assertThat(expected).hasMessageThat().contains("connected");

    // adjacent below
    assertEquals(Range.closedOpen(4, 4), range.intersection(Range.closedOpen(2, 4)));

    // overlap below
    assertEquals(Range.closed(4, 6), range.intersection(Range.closed(2, 6)));

    // enclosed with same start
    assertEquals(Range.closed(4, 6), range.intersection(Range.closed(4, 6)));

* Missing null checks may cause NullPointerException
* Bridging with Kotlin code is polluted with platform types
* Some public APIs have incorrect nullability annotations (both overly restrictive and overly permissive)

While there are competing ways to represent absence (`Optional`, "Null Object" pattern, method overloads),
it is unlikely that we'll be able to remove `null` entirely.

   * Overlapping ranges and empty ranges are forbidden, though adjacent ranges are permitted and
   * will be merged.
   *
   * @throws IllegalArgumentException if any ranges overlap or are empty
   * @since 21.0
   */
  public static <C extends Comparable<?>> ImmutableRangeSet<C> copyOf(Iterable<Range<C>> ranges) {
    return new ImmutableRangeSet.Builder<C>().addAll(ranges).build();
  }

    assertThat(expected).hasMessageThat().contains("connected");

    // adjacent below
    assertEquals(Range.closedOpen(4, 4), range.intersection(Range.closedOpen(2, 4)));

    // overlap below
    assertEquals(Range.closed(4, 6), range.intersection(Range.closed(2, 6)));

    // enclosed with same start
    assertEquals(Range.closed(4, 6), range.intersection(Range.closed(4, 6)));

   * Overlapping ranges and empty ranges are forbidden, though adjacent ranges are permitted and
   * will be merged.
   *
   * @throws IllegalArgumentException if any ranges overlap or are empty
   * @since 21.0
   */
  public static <C extends Comparable<?>> ImmutableRangeSet<C> copyOf(Iterable<Range<C>> ranges) {
    return new ImmutableRangeSet.Builder<C>().addAll(ranges).build();
  }

Also, the best approach was to use already existing standards.

So, before even starting to code **FastAPI**, I spent several months studying the specs for OpenAPI, JSON Schema, OAuth2, etc. Understanding their relationship, overlap, and differences.

## Design { #design }

Then I spent some time designing the developer "API" I wanted to have as a user (as a developer using FastAPI).

// The copy built-in function copies elements from a source slice into a
// destination slice. (As a special case, it also will copy bytes from a
// string to a slice of bytes.) The source and destination may overlap. Copy
// returns the number of elements copied, which will be the minimum of
// len(src) and len(dst).
func copy(dst, src []Type) int

// The delete built-in function deletes the element with the specified key

	case obj.TYPE_CONST, obj.TYPE_FCONST, obj.TYPE_SCONST, obj.TYPE_ADDR:
		// OK
	default:
		p.errorf("DATA value must be an immediate constant or address")
		return
	}

	// The addresses must not overlap. Easiest test: require monotonicity.
	if lastAddr, ok := p.dataAddr[name]; ok && nameAddr.Offset < lastAddr {
		p.errorf("overlapping DATA entry for %s", name)
		return
	}
	p.dataAddr[name] = nameAddr.Offset + int64(sz)

// listSem is a semaphore restricting concurrent invocations of 'go list'. 'go
// list' has its own internal concurrency, so we use a hard-coded constant (to
// allow the I/O-intensive phases of 'go list' to overlap) instead of scaling
// all the way up to GOMAXPROCS.
var listSem = make(chan semToken, 2)

type semToken struct{}

// loadImports populates w with information about the packages in the standard

Kubernetes now allows users to define the cluster Service CIDR via an API object: ServiceCIDR.