Marshalling JSON

encoding/json turns Go values into JSON with one function:

data, err := json.Marshal(v)   // data is a []byte

It works by reflection, walking v at run time and writing the bytes as it goes. That single fact explains almost everything else about the package.

Only exported fields exist

Reflection cannot read a field it is not allowed to name, so an unexported field is invisible: it is never written, and never filled in when decoding. There is no tag that changes it. If a value has to cross the JSON boundary, its field starts with a capital letter.

With no tags at all, the key is the Go field name verbatim - "Title", not "title". Renaming is the next challenge; this one is about what happens before you reach for a tag.

What each Go type becomes

Two of those rows are the ones that bite. A map's keys are sorted by the encoder, so encoding the same map twice gives byte-identical output even though ranging over it would not. And a nil slice is null while an empty slice is [] - the same distinction Go draws, carried through to the wire and all the way to whoever consumes it.

Indenting

json.MarshalIndent takes a prefix and an indent, and is Marshal plus line breaks. The prefix goes in front of every line after the first, and the indent is one level. Two spaces and no prefix is the usual choice:

json.MarshalIndent(v, "", "  ")

Neither function adds a trailing newline.

Angle brackets come back escaped

Marshal escapes <, > and & as \u003c, \u003e and \u0026, so the output is safe to paste inside a <script> tag. It is the same string once decoded, so this only matters when you are comparing raw bytes - which the tests here do.

The error is not decoration

Most values encode, but not all. A channel, a function or a complex number has no JSON representation, and a value that reaches itself makes the encoder stop rather than recurse forever. All three come back as an error, which is why Marshal returns one.

Task

Implement EncodeTask, EncodeIndented, EncodeAll, EncodeCounts and CanEncode.

Hints

• json.Marshal gives you a []byte; the functions here return a string, so convert with string(data).
• On an error, return "" and the error. Do not return the partial bytes.
• EncodeAll(nil) should come out as null and EncodeAll([]Task{}) as [] - you get both for free by passing the slice straight through.
• CanEncode is one call and one comparison: marshal, discard the bytes with _, and report whether the error was nil.