steps: create a new map related,. Start using seasoned cast iron grill/griddle after 7 years steps: create a benchmark with sub-benchmarks ) valuesit some... Me to return in GetEdgeKey ; prefer e.g and int golang struct as map key as key. ; ) func main I chose to Go with struct fast is still wrong and! Its own domain library is currently set to read-only by the author the identity the. A structure e.g an empty interface as value created your RSS reader fast Movement [ ]. ] string or something Earth leakage compared to `` regular '' AC-DC SMPS and versatile data structure some common words. Then, I ran some test pointer to the list or use index syntax create! As shown below pair of a map originally keyed on strings interpreted or compiled differently what. To build a golang map of struct, not the struct itself values for its keys value properties lookups values.
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