golang with compile error: undefined: strings in strings.trim - go

I try to use golang deal with this problem 557. Reverse Words in a String III
my code as below:
import "fmt"
import ss "strings"
func reverseWords(s string) string {
words := ss.Split(s," ");
res := "";
for i:=0; i < len(words);i++{
curWord := ss.Split(words[i],"");
for j:=len(curWord)-1; j >= 0;j--{
res += curWord[j];
}
if(i!=len(words)-1){
res += " ";
}
}
return res;
}
func main(){
s := "Let's take LeetCode contest";
fmt.Println(reverseWords(s));
}
Everything is ok in my pc, it can pass compile at least.
However, when I submit in leetcode it tell me :
Line 67: undefined: strings in strings.Trim
I google this error but get nothing relevant info. As a beginner in golang, I need help. Everything will be appreciated.

You're importing strings under an alias:
import ss "strings"
That means that everywhere in that file, instead of referring to strings you must refer to ss, for example:
words := ss.Split(s," ")
If you use the default import:
import "strings"
Then you can refer to it as strings as normal.
Note that the currently accepted answer is wrong about two things: you can absolutely use the alias as you have it, you just have to refer to the package with the aliased name. It will not cause any issues if you use the name you gave it. Second, you absolutely do need to import the strings package - with or without an alias, your choice - if you want to refer to it.
On a completely unrelated side note, you should strongly consider running go fmt on your code, as it does not follow Go coding standards; for example, standard Go code omits the vast majority of semicolons. The code will work regardless, but you'll have an easier time getting help from other Go developers if your code is formatted the way everyone else is used to seeing it.

If you import strings package with different name then it will cause issue as it is used by the wrapper code to run the function completely.
No need to import strings package again. It will be added.
Just use it directly.
func reverseWords(s string) string {
words := strings.Split(s," ");
res := "";
for i:=0; i < len(words);i++{
curWord := strings.Split(words[i],"");
for j:=len(curWord)-1; j >= 0;j--{
res += curWord[j];
}
if(i!=len(words)-1){
res += " ";
}
}
return res;
}

Related

How can I scan a rune?

So far, I haven't been able to print a rune by scanning it with fmt.Scan and printing it with fmt.Print. This is the vary basic code I'm working on:
package main
import "fmt"
func main() {
var c rune
fmt.Scan(&c)
fmt.Printf("%c", c)
}
But it doesn't work, in fact, Printf doesn't produce any output. Instead, by manually assigning a char to my variable c (like var c rune = 'a', without using fmt.Scan), I'm able to print the wanted rune. How can I scan a rune?
As we know Scan return n and err so please check for error under Scan statement as follows
n, err := fmt.Scan(&c)
if err != nil {
fmt.Println(err)
}
It will clearly show you the error and why it was ignored.
Other than the above, please try it locally on your own laptop instead of the playground because on the playground it most of the time gives an EOF error as most of them do not support reading from the terminal.
I hope the above helps you in debugging the issue.
Other Reference:
Scanf ignores if not provided \n

In Go 1.18 strings.Title() is deprecated. What to use now? And how?

