Remove Go 1.18 build tags

Go 1.19 has been the minimum required version
since Go 1.20 was released.
With the release of Go 1.21, even Go 1.19 is unsupported.
There's no reason specialize for versions before Go 1.18 anymore.

This deletes the Go 1.18 build-tagged files
and merges their contents into their siblings.

array.go

@@ -21,6 +21,7 @@
 package zap
 
 import (
+	"fmt"
 	"time"
 
 	"go.uber.org/zap/zapcore"
@@ -94,11 +95,137 @@ func Int8s(key string, nums []int8) Field {
 	return Array(key, int8s(nums))
 }
 
+// Objects constructs a field with the given key, holding a list of the
+// provided objects that can be marshaled by Zap.
+//
+// Note that these objects must implement zapcore.ObjectMarshaler directly.
+// That is, if you're trying to marshal a []Request, the MarshalLogObject
+// method must be declared on the Request type, not its pointer (*Request).
+// If it's on the pointer, use ObjectValues.
+//
+// Given an object that implements MarshalLogObject on the value receiver, you
+// can log a slice of those objects with Objects like so:
+//
+//	type Author struct{ ... }
+//	func (a Author) MarshalLogObject(enc zapcore.ObjectEncoder) error
+//
+//	var authors []Author = ...
+//	logger.Info("loading article", zap.Objects("authors", authors))
+//
+// Similarly, given a type that implements MarshalLogObject on its pointer
+// receiver, you can log a slice of pointers to that object with Objects like
+// so:
+//
+//	type Request struct{ ... }
+//	func (r *Request) MarshalLogObject(enc zapcore.ObjectEncoder) error
+//
+//	var requests []*Request = ...
+//	logger.Info("sending requests", zap.Objects("requests", requests))
+//
+// If instead, you have a slice of values of such an object, use the
+// ObjectValues constructor.
+//
+//	var requests []Request = ...
+//	logger.Info("sending requests", zap.ObjectValues("requests", requests))
+func Objects[T zapcore.ObjectMarshaler](key string, values []T) Field {
+	return Array(key, objects[T](values))
+}
+
+type objects[T zapcore.ObjectMarshaler] []T
+
+func (os objects[T]) MarshalLogArray(arr zapcore.ArrayEncoder) error {
+	for _, o := range os {
+		if err := arr.AppendObject(o); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// ObjectMarshalerPtr is a constraint that specifies that the given type
+// implements zapcore.ObjectMarshaler on a pointer receiver.
+type ObjectMarshalerPtr[T any] interface {
+	*T
+	zapcore.ObjectMarshaler
+}
+
+// ObjectValues constructs a field with the given key, holding a list of the
+// provided objects, where pointers to these objects can be marshaled by Zap.
+//
+// Note that pointers to these objects must implement zapcore.ObjectMarshaler.
+// That is, if you're trying to marshal a []Request, the MarshalLogObject
+// method must be declared on the *Request type, not the value (Request).
+// If it's on the value, use Objects.
+//
+// Given an object that implements MarshalLogObject on the pointer receiver,
+// you can log a slice of those objects with ObjectValues like so:
+//
+//	type Request struct{ ... }
+//	func (r *Request) MarshalLogObject(enc zapcore.ObjectEncoder) error
+//
+//	var requests []Request = ...
+//	logger.Info("sending requests", zap.ObjectValues("requests", requests))
+//
+// If instead, you have a slice of pointers of such an object, use the Objects
+// field constructor.
+//
+//	var requests []*Request = ...
+//	logger.Info("sending requests", zap.Objects("requests", requests))
+func ObjectValues[T any, P ObjectMarshalerPtr[T]](key string, values []T) Field {
+	return Array(key, objectValues[T, P](values))
+}
+
+type objectValues[T any, P ObjectMarshalerPtr[T]] []T
+
+func (os objectValues[T, P]) MarshalLogArray(arr zapcore.ArrayEncoder) error {
+	for i := range os {
+		// It is necessary for us to explicitly reference the "P" type.
+		// We cannot simply pass "&os[i]" to AppendObject because its type
+		// is "*T", which the type system does not consider as
+		// implementing ObjectMarshaler.
+		// Only the type "P" satisfies ObjectMarshaler, which we have
+		// to convert "*T" to explicitly.
+		var p P = &os[i]
+		if err := arr.AppendObject(p); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // Strings constructs a field that carries a slice of strings.
 func Strings(key string, ss []string) Field {
 	return Array(key, stringArray(ss))
 }
 
+// Stringers constructs a field with the given key, holding a list of the
+// output provided by the value's String method
+//
+// Given an object that implements String on the value receiver, you
+// can log a slice of those objects with Objects like so:
+//
+//	type Request struct{ ... }
+//	func (a Request) String() string
+//
+//	var requests []Request = ...
+//	logger.Info("sending requests", zap.Stringers("requests", requests))
+//
+// Note that these objects must implement fmt.Stringer directly.
+// That is, if you're trying to marshal a []Request, the String method
+// must be declared on the Request type, not its pointer (*Request).
+func Stringers[T fmt.Stringer](key string, values []T) Field {
+	return Array(key, stringers[T](values))
+}
+
+type stringers[T fmt.Stringer] []T
+
+func (os stringers[T]) MarshalLogArray(arr zapcore.ArrayEncoder) error {
+	for _, o := range os {
+		arr.AppendString(o.String())
+	}
+	return nil
+}
+
 // Times constructs a field that carries a slice of time.Times.
 func Times(key string, ts []time.Time) Field {
 	return Array(key, times(ts))