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Cannot Assign To Golang


rsc commented Dec 4, 2013 Comment 8: Labels changed: added release-none, removed go1.3maybe. For now this is a use once and exit the program. package main type data struct { name string } func main() { m := map[string]*data {"x":{"one"}} m["z"].name = "what?" //??? } "nil" Interfaces and "nil" Interfaces Values level: advanced This is package main import ( "fmt" "time" ) func main() { ch := make(chan int) done := make(chan struct{}) for i := 0; i < 3; i++ { go func(idx int) { have a peek at this web-site

Fails: package main import "fmt" func main() { x := "text" x[0] = 'T' fmt.Println(x) } Compile Error: /tmp/sandbox305565531/main.go:7: cannot assign to x[0] Works: package main import "fmt" func main() { rsc commented Dec 4, 2013 Comment 9: Labels changed: added repo-main. This also means that it's ok to return references to local variables, which is not ok in other languages like C or C++. Fails: package main import "fmt" func doRecover() { fmt.Println("recovered =>",recover()) //prints: recovered => } func main() { defer func() { doRecover() //panic is not recovered }() panic("not good") } Updating https://github.com/golang/go/issues/3117

Golang Cannot Assign To Function

Please discuss that on the golang-nuts mailing list (but please note that we are not going to remove pointers from Go) rsc added this to the Unplanned milestone Apr 10, 2015 If your byte slices contain secrets (e.g., cryptographic hashes, tokens, etc.) that need to be validated against user-provided data, don't use reflect.DeepEqual(), bytes.Equal(), or bytes.Compare() because those functions will make your Finally, you initialize each inner slice by reslicing the raw data slice. Sending data to a closed channel causes a panic.

You'll need to create a custom http transport configuration for it. permalinkembedsavegive gold[–]clbanning 0 points1 point2 points 7 months ago(0 children)or: https://play.golang.org/p/FhCF75eUtW permalinkembedsavegive gold[–]RalphCorderoy 0 points1 point2 points 7 months ago(0 children)A reference to the relevant part of https://golang.org/ref/spec that states this restriction would be handy. package main import ( "fmt" "bytes" ) func main() { path := []byte("AAAA/BBBBBBBBB") sepIndex := bytes.IndexByte(path,'/') dir1 := path[:sepIndex] dir2 := path[sepIndex+1:] fmt.Println("dir1 =>",string(dir1)) //prints: dir1 => AAAA fmt.Println("dir2 =>",string(dir2)) //prints: Golang Map Struct Key package main import "fmt" func main() { x := []int{1,2,3} func(arr []int) { arr[0] = 7 fmt.Println(arr) //prints [7 2 3] }(x) fmt.Println(x) //prints [7 2 3] } Unexpected Values in

If you make this mistake in a new code block there will be no compiler error, but your app will not do what you expect. Terms Privacy Security Status Help You can't perform that action at this time. The for range clauses with string variables will try to interpret the data as UTF8 text. Variables referenced through interfaces are also not addressable.

By default, vet will not perform any shadowed variable checks. Golang Struct To Map String Interface Hot Network Questions One Very Odd Email How do I sort files into a sub-folder based on filename part? Is the English word "ikebana" a suitable translation for "華道"? m := map[int][1]int{1: [1]int{1}} m[1][0]++ // This doesn't work When you expand this last line, you get: arr := m[1] arr[0] = arr[0] + 1 Because arr is actually a copy

Golang Cannot Assign To Slice

package main import ( "fmt" "os" "path/filepath" ) func main() { if len(os.Args) != 2 { os.Exit(-1) } start, err := os.Stat(os.Args[1]) if err != nil || !start.IsDir(){ os.Exit(-1) } var Is it safe to use cheap USB data cables? Golang Cannot Assign To Function Singular cohomology and birational equivalence Can I switch from past tense to present tense in an epilogue? Golang Cannot Assign To String Another option is to use one defer call to close response bodies for all failed and successful requests.

