Collection<F> fromCollection, Function<? super F, T> function) {
    return new TransformedCollection<>(fromCollection, function);
  }

  private static final class TransformedCollection<
          F extends @Nullable Object, T extends @Nullable Object>
      extends AbstractCollection<T> {
    final Collection<F> fromCollection;
    final Function<? super F, ? extends T> function;

          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction) {
    return CollectCollectors.toImmutableMap(keyFunction, valueFunction);
  }

  public static <T extends @Nullable Object, K, V>
      Collector<T, ?, ImmutableMap<K, V>> toImmutableMap(
          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction,

Then you can create another dependency function (a "dependable") that at the same time declares a dependency of its own (so it is a "dependant" too):

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[13] *}

Let's focus on the parameters declared:

* Even though this function is a dependency ("dependable") itself, it also declares another dependency (it "depends" on something else).

## Description from docstring { #description-from-docstring }

As descriptions tend to be long and cover multiple lines, you can declare the *path operation* description in the function <dfn title="a multi-line string as the first expression inside a function (not assigned to any variable) used for documentation">docstring</dfn> and **FastAPI** will read it from there.

As an example, let's take this function:

```python
from typing import Optional


def say_hi(name: Optional[str]):
    print(f"Hey {name}!")
```

The parameter `name` is defined as `Optional[str]`, but it is **not optional**, you cannot call the function without the parameter:

```Python
say_hi()  # Oh, no, this throws an error! 😱
```

Test için bir dependency'yi override etmek istediğinizde, key olarak orijinal dependency'yi (bir function), value olarak da override edecek dependency'nizi (başka bir function) verirsiniz.

Böylece **FastAPI**, orijinal dependency yerine bu override'ı çağırır.

{* ../../docs_src/dependency_testing/tutorial001_an_py310.py hl[26:27,30] *}

/// tip | İpucu

    return null;
  }

  @Override
  public Set<T> asSet() {
    return Collections.emptySet();
  }

  @Override
  public <V> Optional<V> transform(Function<? super T, V> function) {
    checkNotNull(function);
    return Optional.absent();
  }

  @Override
  public boolean equals(@Nullable Object obj) {
    return this == obj;
  }

  @Override
  public int hashCode() {

	"sync/atomic"
)

// Inspired from Golang sync.Once but it is only marked
// initialized when the provided function returns nil.

// Init represents the structure.
type Init struct {
	done uint32
	m    sync.Mutex
}

// Do is similar to sync.Once.Do - makes one successful
// call to the function. ie, it invokes the function
// if it is not successful yet.
func (l *Init) Do(f func() error) error {

	"testing.Main(",
	"testing.tRunner(",
	"testing.tRunner(",
	"runtime.goexit",
	"created by runtime.gc",
	// ignore the snapshot function.
	// since the snapshot is taken here the entry will have the current function too.
	"pickRelevantGoroutines",
	"runtime.MHeap_Scavenger",
	"signal.signal_recv",
	"sigterm.handler",
	"runtime_mcall",
	"goroutine in C code",
}

{* ../../docs_src/dependencies/tutorial008e_an_py310.py hl[12,16] *}

`Depends()` принимает параметр `scope`, который может быть: