Accessing fields in nested structs

How do I reference a field in the "AllData" struct below from the main "Forecast" struct? e.g if I wanted to reference "TemperatureMax from Forecast -> Daily?

type AllData struct {
	Time                       float64 `json:"time"`
	Summary                    string  `json:"summary"`
	Icon                       string  `json:"icon"`
	TemperatureMin             float64 `json:"temperatureMin"`
	TemperatureMinTime         float64 `json:"temperatureMinTime"`
	TemperatureMax             float64 `json:"temperatureMax"`
}

type HourlyData struct {
	Summary string        `json:"summary"`
	Icon    string        `json:"icon"`
	Data    []CurrentData `json:"data"`
}

type DailyData struct {
	Summary string    `json:"summary"`
	Icon    string    `json:"icon"`
	Data    []AllData `json:"data"`
}

type Forecast struct {
	Latitude  float64     `json:"latitude"`
	Longitude float64     `json:"longitude"`
	Timezone  string      `json:"timezone"`
	Offset    int         `json:"offset"`
	Currently CurrentData `json:"currently"`
	Hourly    HourlyData  `json:"hourly"`
	Daily     DailyData   `json:"daily"`
	Flags     Flags       `json:"flags"`
}

You can access an AllData field from a Forecast struct by providing an index into the Data slice in DailyData. Consider this stripped-down example of your question:

package main

import "fmt"

type AllData struct {
	Summary string
}

type DailyData struct {
	Data []AllData
}

type Forecast struct {
	Daily DailyData
}

func main() {
	a := AllData{"summary"}
	s := []AllData{a}
	d := DailyData{s}
	f := Forecast{d}

	val := f.Daily.Data[0].Summary

	fmt.Println(val)
}

In main, we read the Summary field from the AllData struct at index 0 of the DailyData's Data slice. This prints summary to the console.

Optionally, we could access multiple AllData structs by ranging over the slice in DailyData:

func main() {
	a1 := AllData{"summary1"}
	a2 := AllData{"summary2"}
	a3 := AllData{"hello"}
	s := []AllData{a1, a2, a3}
	d := DailyData{s}
	f := Forecast{d}

	for _, val := range f.Daily.Data {
		fmt.Println(val.Summary)
	}
}

The above prints:

summary1
summary2
hello