result — payload + error wrapper

github.com/go-composites/result (Go package Result, imported from the src/ sub-directory) is the org's return-value wrapper. Instead of returning (value, error) Go-style, methods across go-composites return a single Result.Interface carrying both a payload and an error.

API

import Result "github.com/go-composites/result/src"

type Interface interface {
    Payload() interface{}
    HasError() bool
    Error() Error.Interface
}

func New(options ...Option) Interface
func WithPayload(payload interface{}) Option
func WithError(error Error.Interface) Option

A fresh Result.New() defaults its payload to Null.New() and its error to the null error, so neither accessor ever returns a bare nil.

r := Result.New(Result.WithPayload(42))
r.Payload() // 42
r.Error()   // the null error (IsNull() == true)

Member	Behaviour
Payload()	Returns the stored payload; defaults to a non-nil Null value.
Error()	Returns the stored error; defaults to the null error.
HasError()	true iff a real error is attached, i.e. !d.error.IsNull().

HasError()

HasError() is defined as:

func (d data) HasError() bool {
    return !d.error.IsNull()
}

Because the null error reports IsNull() == true, a Result with no error reports HasError() == false, while a Result carrying a real error reports HasError() == true — exactly what the name implies.

Result.New().HasError()                                   // false (no error)
Result.New(Result.WithError(Error.New("x"))).HasError()   // true  (has error)

The idiomatic guard

Across the org, callers branch on the result with the natural shape:

if r := s.Split(" "); r.HasError() {
    fmt.Println(r.Error().Message()) // failure path
} else {
    use(r.Payload())                 // success path
}

Construction

New is variadic over functional options:

• WithPayload(v) installs v as the payload.
• WithError(e) installs e as the error.

Options are applied in order over the Null/null-error defaults, so a Result.New() with no options is a successful, empty result.

Dependencies

result depends on error (including the null-error sentinel) and null.