Input Validator Lab

In this lab you will build an input validation system that uses a custom error type to carry structured field-level error information.

Your Task

1. Define ValidationError

Implement Error() string so it returns:

For example: field email: must contain @

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2. Implement validateEmail(s string) error

• The email must contain @
• There must be at least one . after the @
• Return a ValidationError with Field: "email" if either check fails
• Return nil if the email is valid

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3. Implement validatePassword(s string) error

• The password must be at least 8 characters long
• The password must contain at least one digit (0–9)
• Return a ValidationError with Field: "password" if either check fails
• Return nil if the password is valid

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4. Implement validateAge(n int) error

• The age must be greater than 0 and less than 150
• Return a ValidationError with Field: "age" if the check fails
• Return nil if the age is valid

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5. Implement ValidateAll(email, password string, age int) []error

• Run all three validators
• Collect every non-nil error into a []error slice
• Return the slice (it may be empty if all inputs are valid)

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Expected Behavior

Hint: use strings.Contains to check for @ and ., and a loop over the password rune-by-rune (or with strings.ContainsAny) to detect digits.