As suggested here names of people should be capitalized like John William Smith.
I'm writing a small software in Golang which gets last and first name from user's form inputs.
Until Go 1.18 I was using:
lastname = strings.Title(strings.ToLower(strings.TrimSpace(lastname)))
firstname = strings.Title(strings.ToLower(strings.TrimSpace(firstname)))
It works but now Go 1.18 has deprecated strings.Title().
They suggest to use golang.org/x/text/cases instead.
So I think I should change my code in something like this:
caser := cases.Title(language.Und)
lastname = caser.Title(strings.ToLower(strings.TrimSpace(lastname)))
firstname = caser.Title(strings.ToLower(strings.TrimSpace(firstname)))
It works the same as before.
The difference is for Dutch word like ijsland that should be titled as IJsland and not Ijsland.
The question
In the line caser := cases.Title(language.Und) I'm using Und because I don't know what language Tag to use.
Should I use language.English or language.AmericanEnglish or other?
So far it was like strings.Title() was using Und or English?
As mentioned in documentation strings.Title is deprecated and you should use cases.Title instead.
Deprecated: The rule Title uses for word boundaries does not handle
Unicode punctuation properly. Use golang.org/x/text/cases instead.
Here is an example code of how to use it as from two perspectives:
// Straightforward approach
caser := cases.Title(language.BrazilianPortuguese)
titleStr := caser.String(str)
// Transformer interface aware approach
src := []byte(s)
dest := []byte(s) // dest can also be `dest := src`
caser := cases.Title(language.BrazilianPortuguese)
_, _, err := caser.Transform(dest, src, true)
Make sure to take a look on the transform.Transformer.Transform and cases.Caser in order to understand what each parameter and return values mean, as well as the tool's limitations. For example:
A Caser may be stateful and should therefore not be shared between
goroutines.
Regarding what language to use, you should be aware of their difference in the results, besides that, you should be fine with any choice. Here is a copy from 煎鱼's summary on the differences that cleared it for me:
Go Playground: https://go.dev/play/p/xp59r1BkC9L
func main() {
src := []string{
"hello world!",
"i with dot",
"'n ijsberg",
"here comes O'Brian",
}
for _, c := range []cases.Caser{
cases.Lower(language.Und),
cases.Upper(language.Turkish),
cases.Title(language.Dutch),
cases.Title(language.Und, cases.NoLower),
} {
fmt.Println()
for _, s := range src {
fmt.Println(c.String(s))
}
}
}
With the following output
hello world!
i with dot
'n ijsberg
here comes o'brian
HELLO WORLD!
İ WİTH DOT
'N İJSBERG
HERE COMES O'BRİAN
Hello World!
I With Dot
'n IJsberg
Here Comes O'brian
Hello World!
I With Dot
'N Ijsberg
Here Comes O'Brian
So far it was like strings.Title() was using Und or English?
strings.Title() works based on ASCII, where cases.Title() works based on Unicode, there is no way to get the exact same behavior.
Should I use language.English or language.AmericanEnglish or other?
language.English, language.AmericanEnglish and language.Und all seem to have the same Title rules. Using any of them should get you the closest to the original strings.Title() behavior as you are going to get.
The whole point of using this package with Unicode support is that it is objectively more correct. So pick a tag appropriate for your users.
strings.Title(str) was deprecated, should change to cases.Title(language.Und, cases.NoLower).String(str)
package main
import (
"fmt"
"strings"
"golang.org/x/text/cases"
"golang.org/x/text/language"
)
func main() {
fmt.Println(strings.Title("abcABC")) // AbcABC
fmt.Println(cases.Title(language.Und, cases.NoLower).String("abcABC")) // AbcABC
}
Playground : https://go.dev/play/p/i0Eqh3QfxTx
Here is a straightforward example of how to capitalize the initial letter of each string value in the variable using the golang.org/x/text package.
package main
import (
"fmt"
"golang.org/x/text/cases"
"golang.org/x/text/language"
)
func main() {
sampleStr := "with value lower, all the letters are lowercase. this is good for poetry perhaps"
caser := cases.Title(language.English)
fmt.Println(caser.String(sampleStr))
}
Output : With Value Lower, All The Letters Are Lowercase. This Is Good For Poetry Perhaps
Playground Example: https://go.dev/play/p/_J8nGVuhYC9

