Enjoy a slice! pie is a code generator for dealing with slices that focuses on type safety, performance and immutability.

• Quick Start
  • Built-in Types
  • Custom Types And Structs
  • Limiting Functions Generated
• Functions
• FAQ
  • What are the requirements?
  • What are the goals of pie?
  • Can I contribute?
  • Why is the emoji a slice of pizza instead of a pie?

Install/update:

go get -u github.com/elliotchance/pie

pie ships with some slice types ready to go (pun intended). These include:

• typeStrings[]string
• typeFloat64s[]float64
• typeInts[]int

These can be used without needing go generate. For example:

package main

import (
    "github.com/elliotchance/pie/pie"
    "fmt"
)

func main() {
    name := pie.Strings{"Bob", "Sally", "John", "Jane"}.
        Unselect(func (name string) {
            return strings.HasPrefix(name, "J")
        }).
        Transform(strings.ToUpper).
        Last()

    fmt.Println(name) // "SALLY"
}

Annotate the slice type in your source code:

type Car struct {
    Name, Color string
}

//go:generate pie Cars
type Cars []Car

Run go generate. This will create a file called cars_pie.go. You should commit this with the rest of your code. Run go generate any time you need to add more types.

Now you can use the slices:

cars := Cars{
    {"Bob", "blue"},
    {"Sally", "green"},
    {"John", "red"},
    {"Jane", "red"},
}

redCars := cars.Select(func(car Car) bool {
    return car.Color == "red"
})

// redCars = Cars{{"John", "red"}, {"Jane", "red"}}

Or, more complex operations can be chained:

cars.Unselect(func (car Car) {
        return strings.HasPrefix(car.Name, "J")
    }).
    Transform(func (car Car) Car {
        car.Name = strings.ToUpper(car.Name)
        
        return car
    }).
    Last()

// Car{"SALLY", "green"}

By default all functions will be generated. This is easy to get going but creates a lot of unused code. You can limit the functions generated by chaining the function names with a dot syntax, like:

//go:generate myInts.Average.Sum myStrings.Select

This will only generate myInts.Average, myInts.Sum and myStrings.Select.

pie supports many Go versions, all the way back to Go 1.8.

1. Type safety. I never want to hit runtime bugs because I could pass in the wrong type, or perform an invalid type case out the other end.

2. Performance. The functions need to be as fast as native Go implementations otherwise there's no point in this library existing.

3. Nil-safe. All of the functions will happily accept nil and treat them as empty slices. Apart from less possible panics, it makes it easier to chain.

4. Immutable. Functions never modify inputs, unlike some built-ins such as sort.Strings.

Pull requests are always welcome.

Here is a comprehensive list of steps to follow to add a new function:

1. Create a new file in the functions/ directory. The file should be named the same as the function. You must include documentation for your function.

2. Update functions/main.go to register the new function by adding an entry to Functions. Make sure you choose the correct For value that is appropriate for your function.

3. Run go generate ./... && go install && go generate ./.... The first generate is to create the pie templates, install will update your binary for the annotations and the second generate will use the newly created templates to update the generated code for the internal types. If you encounter errors with your code you can safely rerun the command above.

4. If you chose ForAll or ForStructs, then you must add unit tests to pie/carpointers_test.go and pie/cars_test.go.

5. If you chose ForAll, ForNumbersAndStrings or ForNumbers, then you must add unit tests to pie/float64s_test.go and pie/ints_test.go.

6. If you chose ForAll or ForStrings, then you must add unit tests to pie/strings_test.go.

7. Update the README to list the new functions.

I wanted to pick a name for the project that was short and had an associated emoji. I liked pie, but then I found out that the pie emoji is not fully supported everywhere. I didn't want to change the name of the project to cake, but pizza pie still made sense. I'm not sure if I will change it back to a pie later.