## What is "Dependency Injection" { #what-is-dependency-injection }

**"Dependency Injection"** means, in programming, that there is a way for your code (in this case, your *path operation functions*) to declare things that it requires to work and use: "dependencies".

      "Licensor" shall mean the copyright owner or entity authorized by
      the copyright owner that is granting the License.

      "Legal Entity" shall mean the union of the acting entity and all
      other entities that control, are controlled by, or are under common
      control with that entity. For the purposes of this definition,
      "control" means (i) the power, direct or indirect, to cause the

   * Ideally, this class would have exposed only constructors that require a non-null cause. See
   * https://github.com/jspecify/jspecify-reference-checker/blob/61aafa4ae52594830cfc2d61c8b113009dbdb045/src/main/java/com/google/jspecify/nullness/NullSpecTransfer.java#L789
   * and https://github.com/jspecify/jspecify/issues/490.
   *
   * (That would also have ensured that its cause was always an Error, rather than possibly another

   *     begins. Consider replacing code that creates {@link ListenableFuture}s of closeable types,
   *     including those that pass them to this method, with {@link #submit(ClosingCallable,
   *     Executor)} in order to ensure that resources do not leak. Or, to start a pipeline with a
   *     {@link ListenableFuture} that doesn't create values that should be closed, use {@link
   *     ClosingFuture#from}.
   */

* Why is this change done? What's the use case?
* For user-facing features, what will the API look like?
* What test cases should it have? What could go wrong?
* How will it roughly be implemented? We'll happily provide code pointers to save you time.

We may ask you to answer these questions directly in the GitHub issue or (for large changes) in a shared Google Doc.

      } else if (thisSize < thatMinSize) {
        // this.size() < minSize(that) <= that.size()
        return false; // this.size() < that.size()
      } else { // that can only be a SetView at this point
        int thatSize = 0;
        for (Object unused : that) {
          if (++thatSize > thisSize) {
            return false;
          }
        }
        return true; // that.size() == this.size()
      }

      "Licensor" shall mean the copyright owner or entity authorized by
      the copyright owner that is granting the License.

      "Legal Entity" shall mean the union of the acting entity and all
      other entities that control, are controlled by, or are under common
      control with that entity. For the purposes of this definition,
      "control" means (i) the power, direct or indirect, to cause the

     * <li>If the class loader that loaded the target class can be obtained, that class loader</li>
     * <li>If the class loader that loaded this class can be obtained, that class loader</li>
     * <li>If the system class loader can be obtained, that class loader</li>
     * </ol>
     * <p>

   * Reader#skip(long) skip} to the end of the stream, and return the total number of chars that
   * were skipped.
   *
   * <p>Note that for sources that implement {@link #lengthIfKnown} to provide a more efficient
   * implementation, it is <i>possible</i> that this method will return a different number of chars
   * than would be returned by reading all of the chars.

We could do better.

We can declare a `UserBase` model that serves as a base for our other models. And then we can make subclasses of that model that inherit its attributes (type declarations, validation, etc).

All the data conversion, validation, documentation, etc. will still work as normally.