Why Do Standard Iterator Ranges Use a Half-Open Interval [begin, end) Instead of a Closed Interval [begin, end]?

Why are Standard Iterator Ranges [begin, end) Instead of [begin, end]?

The design choice of defining end() as one past the end rather than at the actual end is driven by several key considerations:

Simplified Range Size Calculation:
The open-ended nature of [begin, end) allows for the calculation of the range size as a simple difference between end and begin. This is crucial for efficient iteration and manipulation of ranges.

Natural Handling of Empty Sequences:
Including the lower bound in the range simplifies the handling of empty sequences. Without it, defining a "one-before-the-beginning" sentinel value would be necessary, introducing unnecessary complexity.

Chainable Range-Based Constructions:
The [begin, end) convention facilitates the chaining of multiple nested range-based constructions without incurring off-by-one errors and convoluted code.

Zero-Based Counting:
Starting the count at zero aligns with the natural "beginning" of a range when given a number of elements. This simplifies the representation of ranges as [0, N), removing the need for adjustments or offsets.

In summary, the half-open range convention [begin, end) provides significant advantages in terms of simplicity, efficiency, and readability in dealing with iterators and ranges.

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