Programming language: Go
License: GNU General Public License v3.0 or later
Tags: Utilities    

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A Common Architecture for String Utilities in Go.

UNIS shares a common architecture and the necessary interfaces that will help you to refactor your project or application to a better place to work on. Choose one way to organise your string utilities, across your different projects.

Developers can now, move forward and implement their own types of string utilities based on the UNIS architecture.

Apply good design patterns from the beginning and you will be saved from a lot of work later on. Trust me.


The only requirement is the Go Programming Language.

$ go get -u github.com/esemplastic/unis

What's inside?

  • Processor: Manipulates a receiver string, based on the implementation, and returns its new format.
  • Validator: Validates a receiver string, based on the implementation, and returns a boolean and an error.
  • Divider: Splits a receiver string into two pieces, based on the implementation, and returns them.
  • Joiner: Receives two strings, combines them into one, based on the implementation, and returns it.

Getting started

UNIS contains some basic implementations that you can see and learn from!

First of all, let's take look at the unis.Processor interface.

// Processor is the most important interface of this package.
// It's being used to implement basic string processors.
// Users can use all these processors to build more on their packages.
// A Processor should change the "original" and returns its result based on that.
type Processor interface {
    // Process accepts an "original" string and returns a result based on that.
    Process(original string) (result string)

As you can see, it contains just a function which accepts a string and returns a string. Everything implements that interface only -- No, please don't close the browser yet!

TIP: Convert standard strings or path functions to UNIS.Processor

The majority of strings and path packages contain functions like strings.ToLower which is a type of func(string) string, guess what -- unis.ProcessorFunc it's type of func(string)string too, so UNIS is 100% compatible with standard library!

Proof of concept:

// [...]
pathCleaner := unis.ProcessorFunc(path.Clean)
toLower := unis.ProcessorFunc(strings.ToLower)

unis.NewChain(pathCleaner, toLower)
// [...]

Let's begin

How many times are you using strings.Replace in your project? -- Correct, a lot. Spawning strings.Replace many times can be a dangerous decision because you may forget a replacement somewhere after a trivial change.

UNIS has a function which can help you structure all of your strings.Replace to one spot based on the replacements. Replacements is just a map[$oldstring]$newstring.

// NewReplacer accepts a map of old and new string values.
// The "old" will be replaced with the "new" one.
// Same as for loop with a strings.Replace("original", old, new, -1).
NewReplacer(replacements map[string]string) ProcessorFunc

ProcessorFunc is just an ease-to-use "alias" for a Processor. It's a func that accepts the same arguments as Processor.Process and in the same time implements the Processor interface. Exactly like the net/http.HandlerFunc function.


package main

import (

const slash = "/"

// SlashFixer removes double (system) slashes and returns the fixed path.
var SlashFixer = unis.NewReplacer(map[string]string{
    "\\": slash,
    "//": slash,

func main() {
    original := "\\home\\/users//Downloads"
    result := SlashFixer(original) // /home/users/Downloads
    print(" |> ")

SlashFixer is an unis.ProcessorFunc, can be called as SlashFixer.Process(string) or simply SlashFixer(string).


// Processors is a list of string Processor.
Processors []Processor

// NewChain returns a new chain of processors
// the result of the first goes to the second and so on.
NewChain(processors ...Processor) ProcessorFunc


package main

import (


func NewPathNormalizer() unis.Processor {
    slash := "/"
    replacer := unis.NewReplacer(map[string]string{
        `\`:  slash,
        `//`: slash,

    suffixRemover := unis.NewSuffixRemover(slash)
    slashPrepender := unis.NewTargetedJoiner(0, slash[0])

    toLower := unis.ProcessorFunc(strings.ToLower) // convert standard functions to UNIS and add to the chain.
    cleanPath := unis.ProcessorFunc(path.Clean)    // convert standard functions to UNIS and add to the chain.
    return unis.NewChain(

var defaultPathNormalizer = NewPathNormalizer()

func NormalizePath(path string) string {
    if path == "" {
        return path
    return defaultPathNormalizer.Process(path)

func main() {
    original := "api\\////users/"
    result := NormalizePath(original) // /api/users
    print(" |> ")