Calling a function with Go Reflect

I was wondering if it was possible to not know a function name but call it anyway and get values from it. This lead me to the reflection package and I got pretty close but I’m not sure about the last step - if there is one. Again please forgive me if I am missing something obvious, this is my first attempt at doing anything in Go other than getting it setup.
Of course being a compiled language there is no need to iterate through things to find function names, I know them all, but this is something I want to see if it is possible… I’m playing and learning.
Below is the code. What I would really like to do is in the main line extract the values set in ModuleBoot() <“1.0012”, 23> and SomethingBoot() <“1.0000”, 10> but so far all as I can get is structure information. Perhaps that’s just the way it is but perhaps there is a step or change that can make it go the next step.
Hopefully I copied all the relevant code over correctly so it compiles as is:
// Using: go version go1.9.7 linux/amd64
=======================================
FILE: main.go
=======================================
package main
import (
"fmt"
"reflect"
"playing/modules/core"
)
func main() {
miType := reflect.TypeOf(core.ModuleInfo{})
fmt.Println("")
for i := 0; i < miType.NumMethod(); i++ {
method := miType.Method(i)
fmt.Println(method.Name)
in := make([]reflect.Value, method.Type.NumIn())
in[0] = reflect.ValueOf(core.ModuleInfo{})
//fmt.Println("Params in:", method.Type.NumIn(), "Params out:", method.Type.NumOut())
mi := method.Func.Call(in)
fmt.Println("mi:", mi)
fmt.Println("")
}
}
=======================================
FILE: playing/modules/core/something.go
=======================================
package core
func (mi ModuleInfo) SomethingBoot() ModuleInfo {
mi.Version = "1.0000"
mi.Priority = 10
return mi
}
=======================================
FILE: playing/modules/core/modules.go
=======================================
package core
type ModuleInfo struct {
Version string
Priority int
}
func (mi ModuleInfo) ModuleBoot() ModuleInfo {
mi.Version = "1.0012"
mi.Priority = 23
return mi
}
The output I got from this was:
Started delve with config "Debug"
SomethingBoot
mi: [<core.ModuleInfo Value>]
ModuleBoot
mi: [<core.ModuleInfo Value>]
delve closed with code 0
To get the return value as a ModuleInfo, get the underlying value of the first return value and type assert that interface value to ModuleInfo:
// mi has type core.ModuleInfo
mi := method.Func.Call(in)[0].Interface().(core.ModuleInfo)
Run it on the Playground.
You can cut some of the reflect code by type asserting the method to a function with the correct signature and calling that function directly:
for i := 0; i < miType.NumMethod(); i++ {
method := miType.Method(i).Func.Interface().(func(core.ModuleInfo) core.ModuleInfo)
mi := method(core.ModuleInfo{})
fmt.Println("Version", mi.Version)
fmt.Println("Priority", mi.Priority)
fmt.Println("")
}
Run it on the Playground
Go natively supports functions as values; you don't need reflection to do this.
In particular, if you make your two functions top-level functions (not specifically tied to a struct):
package core
type ModuleInfo struct { ... }
func SomethingBoot() ModuleInfo
func ModuleBoot() ModuleInfo
Then you can write a function that takes a function as a parameter:
func PrintVersion(func booter() core.ModuleInfo) {
mi := booter()
fmt.Printf("version %s\n", mi.Version)
}
And you can just pass the pre-existing functions as parameters:
PrintVersion(core.SomethingBoot)
PrintVersion(core.ModuleBoot)
Notice that there aren't parentheses after the function name: you are passing the function itself as a parameter, not calling the function and passing its return value.

