def append_song(result, song)
# test we're given the right parameters
unless result.kind_of?(String)
fail TypeError.new("String expected") end
unless song.kind_of?(Song)
fail TypeError.new("Song expected")
end
result << song.title << " (" << song.artist << ")" end
result = ""
append_song(result, song) # => "I Got Rhythm (Gene Kelly)"
采用Ruby的鸭子输入，您可以编写一些简单得多的东西:
def append_song(result, song)
result << song.title << " (" << song.artist << ")"
end
result = ""
append_song(result, song) # => "I Got Rhythm (Gene Kelly)"
interface StorageInterface
{
public function write(string $key, array $value): bool;
public function read(string $key): array;
}
class File implements StorageInterface
{
public function read(string $key): array {
//reading from a file
}
public function write(string $key, array $value): bool {
//writing in a file implementation
}
}
class Session implements StorageInterface
{
public function read(string $key): array {
//reading from a session
}
public function write(string $key, array $value): bool {
//writing in a session implementation
}
}
class Storage implements StorageInterface
{
private $_storage = null;
function __construct(StorageInterface $storage) {
$this->_storage = $storage;
}
public function read(string $key): array {
return $this->_storage->read($key);
}
public function write(string $key, array $value): bool {
return ($this->_storage->write($key, $value)) ? true : false;
}
}
所以现在，每次你需要写/读信息时:
$file = new Storage(new File());
$file->write('filename', ['information'] );
echo $file->read('filename');
$session = new Storage(new Session());
$session->write('filename', ['information'] );
echo $session->read('filename');
在这个例子中，你最终在存储构造函数中使用Duck Typing:
function __construct(StorageInterface $storage) ...
def traverse(t):
try:
t.label()
except AttributeError:
print(t, end=" ")
else:
# Now we know that t.node is defined
print('(', t.label(), end=" ")
for child in t:
traverse(child)
print(')', end=" ")
class MyAwesomeClass:
def __init__(self, str):
self.str = str
def __len__(self):
return len(self.str)
class MyNotSoAwesomeClass:
def __init__(self, str):
self.str = str
a = MyAwesomeClass("hey")
print(len(a)) # Prints 3
b = MyNotSoAwesomeClass("hey")
print(len(b)) # Raises a type error, object of type "MyNotSoAwesomeClass" has no len()
