Julia

三元运算符的格式：

a ? b : c

a 是条件表达式，如果条件 a 为真，就执行 b；如果条件 a 为假，就执行 c

二选一

julia> println(1 < 2 ? "1 is smaller than 2" : "1 is bigger than 2")
1 is smaller than 2

julia> println(1 > 2 ? "1 is smaller than 2" : "1 is bigger than 2")
1 is bigger than 2

三选一

julia> f(x, y) = println(x < y ? "x is smaller than y" : x > y ? "x is bigger than y" : "x is equal to y")
f (generic function with 1 method)

julia> f(1, 2)
x is smaller than y

julia> f(2, 1)
x is bigger than y

julia> f(1, 1)
x is equal to y

: 前后的表达式，只有在对应条件表达式为 true 或 false 时才执行

julia> f(x) = (println(x); x)
f (generic function with 2 methods)

julia> 1 < 2 ? f("yes") : f("no")
yes
"yes"

julia> 1 > 2 ? f("yes") : f("no")
no
"no"