Go Validators Overview

A validator stores one value and a chain of rules. Pass validators to Is() or Check() to evaluate them and record any failures in a Validation session. If you only need an immediate boolean result, use the standalone functions in the is predicate package.

Name and title

Validator constructors accept the value followed by an optional error path and title:

v.String(value, "company_name", "Company name")

If the name is omitted, Valgo generates value_0, value_1, and so on within the session. If a name is supplied without a title, Valgo humanizes the name for messages: company_name becomes Company name.

generated := v.Is(v.String("").Not().Empty())
named := v.Is(v.String("", "company_name").Not().Empty())
titled := v.Is(v.String("", "company_name", "Customer").Not().Empty())

New() creates an empty validation session and accepts only Options. Use Is() or Check() to evaluate validators.

Not

Not() inverts only the next rule and then resets.

valid := v.Is(v.Number(1).Not().Zero()).Valid() // true

Rule evaluation

Rules are implicitly joined with AND. Is() stops a validator chain after a failure, while Check() continues collecting failures. Use Or() and OrElse() for alternatives; their grouping and short-circuit behavior is documented on the OR Operators page.