* Copies all characters between the {@link Readable} and {@link Appendable} objects. Does not
   * close or flush either object.
   *
   * @param from the object to read from
   * @param to the object to write to
   * @return the number of characters copied
   * @throws IOException if an I/O error occurs
   */
  @CanIgnoreReturnValue
  public static long copy(Readable from, Appendable to) throws IOException {

/**
 * Writer that places all output on an {@link Appendable} target. If the target is {@link Flushable}
 * or {@link Closeable}, flush()es and close()s will also be delegated to the target.
 *
 * @author Alan Green
 * @author Sebastian Kanthak
 * @since 1.0
 */
@J2ktIncompatible
@GwtIncompatible
final class AppendableWriter extends Writer {
  private final Appendable target;
  private boolean closed;

  /**

      throw new AssertionError(e);
    }
  }

  private static final Appendable NASTY_APPENDABLE =
      new Appendable() {
        @Override
        public Appendable append(@Nullable CharSequence csq) throws IOException {
          throw new IOException();
        }

        @Override
        public Appendable append(@Nullable CharSequence csq, int start, int end)
            throws IOException {

forceFetch(java.io.File, java.net.URI); } org/gradle/wrapper/Logger.class package org.gradle.wrapper; public final class Logger implements Appendable { public final boolean quiet; public void Logger(boolean); public final void log(String); public final Appendable append(CharSequence); public final Appendable append(CharSequence, int, int); public final Appendable append(char); } org/gradle/wrapper/PathAssembler.class package org.gradle.wrapper; public final class PathAssembler { public void PathAs...

  }

  public <T extends Readable & Appendable> void testMultiBound() {
    assertAssignable(new TypeToken<List<T>>() {}, new TypeToken<List<? extends Readable>>() {});
    assertAssignable(new TypeToken<List<T>>() {}, new TypeToken<List<? extends Appendable>>() {});
  }

  public void testToGenericType() {

  }

  public <T extends Readable & Appendable> void testMultiBound() {
    assertAssignable(new TypeToken<List<T>>() {}, new TypeToken<List<? extends Readable>>() {});
    assertAssignable(new TypeToken<List<T>>() {}, new TypeToken<List<? extends Appendable>>() {});
  }

  public void testToGenericType() {

You can create dependencies that have **sub-dependencies**.

They can be as **deep** as you need them to be.

**FastAPI** will take care of solving them.

## First dependency "dependable" { #first-dependency-dependable }

You could create a first dependency ("dependable") like:

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[8:9] *}

It declares an optional query parameter `q` as a `str`, and then it just returns it.

	// Create test files for further reading.
	for i, appendFile := range appendFiles {
		err = xlStorage.AppendFile(t.Context(), volume, appendFile.fileName, []byte("hello, world"))
		if err != appendFile.expectedErr {
			t.Fatalf("Creating file failed: %d %#v, expected: %s, got: %s", i+1, appendFile, appendFile.expectedErr, err)
		}
	}

	{
		buf := make([]byte, 5)

Let's see a very simple example. It will be so simple that it is not very useful, for now.

But this way we can focus on how the **Dependency Injection** system works.

### Create a dependency, or "dependable" { #create-a-dependency-or-dependable }

Let's first focus on the dependency.

It is just a function that can take all the same parameters that a *path operation function* can take:

* Release Notes: Release Notes (do not translate to "Notas de la Versión")
* Semantic Versioning: Semantic Versioning (do not translate to "Versionado Semántico")
* dependable: dependable (do not translate to "confiable" or "fiable")
* list (as in Python list): list
* context manager: context manager (do not translate to "gestor de contexto" or "administrador de contexto")
* a little bit: un poquito