Unmarshaling unnamed JSON array of unnamed objects

The JSON I am trying to unmarshal with Go is unnamed array of unnamed objects:

[
{
    "date": 1394062029,
    "price": 654.964,
    "amount": 5.61567,
    "tid": 31862774,
    "price_currency": "USD",
    "item": "BTC",
    "trade_type": "ask"
},
{
    "date": 1394062029,
    "price": 654.964,
    "amount": 0.3,
    "tid": 31862773,
    "price_currency": "USD",
    "item": "BTC",
    "trade_type": "ask"
},
{
    "date": 1394062028,
    "price": 654.964,
    "amount": 0.0193335,
    "tid": 31862772,
    "price_currency": "USD",
    "item": "BTC",
    "trade_type": "bid"
}
]

I can successfully unmarshal the object and print the complete tradesResult array as %#v, but when I try to access element of the array I get the following error.

prog.go:41: invalid operation: tradeResult[0] (index of type *TradesResult)

Here is example code you can run to try the problem:

// You can edit this code!
// Click here and start typing.
package main

import (
	"fmt"
	"io/ioutil"
	"net/http"
	"encoding/json"
)

type TradesResultData struct {
	Date     float64 `json:"date"`
	Price    float64 `json:"price"`
	Amount   float64 `json:"amount"`
	Trade    float64 `json:"tid"`
	Currency string  `json:"price_currency"`
	Item     string  `json:"item"`
	Type     string  `json:"trade_type"`
}

type TradesResult []TradesResultData

func main() {
	resp, err := http.Get("https://btc-e.com/api/2/btc_usd/trades")
	if err != nil {
		fmt.Printf("%s\r\n", err)
	}
	json_response, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		fmt.Printf("%s\r\n", err)
	}
	resp.Body.Close()
	fmt.Printf("JSON:\r\n%s\r\n", json_response)
	tradeResult := new(TradesResult)
	err = json.Unmarshal(json_response, &tradeResult)
	if err != nil {
		fmt.Printf("%s\r\n", err)
	}
	// Printing trade result first element Amount
	fmt.Printf("Element 0 Amount: %v\r\n", tradeResult[0].Amount)
}

On this line:

tradeResult := new(TradesResult)

You are declaring the tradeResult variable using the *TradeResult type. That is, a pointer to a slice. The error you received is because you can't use index notation on a pointer to a slice.

One way to fix this would be to change the last line to use (*tradeResult)[0].Amount. Alternatively, you could declare tradeResult as:

var tradeResult TradeResult

The json module will be able to decode into &tradeResult just fine, and you won't need to dereference it to index into the slice.