DBC can be applied to different programming languages, using different syntax and semantics. Some languages have built-in support for DBC, such as Eiffel, Ada, and D. Some languages have external libraries or frameworks that enable DBC, such as Java, C#, and Python. Here are some examples of how DBC can be implemented in different languages:
// Eiffel example
class STACK [G]
feature
count: INTEGER
invariant
count >= 0
item: G
require
not empty
put (x: G)
ensure
count = old count + 1
item = x
remove
require
not empty
ensure
count = old count - 1
end
// Java example using JContractor framework
public class Stack {
private int count;
private Object item;
private StackContract contract = new StackContract();
public Stack() {
contract.Stack(this);
}
public int getCount() {
contract.getCount(this);
return count;
}
public Object getItem() {
contract.getItem(this);
return item;
}
public void put(Object x) {
contract.put(this, x);
count++;
item = x;
contract.putPost(this, x);
}
public void remove() {
contract.remove(this);
count--;
contract.removePost(this);
}
}
public class StackContract extends Contract {
public void Stack(Stack self) {
ensures(self.count == 0);
}
public void getCount(Stack self) {
ensures(result() >= 0);
}
public void getItem(Stack self) {
requires(!self.empty());
}
public void put(Stack self, Object x) {
requires(x != null);
ensures(self.count == old(self.count) + 1);
ensures(self.item == x);
}
public void remove(Stack self) {
requires(!self.empty());
ensures(self.count == old(self.count) - 1);
}
}
# Python example using PyContracts library
from contracts import contract
class Stack:
def __init__(self):
self.count = 0
self.item = None
@contract
def get_count(self) -> 'int,>=0':
return self.count
@contract
def get_item(self) -> 'not_none':
assert not self.empty()
return self.item
@contract
def put(self, x: 'not_none'):
self.count += 1
self.item = x
@contract
def remove(self):
assert not self.empty()
self.count -= 1