Functions for accessing elements of a singleton set in Julia
Overview
Just as a singleton set and its element are distinctly different in set theory, as discussed with singleton set $\left\{ a \right\}$ and its element $a$, in programming, a collection [a] that contains only one element and the unique element a itself are different. While some environments like MATLAB may not distinguish between these in certain situations, Julia does so more strictly, and the function designed for this purpose is only1.
Code
The only function is used in the form of only(x) and directly returns the single element contained in the given collection x. This approach is more intuitive compared to using indexing, like x[1], and it is much safer as it inherently prevents cases where x contains more than one element.
julia> only([1])
1
If x is an empty collection or contains more than one element, an ArgumentError is raised.
julia> only([1,2])
ERROR: ArgumentError: Collection has multiple elements, must contain exactly 1 element
julia> only([])
ERROR: ArgumentError: Collection is empty, must contain exactly 1 element
Environment
- OS: Windows
- julia: v1.10.0