json unmarshal string or number to float64

[Michael Daffin]

I has some json input that normally contains a string quoted float value but also some times take on the value of -1.

Example: https://play.golang.org/p/1HpulGMABQ

If I use 

Value float64 `json:"value"`

it errors with "json: cannot unmarshal string into Go value of type float64" for js1 and if I use

Value float64 `json:"value,string"`

it errors with "json: invalid use of ,string struct tag, trying to unmarshal unquoted value into [34 118 97 108 117 101 34]%!(EXTRA *reflect.rtype=main.R)" for js2.

What is the best way to convert both cases into float64 (or even the -1 to nil).

Note that this is happening for several values in a larger nested data structure so I want to avoid, if at all possible, copying all the values from interface{} into a new data structure of the correct types or casting interface{} every time I want to access the values.

Thank you

[Ian Davis]

You could use a custom type and implement the UnmarshalJSON interface for it. Something like:

http://play.golang.org/p/5f-Lob70HU

Ian