printEvent("callStart");
  }

  @Override public void callEnd(Call call) {
    printEvent("callEnd");
  }

  ...
}
```

We can use this listener to race a pair of concurrent HTTP requests:

```java
Request washingtonPostRequest = new Request.Builder()
    .url("https://www.washingtonpost.com/")
    .build();
client.newCall(washingtonPostRequest).enqueue(new Callback() {

    "old key": "old value",
    "second old key": "second old value",
}
new_dict = {**old_dict, "new key": "new value"}
```

Here, `new_dict` will contain all the key-value pairs from `old_dict` plus the new key-value pair:

```Python
{
    "old key": "old value",
    "second old key": "second old value",
    "new key": "new value",
}
```

import okio.Buffer
import okio.ForwardingSink
import okio.ForwardingSource
import okio.Sink
import okio.Source
import okio.buffer

/**
 * Transmits a single HTTP request and a response pair. This layers connection management and events
 * on [ExchangeCodec], which handles the actual I/O.
 */
class Exchange(
  internal val call: RealCall,
  internal val eventListener: EventListener,

}

// Status describes the current state of a KMS.
type Status struct {
	Online  map[string]struct{}
	Offline map[string]Error
}

// DEK is a data encryption key. It consists of a
// plaintext-ciphertext pair and the ID of the key
// used to generate the ciphertext.
//
// The plaintext can be used for cryptographic
// operations - like encrypting some data. The
// ciphertext is the encrypted version of the

As part of that, I needed to investigate, test and use many alternatives.

The history of **FastAPI** is in great part the history of its predecessors.

As said in the section [Alternatives](alternatives.md){.internal-link target=_blank}:

<blockquote markdown="1">

**FastAPI** wouldn't exist if not for the previous work of others.

  /**
   * Returns a new equivalence relation for {@code F} which evaluates equivalence by first applying
   * {@code function} to the argument, then evaluating using {@code this}. That is, for any pair of
   * non-null objects {@code x} and {@code y}, {@code equivalence.onResultOf(function).equivalent(a,
   * b)} is true if and only if {@code equivalence.equivalent(function.apply(a), function.apply(b))}
   * is true.
   *

      if (result == null) result = ArrayList(2)
      result.add(value(i))
    }
  }
  return result?.toList().orEmpty()
}

internal fun Headers.commonIterator(): Iterator<Pair<String, String>> {
  return Array(size) { name(it) to value(it) }.iterator()
}

internal fun Headers.commonNewBuilder(): Headers.Builder {
  val result = Headers.Builder()
  result.namesAndValues += namesAndValues

        get() = (this as? NodeWithAnnotations<*>)?.annotations?.any { it.nameAsString == "Incubating" } ?: false

    private
    fun CompilationUnit.toVersionIncubating(sourceFile: File, node: Node) =
        Pair(
            (node as? NodeWithJavadoc<*>)?.javadoc?.orElse(null)?.let { findVersionFromJavadoc(it) }
                // This is needed to find the JavaDoc of a package declaration in 'package-info.java'

  // Required.
  optional string type = 1;
}

// FlowSchema defines the schema of a group of flows. Note that a flow is made up of a set of inbound API requests with
// similar attributes and is identified by a pair of strings: the name of the FlowSchema and a "flow distinguisher".
message FlowSchema {
  // `metadata` is the standard object's metadata.

				// both 1st operand and 3rd operand are (Rs, Rs+1) register pair.
				// And the register pair must be contiguous.
				if (a[0].Type != obj.TYPE_REGREG) || (a[2].Type != obj.TYPE_REGREG) {
					p.errorf("invalid addressing modes for 1st or 3rd operand to %s instruction, must be register pair", op)
					return
				}
				// For ARM64 CASP-like instructions, its 2nd destination operand is register pair(Rt, Rt+1) that can