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julianaming-conventionsnamingvariable-names

Name a variable with an exclamation in Julia

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

Firstly, it works fine in the JuliaPro Command Prompt

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

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I could not understand how to use an exclamation.

Solution

  • 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.