hashstructure

README

hashstructure

hashstructure is a Go library for creating a unique hash value for arbitrary values in Go.

This can be used to key values in a hash (for use in a map, set, etc.) that are complex. The most common use case is comparing two values without sending data across the network, caching values locally (de-dup), and so on.

Features

• Hash any arbitrary Go value, including complex types.

• Tag a struct field to ignore it and not affect the hash value.

• Tag a slice type struct field to treat it as a set where ordering doesn't affect the hash code but the field itself is still taken into account to create the hash value.

• Optionally specify a custom hash function to optimize for speed, collision avoidance for your data set, etc.

Installation

Standard go get:

$ go get github.com/mitchellh/hashstructure

Usage & Example

For usage and examples see the Godoc.

A quick code example is shown below:

type ComplexStruct struct {
    Name     string
    Age      uint
    Metadata map[string]interface{}
}

v := ComplexStruct{
    Name: "mitchellh",
    Age:  64,
    Metadata: map[string]interface{}{
        "car":      true,
        "location": "California",
        "siblings": []string{"Bob", "John"},
    },
}

hash, err := hashstructure.Hash(v, nil)
if err != nil {
    panic(err)
}

fmt.Printf("%d", hash)
// Output:
// 2307517237273902113

Documentation

Index

• func Hash(v interface{}, opts *HashOptions) (uint64, error)
• type HashOptions
• type Includable
• type IncludableMap

Examples

• Hash

Functions

func Hash

func Hash(v interface{}, opts *HashOptions) (uint64, error)

Hash returns the hash value of an arbitrary value.

If opts is nil, then default options will be used. See HashOptions for the default values.

Notes on the value:

• Unexported fields on structs are ignored and do not affect the hash value.

• Adding an exported field to a struct with the zero value will change the hash value.

For structs, the hashing can be controlled using tags. For example:

struct {
    Name string
    UUID string `hash:"ignore"`
}

The available tag values are:

• "ignore" or "-" - The field will be ignored and not affect the hash code.

• "set" - The field will be treated as a set, where ordering doesn't affect the hash code. This only works for slices.

Example

type ComplexStruct struct {
	Name     string
	Age      uint
	Metadata map[string]interface{}
}

v := ComplexStruct{
	Name: "mitchellh",
	Age:  64,
	Metadata: map[string]interface{}{
		"car":      true,
		"location": "California",
		"siblings": []string{"Bob", "John"},
	},
}

hash, err := Hash(v, nil)
if err != nil {
	panic(err)
}

fmt.Printf("%d", hash)

Output:

6691276962590150517

Types

type HashOptions

type HashOptions struct {
	// Hasher is the hash function to use. If this isn't set, it will
	// default to FNV.
	Hasher hash.Hash64

	// TagName is the struct tag to look at when hashing the structure.
	// By default this is "hash".
	TagName string

	// ZeroNil is flag determining if nil pointer should be treated equal
	// to a zero value of pointed type. By default this is false.
	ZeroNil bool
}

HashOptions are options that are available for hashing.

type Includable

type Includable interface {
	HashInclude(field string, v interface{}) (bool, error)
}

Includable is an interface that can optionally be implemented by a struct. It will be called for each field in the struct to check whether it should be included in the hash.

type IncludableMap

type IncludableMap interface {
	HashIncludeMap(field string, k, v interface{}) (bool, error)
}

IncludableMap is an interface that can optionally be implemented by a struct. It will be called when a map-type field is found to ask the struct if the map item should be included in the hash.