使用正确的返回类型正确解组不确定的JSON

I am working with a JSON API to pull forex quotes.

I am unmarshaling to a struct like so:

type Quote struct {
    Symbol string
    Bid float32
    Ask float32
    Price float32
    Timestamp int
}

Using a function like so:

func GetQuotes(symbols []string, api_key string) []Quote {
    result := fetch("quotes?pairs=" + strings.Join(symbols, ","), api_key)

    quotes := []Quote{}

    e := json.Unmarshal(result, &quotes)

    if e != nil {
        log.Fatal(e)
    }

    return quotes
}

My issue is: If I get back an error such as "The data you've requested is not available", how do I properly return the correct type from GetQuotes?

If I unmarshal using json.RawMessage I can use a switch to chose the proper struct, such as Quote or ErrorMessage, however, then I cannot set a proper return type from GetQuotes

I suggest you to follow the Go way, and return both error and Quotes, here is an example:

func GetQuotes(symbols []string, api_key string) ([]Quote, error) {        
    quotes := []Quote{}
    // A better would be if the fetch 
    // fuction also returns both 
    // result and error
    result := fetch("quotes?pairs=" + strings.Join(symbols, ","), api_key)

    e := json.Unmarshal(result, &quotes)

    if e != nil {
        return quotes, e
    }

    return quotes, nil
}

Now you can check if request or marshaling returns an error.

quotes, err := GetQuotes(symbols, apiKey)
if err != nil {
  // handle errors here
}

You can also return the ErrorMessage type your custom struct instead of error.

_{Error handling and Go}

In order to returns different types, you must use an interface in the return statement, here is an example:

package main

import (
    "fmt"
)

type Foo struct {}

type Bar struct {}

func Baz(w string) interface{} {
  if w == "Foo" {
    return Foo{}
  }
  return Bar{}
}

func main() {
    fmt.Printf("%T", Baz("Bar"))
}
=> main.Bar

The Baz function able to returns both Foo and Bar structs.