jq

func Get ¶

func Get(obj any, jspath string) (val any, err error)

Get returns the value at jspath in obj.

An empty path returns obj itself unless obj is nil. Values containing maps, slices, or pointers may share their backing data with obj.

When traversal reaches an array or slice, a component is a valid index only if it is "0" or begins with an ASCII digit from '1' through '9' followed by zero or more ASCII decimal digits. The index must be at most 4294967294 and representable as int; otherwise the error matches ErrPathNotFound.

func GetAs ¶

func GetAs[T any](obj any, jspath string) (val T, err error)

GetAs returns the value at jspath in obj as T.

It returns ErrTypeMismatch when the resolved value is not assignable to T.

func Set ¶

func Set(obj any, jspath string, val any) (changed bool, err error)

Set updates jspath in obj and reports whether it performed a write.

obj must be a non-nil pointer. An empty path replaces the pointed-to value. Array and slice components follow the index syntax documented by Get. A path into a settable slice may append one element by using an index equal to the slice's current length. Map paths address existing string-keyed entries and do not create new entries. A nil val stores the destination type's zero value.

Set leaves obj unchanged when it returns an error. It does not synchronize access to obj; callers must prevent concurrent reads and writes.

func SetChecked ¶ added in v0.2.0

func SetChecked(obj any, jspath string, val any, check func() error) (changed bool, err error)

SetChecked updates jspath only when check accepts the resulting object.

SetChecked first applies the same operation as Set. If Set reports a write, SetChecked calls check exactly once while obj contains the tentative result. A nil error commits the change. If check returns an error, SetChecked restores obj, returns false, and returns that error unchanged. If check panics, SetChecked restores obj before the panic continues. A nil check behaves like Set.

check is not called for an invalid operation or when Set reports no write. It may inspect obj, including by calling Get, but must not mutate obj or values reachable from it, call Set or SetChecked on them, or retain references into a rejected tentative value. Rollback covers only mutations made by SetChecked itself.

SetChecked does not synchronize access to obj. Callers must prevent concurrent access for the entire call, including while check runs.

package main

import (
	"encoding/json"
	"errors"
	"fmt"

	"github.com/linkdata/jq"
)

func main() {
	value := []string{"one"}
	maxBytes := len(`["one"]`)

	_, err := jq.SetChecked(&value, "1", "two", func() (err error) {
		var data []byte
		if data, err = json.Marshal(value); err == nil && len(data) > maxBytes {
			err = errors.New("value is too large")
		}
		return
	})

	fmt.Println(value)
	fmt.Println(err)
}

Output:
[one]
value is too large