Editing Aggregate pattern (section)

== Computer programming ==

In ''[[Design Patterns]]'', an aggregate is not a [[Software design pattern|design pattern]] but rather refers to an object such as a list, vector, or generator which provides an interface for creating [[iterator]]s. The following example code is in [[Python (programming language)|Python]].
<syntaxhighlight lang="python">
def fibonacci(n: int):
    a, b = 0, 1
    count = 0
    while count < n:
        count += 1
        a, b = b, a + b
        yield a

for x in fibonacci(10):
    print(x)

def fibsum(n: int) -> int:
    total = 0
    for x in fibonacci(n):
        total += x
    return total

def fibsum_alt(n: int) -> int:
    """
    Alternate implementation. demonstration that Python's built-in function sum()
    works with arbitrary iterators.
    """
    return sum(fibonacci(n))

myNumbers = [1, 7, 4, 3, 22]

def average(g) -> float:
    return float(sum(g)) / len(g)  # In Python 3 the cast to float is no longer be necessary
</syntaxhighlight>
Python hides essentially all of the details using the [https://docs.python.org/3/library/stdtypes.html#iterator-types iterator protocol]. Confusingly, ''[[Design Patterns]]'' uses "aggregate" to refer to the blank in the code <code>for x in ___:</code> which is unrelated to the term "aggregation".<ref>[[Design Patterns]], p. 22: "Aggregation implies that one object owns or is responsible for another object. ... Aggregation implies that an aggregate object and its owner have identical lifetimes."</ref> Neither of these terms refer to the statistical aggregation of data such as the act of adding up the Fibonacci sequence or taking the average of a list of numbers.