'_' as an argument in function definition

[abraemer]

See for example this thread:

Usage rules for bare underscores

I’ve seen a few examples where one can use a bare underscore in an expression, e.g., julia> map(_ -> "hello", 1:4) 4-element Array{String,1}: "hello" "hello" "hello" "hello" julia> ["hello" for _ in 1:4] 4-element Array{String,1}: "hello" "hello" "hello" "hello" julia> for _ in 1:4 println("hello") end hello hello hello hello But of course the following doesn’t work: julia> _ = 2 2 julia> _ ERROR: all-underscore identifier used as rvalue However, I haven’t seen a…

The key terminology is that _ cannot be used as an rvalue, which roughly means it cannot appear on the right hand-side of an assignment (or any other expression that is not an explicit assignment).