proposal: encoding/json: fluent interface for SetIndent/SetEscapeHTML

[xrfang]

In the stdlib, it's defined as:

func (enc *Encoder) SetIndent(prefix, indent string) {
    enc.indentPrefix = prefix
        enc.indentValue = indent
}

I suggest to make it fluent by:

func (enc *Encoder) SetIndent(prefix, indent string) *Encoder {
        enc.indentPrefix = prefix
        enc.indentValue = indent
        return enc
}

So that it is more convenient to do this:

json.NewEncoder(os.Stdout).SetIndent("", "    ").Encode(data)

[ianlancetaylor]

Changing the method signature at this point would break the Go 1 compatibility guarantee (https://golang.org/doc/go1compat).

As a pure style point, Go code tends to use fluent interfaces less than in some other languages, in part because fluent interfaces don't work in Go for functions/methods that need to return errors.

[xrfang]

OK, I am curious why this would break compatiblity?

If a function returns 1 variable, you now return 2, or none, that's a break of compatibility, but if the function originally returns nothing, now you return one (or any more) that will not affect any existing code?

[ianlancetaylor]

This currently valid Go program would stop compiling.

package p

import "encoding/json"

var F func(*json.Encoder, string, string) = (*json.Encoder).SetIndent

[rsc]

This breaks compatibility, and it's not worth adding a second API.