Exported functions from another package

I am following instructions in https://golang.org/doc/code.html#Workspaces link and I build my first Go program.
So, I tried to make library with this instruction = https://golang.org/doc/code.html#Library
and everything is perfect until building hello.go, its gives me this error.
/hello.go:10:13: undefined: stringutil.Reverse
I've already rebuild my reverse.go.
Thats my code:
package main
import (
"fmt"
"github.com/d35k/stringutil"
)
func main() {
fmt.Printf(stringutil.Reverse("!oG ,olleH"))
}
that's my reverse.go (same as docs)
package stringutil
func reverse(s string) string {
r := []rune(s)
for i, j := 0, len(r)-1; i < len(r)/2; i, j = i+1, j-1 {
r[i], r[j] = r[j], r[i]
}
return string(r)
}
and my gopath variable
export GOPATH=$HOME/GoLang
and my files ar in
GoLang/src/github.com/mygithubusername/
Golang Tour specify exported name as
A name is exported if it begins with a capital letter. And When
importing a package, you can refer only to its exported names. Any
"unexported" names are not accessible from outside the package.
Change the name of reverse func to Reverse to make it exportable to main package. Like below
package stringutil
func Reverse(s string) string {
r := []rune(s)
for i, j := 0, len(r)-1; i < len(r)/2; i, j = i+1, j-1 {
r[i], r[j] = r[j], r[i]
}
return string(r)
}
A different problem with the same symptoms I ran into was that I was having two functions with the same name in Package B. Since two functions wih the same name but different types are no problem, I didn't think about it too much, however, VSCode didn't show the methods when I tried to use them in Package A, despite them being capitalized.
According to the question asked here
this is not supported by Go and requires you to change the function name or use introspection/an interface.
Thought I'd share it since googling brought me to this question here multiple times and it might be something other Go learners might run into as well...

Evaluate formula in Go

Using Go (golang) I'd like to take a string with a formula and evaluate it with pre-defined values. Here's a way to do it with python's parser module:
x = 8
code = parser.expr("(x + 2) / 10").compile()
print eval(code)
# prints 1
Any idea how to do it with Go?
This package will probably work for your needs: https://github.com/Knetic/govaluate
expression, err := govaluate.NewEvaluableExpression("(x + 2) / 10");
parameters := make(map[string]interface{}, 8)
parameters["x"] = 8;
result, err := expression.Evaluate(parameters);
You will probably need to resort to a library that interprets math statements or have to write your own parser. Python being a dynamic language can parse and execute python code at runtime. Standard Go cannot do that.
If you want to write a parser on your own, the go package will be of help. Example (On play):
import (
"go/ast"
"go/parser"
"go/token"
)
func main() {
fs := token.NewFileSet()
tr, _ := parser.ParseExpr("(3-1) * 5")
ast.Print(fs, tr)
}
The resulting AST (Abstract Syntax Tree) can then be traversed and interpreted as you choose (handling '+' tokens as addition for the now stored values, for example).
I have made my own equation evaluator, using Djikstra's Shunting Yard Algorithm.
It supports all operators, nested parenthesis, functions and even user defined variables.
It is written in pure go
https://github.com/marcmak/calc
go-exprtk package will probably meet all kinds of your needs to evaluate any kind of mathematical expression dynamically.
package main
import (
"fmt"
"github.com/Pramod-Devireddy/go-exprtk"
)
func main() {
exprtkObj := exprtk.NewExprtk()
exprtkObj.SetExpression("(x + 2) / 10")
exprtkObj.AddDoubleVariable("x")
exprtkObj.CompileExpression()
exprtkObj.SetDoubleVariableValue("x", 8)
fmt.Println(exprtkObj.GetEvaluatedValue())
}
This package has many capabilities
There is no such module in Go. You have to build your own. You could use subpackages of the go package, but they might be overkill for your application.
For expression or program evaluation, you can build a lexer and parser using lex and yacc, and specify exactly the syntax and semantics of your mini-language. A calculator has always been a standard yacc example, and the go versions of lex and yacc are no different.
Here's a pointer to the calc example: https://github.com/golang-samples/yacc/tree/master/simple
With this code you can evaluate dynamically any formula and return true or false:
package main
import (
"go/token"
"go/types"
)
func main() {
fs := token.NewFileSet()
tv, err := types.Eval(fs, nil, token.NoPos, "(1 + 4) >= 5")
if err != nil {
panic(err)
}
println(tv.Value.String())
}
There's nothing built in that could do that (remember, Go is not a dynamic language).
However, you can always use bufio.Scanner and build your own parser.
Googling around I found this: https://github.com/sbinet/go-eval
It appears to be an eval loop for Go.
go get github.com/sbinet/go-eval/cmd/go-eval
go install github.com/sbinet/go-eval/cmd/go-eval
go-eval

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