42 lines
1.7 KiB
Go
42 lines
1.7 KiB
Go
 
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// Package validate provides small, composable value validators.
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//
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// A validator is just a func(T) error: it returns nil when the value is
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// acceptable, or an error describing the problem. Nothing has to implement
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// an interface, so a plain closure works anywhere a validator is expected.
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// Combine validators with [All] (stop at the first failure) or [Collect]
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// (run them all and join every failure).
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//
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// username := validate.All(
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// validate.MinLength(3),
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// validate.MaxLength(16),
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// validate.Chars("abcdefghijklmnopqrstuvwxyz0123456789_"),
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// )
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// if err := username(input); err != nil {
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// // errors.Is(err, validate.ErrDisallowedChars) still works here
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// }
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//
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// Errors are plain sentinel values (see [Error]); match them with
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// errors.Is. [Err] matches any error produced by this package.
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//
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// # Comparison with other packages
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//
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// - go-playground/validator drives validation from struct tags and
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// reflection.
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// - go-ozzo/ozzo-validation composes rules in code, but through a Rule
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// interface over interface{}.
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// - asaskevich/govalidator is a bag of IsX string helpers.
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//
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// This package is the code-composition style with two constraints kept
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// deliberately: validators are ordinary generic functions, checked by the
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// compiler with no reflection ([In], [Equal] and the rest will not accept
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// the wrong type), and there are no dependencies outside the standard
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// library.
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//
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// # When to use something else
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//
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// Reach for go-playground/validator if you want struct-tag validation,
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// translated messages, or a large catalogue of built-in checks. This
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// package stays small and leaves struct/field wiring and error
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// presentation to the caller.
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package validate
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