Name a variable with an exclamation in Julia

Question

I got confused about using an exclamation to name a variable in this link.

Firstly, it works fine in the JuliaPro Command Prompt

Then, I closed the JuliaPro Command Prompt and opened it again, trying to test different variable namings:

I could not understand how to use an exclamation.

Always put spaces between operators and variables or literals. It is good practice, and makes your code prettier and easier to read. And you avoid parsing pitfalls such as this. — DNF, Feb 11 '18 at 17:40

score 5 · Accepted Answer · answered Feb 11 '18 at 13:15

Add a space after !. Without a space Julia treats != as inequality test.

You can check how Julia parses an expression by using parse function and sending the required expression in a string (and then using dump to see the parsed structure), e.g.:

julia> parse("x! =1")
:(x! = 1)

julia> dump(parse("x! =1"))
Expr
  head: Symbol =
  args: Array{Any}((2,))
    1: Symbol x!
    2: Int64 1
  typ: Any

julia> parse("x!=1")
:(x != 1)

julia> dump(parse("x!=1"))
Expr
  head: Symbol call
  args: Array{Any}((3,))
    1: Symbol !=
    2: Symbol x
    3: Int64 1
  typ: Any

And you can see that the first expression is an assignment and the second is a call to != function.

Name a variable with an exclamation in Julia

1 Answers1