import {Predicate} from 'tiny-types/lib/predicates/Predicate'

public class | source

Predicate

Direct Subclass:

src/predicates/Predicate.ts~SingleConditionPredicate

Describes a Condition that the value should meet.

To define a custom predicate to be used with the check function you can either extend the Predicate, or use the Predicate.to factory method.

Example:

Assuming we'd like to create an isDefined() predicate:

ensure(`some value`, value, isDefined());

We can either use the Predicate.to factory method:


import { Predicate } from 'tiny-types';

function isDefined<T>(): Predicate<T> {
    return Predicate.to(`be defined`, (value: T) =>
        ! (value === null || value === undefined),
    );
}

or extend the Predicate itself


import { Predicate, Result, Success, Failure } from 'tiny-types';

function isDefined<T>() {
  return new IsDefined<T>();
}

class IsDefined<T> extends Predicate<T> {
    check(value: T): Result<T> {
      return ! (value === null || value === undefined)
        ? new Success(value)
        : new Failure(value, `be defined`);
    }
}

Static Method Summary

Static Public Methods
public static	to(description: string, condition: Condition<V>): Predicate<V> A factory method instantiating a single-condition predicate.

Static Public Methods

public static to(description: string, condition: Condition<V>): Predicate<V> source

A factory method instantiating a single-condition predicate. You can use it instead of extending the {Predicate} to save some keystrokes.

Params:

Name	Type	Attribute	Description
description	string		The description of the condition is used by check to generate the error message. The description should be similar to`be defined`, `be less than some value` for the error message to make sense.
condition	Condition<V>		a function that takes a value of type `V` and returns a boolean indicating whether or not the condition is met. For example: `(value: V) => !! value`

Return:

Predicate<V>

Example:

Predicate.to(`be defined`, (value: T) => ! (value === null || value === undefined));