Required / Optional prop definition by name

main.ts

type RequiredPropName<T extends string> = `${T}!`
type OptionalPropName<T extends string> = `${T}?`

type QualifiedPropName<T extends string> = RequiredPropName<T> | OptionalPropName<T>

type RequiredProp<T> = {
    value: T,
    required: true
}
type OptionalProp<T> = {
    value: T,
    required: false
}

type QualifiedProp<T> = RequiredProp<T> | OptionalProp<T>

const b = <
PropNameWithQualifier,
PropName extends string,
ReturnValue extends PropNameWithQualifier extends RequiredPropName<PropName> ? RequiredProp<PropName> : OptionalProp<PropName>
>(arg: PropNameWithQualifier & QualifiedPropName<PropName>): ReturnValue => {
    const qualifier = arg[-1]

    return {
        value: arg.slice(0, -1),
        required: qualifier === '!'
    } as ReturnValue
}

const props = {
    id: b('id!'),
    name: b('name!'),
    sex: b('sex?'),
    age: b('age?'),
}

props