A tuple is a finite, ordered group of values treated as one entity. It is useful when a function needs to return related results, such as a success status and an error message, without adding multiple arguments. section 4.2
Returning validation results
A validation function can return a tuple such as (false, 'Input is too long!'). In JavaScript, the same idea can use a custom Tuple type: `const Status = Tuple(Boolean, String);` and return `new Status(false, 'Invalid input!')`. The tuple keeps the values ordered, immutable, and available as one result. section 4.2
Listing 4.2. Typed Tuple data type
const Tuple = function( /* types */ ) {
const typeInfo = Array.prototype.slice.call(arguments, 0); #1
const _T = function( /* values */ ) { #2
const values = Array.prototype.slice.call(arguments, 0); #3
if(values.some((val) => #4
val === null || val === undefined)) {
throw new ReferenceError('Tuples may not have
any null values');
}
if(values.length !== typeInfo.length) { #5
throw new TypeError('Tuple arity does not
match its prototype');
}
values.map(function(val, index) { #6
this['_' + (index + 1)] = checkType(typeInfo[index])(val);
}, this);
Object.freeze(this); #7
};
_T.prototype.values = function() { #8
return Object.keys(this).map(function(k) {
return this[k];
}, this);
};
return _T;
};
Inspect the typed JavaScript Tuple implementation, including arity checks, null-value rejection, type checks, and freezing. section 4.2