// NewConditional runs the 'p' processor, if the string didn't
// changed then it assumes that that processor has being a failure
// and it returns a Chain of the 'alternative' processor(s).
NewConditional(p Processor, alternative ...Processor) ProcessorFunc


// NewPrefixRemover accepts a "prefix" and returns a new processor
// which returns the result without that "prefix".
NewPrefixRemover(prefix string) ProcessorFunc

// NewPrepender accepts a "prefix" and returns a new processor
// which returns the result prepended with that "prefix".
NewPrepender(prefix string) ProcessorFunc

// NewExclusivePrepender accepts a "prefix" and returns a new processor
// which returns the result prepended with that "prefix"
// if the "original"'s prefix != prefix.
// The difference from NewPrepender is that
// this processor will make sure that
// the prefix is that "prefix" series of characters,
// i.e:
// 1. "//path" -> NewPrepender("/") |> "//path"
//    It has a prefix already, so it doesn't prepends the "/" to the "//path",
//    but it doesn't checks if that is the correct prefix.
// 1. "//path" -> NewExclusivePrepender("/") |> "/path"
//     Checks if that is the correct prefix, if so returns as it's,
//     otherwise replace the duplications and prepend the correct prefix.
NewExclusivePrepender(prefix string) ProcessorFunc


// NewSuffixRemover accepts a "suffix" and returns a new processor
// which returns the result without that "suffix".
NewSuffixRemover(suffix string) ProcessorFunc

// NewAppender accepts a "suffix" and returns a new processor
// which returns the result appended with that "suffix".
NewAppender(suffix string) ProcessorFunc 


// NewRange accepts "begin" and "end" indexes.
// Returns a new processor which tries to
// return the "original[begin:end]".
NewRange(begin, end int) ProcessorFunc

// NewRangeBegin almost same as NewRange but it
// accepts only a "begin" index, that means that
// it assumes that the "end" index is the last of the "original" string.
// Returns the "original[begin:]".
NewRangeBegin(begin int) ProcessorFunc

// NewRangeEnd almost same as NewRange but it
// accepts only an "end" index, that means that
// it assumes that the "start" index is 0 of the "original".
// Returns the "original[0:end]".
NewRangeEnd(end int) ProcessorFunc


// NewTargetedJoiner accepts an "expectedIndex" as int
// and a "joinerChar" as byte and returns a new processor
// which returns the result concated with that "joinerChar"
// if the "original" string[expectedIndex] != joinerChar.
// i.e:
// 1. "path", NewTargetedJoiner(0, '/') |> "/path"
// 2. "path/anything", NewTargetedJoiner(5, '*') |> "path/*anything".
NewTargetedJoiner(expectedIndex int, joinerChar byte) ProcessorFunc

Bonus: Divider

We saw that everything are Processors at the end. UNIS has some other interfaces like Divider too, which should split a string into two different string pieces, and Joiner which should joins two pieces into one.

// Divider should be implemented by all string dividers.
type Divider interface {
    // Divide takes a string "original" and splits it into two pieces.
    Divide(original string) (part1 string, part2 string)

// NewDivider returns a new divider which splits
// a string into two pieces, based on the "separator".
// On failure returns the original path as its first
// return value, and empty as it's second.
NewDivider(separator string) Divider

// NewInvertOnFailureDivider accepts a Divider "divider"
// and returns a new one.
// It calls the previous "divider" if succed then it returns
// the result as it is, otherwise it inverts the order of the result.
// Rembmer: the "divider" by its nature, returns the original string
// and empty as second parameter if the divide action has being a failure.
NewInvertOnFailureDivider(divider Divider) Divider

// Divide is an action which runs a new divider based on the "separator"
// and the "original" string.
Divide(original string, separator string) (string, string)


// Validator is just another interface
// for string utilities.
// All validators should implement this interface.
// Contains only one function "Valid" which accepts
// a string and returns a boolean and an error.
// It should compare that string "str" with
// something and returns a true, nil or false, err.
// Validators can be used side by side with Processors.
// See .If for more.
type Validator interface {
    Valid(str string) (ok bool, err error)

// ValidatorFunc is just an "alias" for the Validator interface.
// It implements the Validator.
type ValidatorFunc func(str string) (bool, error)

Validators can be used side by side with Processors.

