guard_clauses

Description:

guard clauses

Guard Clauses #
A dart port of the excellent C# Guard Clauses package by Ardalis.
A simple extensible package with guard clause extensions.
A guard clause is a software pattern that simplifies complex functions by "failing fast", checking for invalid inputs up front and immediately failing if any are found.
Usage #
void processOrder(Order? order)
{
Guard.against.nullValue(order, 'order');

// process order here
}

// OR

class Order
{
String _name;
int _quantity;
double _max;
double _unitPrice;

Order(String name, int quantity, double max, double unitPrice) {
_name = Guard.against.nullOrWhiteSpace(name);
_quantity = Guard.against.negativeOrZero(quantity);
_max = Guard.against.zero(max);
_unitPrice = Guard.against.negative(unitPrice);
}
}
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Supported Guard Clauses #

Guard.against.invalidInput (throws if predicate expression returns false)
Guard.against.invalidFormat (throws if the input string doesn't match the provided regex)
Guard.against.negative (throws if the input is negative)
Guard.against.negativeOrZero (throws if the input is negative or zero)
Guard.against.nullValue (throws if input is null)
Guard.against.nullOrEmpty (throws if string input is null or empty)
Guard.against.nullOrEmptyCollection (throws if the input collection is null or empty)
Guard.against.nullOrWhiteSpace (throws if string input is null, empty or whitespace)
Guard.against.nullOrInvalidInput (throws if input is null, or predicate expression returns false)
Guard.against.indexOutOfRange (throws if input is not a valid index)
Guard.against.outOfRangeItems (throws if any values in the input collection are outside the provided range)
Guard.against.outOfRange (throws if the input collection is outside the provided range)
Guard.against.zero (throws if number input is zero)

Extending with your own Guard Clauses #
To extend by creating your own guard clauses, create a new extension class for Guard.
extension GuardExtensions on Guard {
/// Throws an ArgumentError if [input] is 'foo'.
/// Returns [input] otherwise.
String foo(String input, {String? name}) {
if (input.toLowerCase()) {
throw ArgumentError.value(input, name);
}

return input;
}
}

// Usage
void sumpin(String otherSumpin) {
Guard.against.foo(otherSumpin);
...
}
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References #
The references are C#-centric but the concepts apply well.

Getting Started with Guard Clauses
How to write clean validation clauses in .NET (Nick Chapsas, YouTube, 9 minutes)
Guard Clauses (podcast: 7 minutes)
Guard Clause