Reload to refresh your session. http://electrictricycle.net/cannot-assign/cannot-assign-a-nil-to-a.html If you really need the imported package you can use the blank identifier, _, as its package name to avoid this compilation failure. This is an unfortunate violation of Go's general memory safeness. Iteration Values For Strings in "range" Clauses level: beginner The index value (the first value returned by the "range" operation) is the index of the first byte for the current "character" Golang Map Struct Value

The inner slices are independent of each other. And then if m["x"] has not be createdhow would we do that.You take the value out of the map, modify it and put it back.eg, http://play.golang.org/p/OawL6QIXuOThe other option is to store Fails: package main func main() { var x string = nil //error if x == nil { //error x = "default" } } Compile Errors: /tmp/sandbox630560459/main.go:4: cannot use nil as type http://electrictricycle.net/cannot-assign/cannot-assign.html package main import ( "fmt" "os" "path/filepath" ) func main() { if len(os.Args) != 2 { os.Exit(-1) } start, err := os.Stat(os.Args[1]) if err != nil || !start.IsDir(){ os.Exit(-1) } var

That is awesome. Golang Map Empty Struct That's it, no other info. Not every variable is addressable though.

If you don't specify the variable type the compiler will fail to compile your code because it can't guess the type.

package main import "fmt" func get() []byte { raw := make([]byte,10000) fmt.Println(len(raw),cap(raw),&raw[0]) //prints: 10000 10000 res := make([]byte,3) copy(res,raw[:3]) return res } func main() { data := get() fmt.Println(len(data),cap(data),&data[0]) //prints: You reslice the path to reference each directory modifying the first folder name and then you combine the names to create a new path. Map elements are not addressable. Golang Assignment To Entry In Nil Map This behavior is different from the behavior you get using the bytes.Equal() function.

For numerical computation apps that rely on dynamic multi-dimensional arrays it's far from ideal in terms of performance and complexity. go share|improve this question edited Sep 24 '15 at 0:41 Jonathan Leffler 443k62516827 asked Sep 24 '15 at 0:29 sbeam 1,55221533 marked as duplicate by Dave C, nemogo Users with the Unmarshalling JSON Numbers into Interface Values level: intermediate By default, Go treats numeric values in JSON as float64 numbers when you decode/unmarshal JSON data into an interface. have a peek here Indexing into maps with integer values has some reference semantic to it - the integer can be mutated in place.

You could use a pointer to the array instead. Same for m[0]++ m[0].M() already works for value receivers and pointer values. Works: package main import ( "fmt" "time" ) func main() { data := []string{"one","two","three"} for _,v := range data { vcopy := v // go func() { fmt.Println(vcopy) }() } time.Sleep(3 Even though your function gets a copy of the slice variable it still references the original data.

package main import ( "fmt" "reflect" "encoding/json" ) func main() { var str string = "one" var in interface{} = "one" fmt.Println("str == in:",str == in,reflect.DeepEqual(str, in)) //prints: str == in: Fails: package main func main() { var x = nil //error _ = x } Compile Error: /tmp/sandbox188239583/main.go:4: use of untyped nil Works: package main func main() { var x interface{} package main func main() { x := 2 y := 4 table := make([][]int,x) for i:= range table { table[i] = make([]int,y) } } Creating a dynamic multi-dimensional array using slices Others are due to faulty assumptions and missing details.

It's an easy mistake to make for new Go developers confusing the deferred code execution rules with the variable scoping rules. First Skills to Learn for Mountaineering Is it acceptable to ask an unknown professor for help in a related field during his office hours? That doesn't work for m[0].f Instead we have to fetch a pointer, as you suggest, and assign through the pointer. Fails: package main import "fmt" func main() { fmt.Println(~2) //error } Compile Error: /tmp/sandbox965529189/main.go:6: the bitwise complement operator is ^ Works: package main import "fmt" func main() { var d uint8