// If receives a "validator" Validator and two Processors,
// the first processor will be called when that validator passed,
// the second processor will be called when the validator failed.
// Both of the processors ("succeed" and "failure"), as always,
// can be results of .NewChain.
// Returns a new string processor which checks the "validator"
// against the "original" string, if passed then it runs the
// "succeed", otherwise it runs the "failure".
// Remember: it returns a ProcessorFunc, meaning that can be used in a new chain too.
If(validator Validator, succeed Processor, failure Processor) ProcessorFunc


// [...]
mailTo := unis.If(unis.IsMail, unis.NewPrepender("mailto:"), unis.ClearProcessor)
// it checks if a string is an e-mail,if so then it runs the prepender
// otherwise it runs the unis.ClearProcessor which returns an empty string.

mailTo("[email protected]") // returns "mailto:[email protected]"
mailTo("[email protected]") // returns ""

// [...]

IsMail is a ValidatorFunc, see expression_validator_test.go for more.

IsMail is a built'n Validator based on a the expression matcher which accepts a regex expression and validates the receiver string.

// NewMatcher returns a new validator which
// returns true and a nil error if the "expression"
// matches against a receiver string.
NewMatcher(expression string) ValidatorFunc

Let's create a custom matcher which matches if a string is a positive number.

package main

import (

func main() {
    isPositiveNumber := unis.NewMatcher("^([0-9]*[1-9][0-9]*(\.[0-9]+)?|[0]+\.[0-9]*[1-9][0-9]*)$")
    isPositiveNumber("-0") // or isPositiveNumber.Valid("-0"), returns false, nil 
    isPositiveNumber("0") // returns false, nil
    isPositiveNumber("0.1") // returns true, nil
    isPositiveNumber("-1") // returns false, nil
    isPositiveNumber("1") // returns true, nil
    isPositiveNumber("astring") // returns false, nil

The error output argument of the NewMatcher is filled when the expression is invalid.

m := NewMatcher("\xf8\xa1\xa1\xa1\xa1")
ok, err := m.Valid("something") // ok is false, err.Error() is "error parsing regexp: invalid UTF-8: ...."

UNIS never panics on its own functions, but we need a way to notify the user, in case he doesn't catch the error second output argument, that something critical happened before the validator returns (the regexp.Compile is happening before returning the validator).

So we have a global Logger variable which accepts a receiver string message and logs to the console by-default. This behavior can be changed by setting the Logger to an empty func.

unis.Logger = func(string){} // disables the logging of the "panic-level" messages.


Help me share realistic design patterns by starring the project! If you would like to add your implementation of a UNIS Processor, feel free to push a PR!


The UNIS philosophy is to provide small, robust tooling for common string actions, making it a great solution for an extensible project.

I would love to see UNIS as a common place of all Go's extensible string utilities that any Gopher will find and use with ease. The goal is to make this repository authored by a Community which cares about code extensibility, stability and buety!


Current: 0.0.3
Date: 8 May 2017

Read more about Semantic Versioning 2.0.0


I'd love to see contributions!

If you are interested in contributing to the UNIS project, please read the [SPECS.md](SPECS.md) and make a PR.


A list of all contributors can be found [here](CONTRIBUTORS.md).


  • [x] Tests
  • [x] Documentation
  • [ ] Advanced Examples and Usage on a real project.


Unless otherwise noted, the source files are distributed under the 3-Clause BSD License found in the [LICENSE](LICENSE) file.

*Note that all licence references and agreements mentioned in the UNIS README section above are relevant to that project's source code only.