Features.md

Automatic message generation

Guava's API forces you to repeat yourself. This API generates concise messages on your behalf.

Guava:

String name = "John Smith";
Preconditions.checkArgument(name.length() <= 5, "name must be shorter than 6 characters");

Output:

java.lang.IllegalArgumentException: name must be shorter than 6 characters
  at com.google.common.base.Preconditions.checkArgument(Preconditions.java:146)
  at Main.guava(Main.java:45)
  at Main.main(Main.java:70)

This API:

requireThat(name, "Name").length().isLessThanOrEqualTo(5);

Output:

java.lang.IllegalArgumentException: name may not contain more than 5 characters.
Name.length(): 7
Name         : John Smith
  at Main.requirements(Main.java:57)
  at Main.main(Main.java:72)

Diffs provided whenever possible

Not only do we provide you with the actual and expected values, we also provide a diff whenever possible.

Guava:

List<Integer> actual = Arrays.asList(2, 3, 4, 6);
List<Integer> expected = Arrays.asList(1, 3, 5);
Preconditions.checkArgument(actual.containsAll(expected), "actual must contain %s", expected);

Output:

java.lang.IllegalArgumentException: actual must contain [1, 3, 5]
  at com.google.common.base.Preconditions.checkArgument(Preconditions.java:146)
  at Main.guava(Main.java:95)
  at Main.run(Main.java:129)
  at Main.main(Main.java:137)

This API:

List<Integer> actual = Arrays.asList(2, 3, 4, 6);
List<Integer> expected = Arrays.asList(1, 3, 5);
requireThat(actual, "Actual").containsAll(expected);

Output:

java.lang.IllegalArgumentException: actual must contain all elements in: [1, 3, 5]
Actual : [2, 3, 4, 6]
Missing: [1, 5]
  at Main.requirements(Main.java:106)
  at Main.run(Main.java:131)
  at Main.main(Main.java:137)

Clean stack-traces

This API's classes do not show up in your stack-traces.

Guava:

java.lang.NullPointerException: Actual may not be null
  at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:251)
  at Main.guava(Main.java:21)
  at Main.main(Main.java:65)

This API:

java.lang.NullPointerException: Actual may not be null
  at Main.requirements(Main.java:33)
  at Main.main(Main.java:67)

Assertion support

This library is compatible with the assert keyword.

If you need to run in a high performance, zero allocation environment (to reduce latency and jitter) look no further than the following design pattern:

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.Month;

public class Person
{
  public void eatLunch()
  {
    assert assumeThat("time", LocalDateTime.now().getHour()).isAfter("noon", 12).elseThrow();
  }
}

Per https://docs.oracle.com/javase/8/docs/technotes/guides/language/assert.html:

Disabling assertions eliminates their performance penalty entirely.

Multiple validation failures

String name = "George";
String province = "Florida";
List<String> provinces = Arrays.asList("Ontario", "Quebec", "Nova Scotia", "New Brunswick", "Manitoba",
  "British Columbia", "Prince Edward Island", "Saskatchewan", "Alberta", "Newfoundland and Labrador");

List<ValidationFailure> failures = new ArrayList<>();
failures.addAll(checkIf(name, "name").length().isBetween(10, 30).elseGetFailures();
failures.addAll(checkIf(provinces, "provinces").contains(province).elseGetFailures());

for (ValidationFailure failure: failures)
  System.out.println(failure.getMessage());

Output will look like:

name must contain [10, 30) characters.

"provinces" must contain provide "province".
province: Florida
Actual: [Ontario, Quebec, Nova Scotia, New Brunswick, Manitoba, British Columbia, Prince Edward Island, Saskatchewan, Alberta, Newfoundland and Labrador]

Nested validations

Nested validations facilitate checking multiple properties of a value. For example, given

Map<String, Integer> nameToAge = new HashMap<>();
nameToAge.put("Leah", 3);
nameToAge.put("Nathaniel", 1);

To validate that nameToAge has the keys "Leah" and "Nathaniel" and the values 3 and 1, you can write:

requireThat(nameToAge, "nameToAge").
  apply(v -> v.keySet().containsAll(Arrays.asList("Leah", "Nathaniel"))).
  apply(v -> v.values().containsAll(Arrays.asList(3, 1)));

instead of:

requireThat(nameToAge, "nameToAge").
  keySet().containsAll(Arrays.asList("Leah", "Nathaniel"));

requireThat(nameToAge, "nameToAge").
  values().containsAll(Arrays.asList(3, 1));

String diff

When a String comparison fails, the library outputs a diff of the values being compared.

Depending on the terminal capability, you will see a Textual or a colored diff.

On Windows OS, this feature only works in Windows Terminal. On other platforms, it should work in any terminal.

Overriding Terminal Detection

The use of colors is disabled by default if stdin or stdout are redirected, even if ANSI colors are supported. To enable colors, invoke GlobalConfiguration.terminalEncoding(TerminalEncoding).

Returning the value after validation

You can get the value after validating or transforming it, e.g.

class Player
{
  private final String name;

  public Player(String name)
  {
    this.name = requireThat(name, "name").strip().isNotEmpty().getValue();
  }
}